The Ideal Barrel for a .308 Tactical RifleJanuary 23, 2015 2:39 am
(This article was originally published in Tactical Shooter magazine. The editor comment is from Dave Brennan.) Editor: Recently a TS subscriber wrote to us, looking for some guidance on the barrel contour selection for a .308 chambered tactical rifle. We felt that the inquiry was a bit too broad-based in topic matter and while a scholarly discourse in depth might have been nice… to do the job properly would have taken perhaps a dozen pages… and been a rather dry reading dozen pages at that. Since we live in a “Be practical” type of world, we fired off a “Help!” missive to Dan Lilja, the honcho at Lilja Precision Rifle Barrels (P.O.Box 372, Plains, MT, phone (406) 826-3084), together with a cover letter that mused… “I’m looking for a good, technically-oriented response… but not a rewrite of Gone With The Wind “. The goodfellow, Heaven bless him, must have understood what I was trying to say… because his response was along just the very lines that I was looking for. The editor considers Dan Lilja one of the most knowledgeable of today’s authorities on long range rifle shooting.
To make a recommendation for a .308 caliber barrel to be installed on a Remington 700 action, there are a couple of questions that need to be addressed. The first question is overall rifle weight. For most tactical applications, a rifle in the 10-12 pound range is about right. This rifle weight allows a reasonably heavy barrel for good accuracy, but is not cumbersome when the shooter needs to make a quick entry or exit or a long stalk. And it is hefty enough to hold fairly steady.
Secondly, we’ll look at both bullet selection and barrel contour/length in making a recommendation for a barrel twist rate and profile.
Using the .308 Winchester for a tactical situation, I would like to use a bullet in the 150-180 grain weight range. For longer range shooting, say out to 600 yards, a high ballistic coefficient is desirable to help offset the shooter’s margin of error in estimating wind drift and, if not using a laser range finder, range estimation. With the lower velocities of the 308 Winchester cartridge though, the heavier bullets, with the high ballistic coefficient, tend to be a little too heavy, in my opinion. This extra weight keeps the muzzle velocity down. So a compromise of reasonable muzzle velocities and ballistic coefficient is necessary. The .308 just lacks the horsepower for truly long-range shooting. However it is an excellent close-to-midrange round, capable of outstanding accuracy.
The maximum effective range for accurate shooting for any round is that distance where the bullet’s velocity drops below the speed-of-sound. Depending on the atmospheric conditions, that velocity is near 1120 fps. The 168 grain Sierra Match King is an excellent bullet in the 308 Winchester, and is probably my first choice for the shooting situation we’re discussing in this article. This bullet has a ballistic coeficient of .475 and with a barrel of 26″ or so, a velocity of 2800 fps is reasonable. Using these numbers in an exterior ballistics program, we find that this bullet will go subsonic past 1100 yards. If we were to go to a lighter bullet, like the 150 grain Sierra Match King, with a lower ballistic coefficient of about .440 and a muzzle up to 2900 fps, our supersonic range is no better. Individual rifles and longer barrel lengths will improve on these numbers, but the 308 Winchester is never going to be a 1000 yard powerhouse.
So, if we’re going to settle on the 168 grain Sierra Match King or another bullet of a similar weight and style, then a 12″ twist rate is the best choice. To keep the velocity up, yet keep the rifle handy, I’d opt for a barrel length in the 26-27″ range.
Now the selection for a barrel contour needs to be made. We’ve made a number of barrels for Robar; a company which specializes in rifles of this type. The cover of the January, 2000 issue of Tactical Shooter shows one of Robar’s SR-60 rifles. This special contour that we make for Robar weighs about 5 pounds in a non-fluted condition. It is similar to the contour found on the Remington Police Special rifles and our standard #7 contour. The barrel has enough diameter to remain stiff, and accuracy is excellent. I like this contour for a tactical rifle.
If it is desirable to make the rifle a little heavier, then I would suggest using one of the straight taper barrels, like the NBRSA Heavy Varmint classification or a close variation. We’ve made .30 caliber barrels like this for the Navy SEALS, theirs being a little lighter than the Heavy Varmint taper just mentioned. Finish lengths again would be in the 26-27″ range. If we stepped up to a cartridge like the .300 Winchester, I’d consider going to a 30″ length.
Some readers might wonder why I wouldn’t suggest going even longer than 30″, and there are a couple of reasons why not. One of the primary reasons goes back to our already mentioned requirement for portability. A long barrel just seems to always get in the way, banging against whatever obstacle there might be.
Another good reason is rifle balance. As the barrel gets longer the center of gravity moves forward, tending to make the rifle more and more muzzle-heavy. The rifle can be easily counter-balanced by making the stock heavier, especially in the butt area, but in doing so the overall weight of the rifle becomes higher. Also, too much barrel weight on a lighter-weight repeater action, like our preselected Remington 700, can affect the bedding and create problems that wouldn’t exist with a shorter barrel. It is not unusual to see vertical grouping in a long-barreled, muzzle-heavy rifle. A maximum barrel length of 30″ seems to be a good compromise.
There is one more good reason to stay with a 26-30″ barrel, and that has to do with barrel stiffness. As a barrel gets longer it becomes more limber. The most accurate barrels are the stiffest, all other factors being equal. Increasing the diameter of a barrel has the opposite effect, making a barrel more rigid. But there is a weight penalty in going too large in diameter. If we take a look at the math involved in calculating the rigidity of a rifle barrel it can be modeled after the classic cantilevered beam. For a round beam, like a barrel, its rigidity increases with the 4th power of its diameter but decreases with the 3rd power of its length. The basic formula for calculation of muzzle deflection is:
D = (W*l^3)/3*E*Ix
Where: D is the deflection at the muzzle in inches, W is the force or load applied at the muzzle in pounds, l is the free length of the barrel in inches (not including threads), E is the modulus of elasticity or Young’s modulus for the barrel material, and Ix is the moment of inertia for the barrel.
In plain English this translates into shorter lengths and bigger diameters being stiffer, and as we know, stiffness and accuracy are closely married. Like actual married life there are always trade-offs. Long barrel length means higher velocity but it also means lower stiffness values. Diameters that are bigger mean greater stiffness but the extra weight isn’t always desirable. My wife has told me I can be stiff-necked but that isn’t always desirable either.
Fluting a barrel helps with the compromise though. A fluted barrel retains most of the stiffness gained by increasing diameter, yet reduces the weight gain. And as a side benefit, fluting also increases the cooling rate of a barrel by exposing more surface area to the air.
I ran some numbers through a computer program I developed that calculates barrel weights and stiffness values. In this example I used the NBRSA Heavy Varmint taper. For those not familiar with this profile, it is dimensioned as 1.250″ at the chamber end for 5″. It then begins a straight taper to .900″ at 29″, a taper of .0146″ per inch. In the examples below we’ll start with a 22″ barrel and go on out to 30″. The table will show the weight for each barrel length, the deflection of the muzzle if a one-pound load were applied perpendicular to the bore centerline, and the diameter of the muzzle at the specified length. In all cases the model is for a .308″ caliber barrel.
.308″ caliber NBRSA Heavy Varmint taper barrel stiffness versus length table
|Barrel length in inches||Weight in Pounds & ounces||delfection in inches||muzzle diameter in inches|
So, we can calculate from the above that a 30″ long Heavy Varmint taper barrel will deflect 182% more than a 22″ long barrel will. The difference in length between these two barrels is just 36% and the weight increased just 23%, going from the 22″ to the 30″ barrel. The point is: increasing the length of a barrel quickly decreases its stiffness.
This graph was added in October of 2004 and was provided by Rick. It demonstrates the same information as the table above but in graph form.
Our experience has shown that for a .308 caliber tactical rifle with the overall rifle weight and shooting distances mentioned earlier, a barrel of 24-27″ is optimum in one of the fairly heavy contours we discussed. Closer ranges or other considerations might dictate a shorter barrel. The vast majority of the barrels we make for the professionals, who have made their own decisions on barrel length and profile, also fall into these same parameters.
(As of February of 2004 we have added a new straight taper to our list of standards that we refer to as the Tactical. It was developed by one of our military customers. It is a 1.200″ diameter cylinder for 4″ and then a straight taper to .800″ at 26″. The weight at this length is 5.55 pounds in .30 caliber.)
308 Winchester / 7.62x51mm NATO: Barrel Length versus Velocity (28″ to 16.5″)
Released by Winchester in 1952 (and adopted by NATO in 1954 as the 7.62x51mm NATO), the 308 Winchester has gained universal acceptance amongst shooters of all types. Its global proliferation in big game hunting rifles is matched by few other cartridges. Nearly every target shooter had his teeth cut on a 308 Winchester. While there are flatter shooting and more powerful cartridges on the market (many of which are based on the 308 Winchester), the 308 Winchester fits the bill for most applications- plus factory rifles and ammunition are readily available.
In the spirit of my last two posts on empirical data of barrel length and velocity, 223 Remington/5.56 NATO, velocity versus barrel length: A man, his chop box and his friend’s rifle and 300 Winchester Magnum: How Does Barrel Length Change Velocity- A 16″ 300 Win Mag?, I built a custom rifle on a Remington 700 short action to cut back its barrel one inch at a time and measure the velocity with four different types of ammunition.
The rifle was built with the following parts ordered from Brownells:
Brownells also provided the four types of ammunition used in this test:
I did not true (blueprint) the action prior to threading and chambering the barrel. I also took the time to groove the barrel in one inch increments from 16.5″ to 28″ as a cutting guide. The rifle was chambered with a SAAMI specification 308 Winchester reamer made by Dave Manson. Headspace was measured at 1.633+ (.003″ over minimum).
What was the test protocol?
Ballistic data was gathered using a Magnetospeed barrel mounted ballistic chronograph. At each barrel length, the rifle was fired from a front rest with rear bags, with five rounds of each type of ammunition. Average velocity and standard deviation was logged for each round. Note: I also fired a 30 shots of the IMI Samson 7.62mm 150 grain FMJ with the 28″ and 16.5″ lengths- I’ll discuss why later. Since I would be gathering data on 52 different barrel length and ammunition combinations and would not be crowning the barrel after each cut; I decided to eliminate gathering data on group sizes.
Once data was gathered for each cartridge at a given barrel length, the rifle was cleared and the bolt was removed. The barrel was cut off using a cold saw. The test protocol was repeated for the next length.
Temperature was 47F.
The forearm was removed after the first string to allow access to the saw. Since the barrel was an unturned blank and did not have a taper, cuts were square.
All shooting was done from a bench, with a Sinclair rest and rear bag.
|308 Winchester Barrel length in inches versus Muzzle velocity in feet-per-second (ft/sec)|
|Barrel length||Winchester 147 FMJ||IMI Samson 7.62 150 FMJ||Federal 168 Gold Medal||Winchester 180 PP|
|AVG velocity loss fps/inch||24.6||22.8||20.9||22.5|
The data presented as a line chart
Cartridge specific information
Barrel length in inches versus Muzzle velocity for Winchester 147 Grain FMJ
|Barrel length inches||Winchester 147 FMJ||SD||Change ft/sec velocity||Change ft/sec velocity from 28″|
Barrel length in inches versus Muzzle velocity for IMI Samson 7.62mm 150 Grain FMJ
|Barrel length inches||Samson 7.62 147 FMJ||SD||Change ft/sec velocity||Change ft/sec velocity from 28″|
Barrel length in inches versus Muzzle velocity for Federal Gold Medal 168 Grain Match BTHP
|Barrel length inches||Federal 168 Gold Medal||SD||Change ft/sec velocity||Change ft/sec velocity from 28″|
Barrel length in inches versus Muzzle velocity for Winchester 180 Grain Power-Point Ammunition
|Barrel length inches||Winchester 180 PP||SD||Change ft/sec velocity||Change ft/sec velocity from 28″|
Cutting the barrel from 28″ to 16.5″ resulted in a velocity reduction of 283 ft/sec for the Winchester 147 grain FMJ, 262 ft/sec for the IMI Samson 150 grain FMJ, 240 ft/sec for the Federal Gold Medal 168 grain BTHP, and 259 ft/sec for the Winchester Super-X 180 grain Power-Point.
Average velocity loss from 28″ to 16.5″, was 24.6 ft/sec per inch for the Winchester 147 grain FMJ, 22.8 ft/sec per inch for the IMI Samson 150 grain FMJ, 20.9 ft/sec for the Federal Gold Medal 168 grain BTHP per inch, and 22.5 ft/sec per inch for the Winchester Super-X 180 grain Power-Point.
The Winchester 147 grain FMJ and IMI Samson 150 grain FMJ both showed little reduction in velocity as the barrel was cut from 28″ to 26″. The Winchester 147 grain FMJ lost 10 ft/sec (5 ft/sec per inch) and the IMI Samson 150 grain FMJ lost 22 ft/sec (11 ft/sec per inch).
2/1/16- Short barrel information can be found at:
308 Winchester/ 7.62x51mm NATO Short barrel length and velocity- A six inch 308 bolt gun?
1/24/15- Complete data sets for each cartridge can be found in the following posts:
308 Winchester Barrel Length and Velocity: Winchester 147 grain FMJ
7.62x51mm NATO (308 Win) Barrel Length and Velocity: IMI Samson 150 grain FMJ
308 Winchester Barrel Length and Velocity: Federal 168 grain Gold Medal BTHP
308 Winchester Barrel Length and Velocity: Winchester Super X 180 grain Power-Point
How did barrel length change exterior ballistics?
We ran the 147, 150 and 168 grain loads for 28″, 24″, 20″ and 16.5″ barrel lengths out to 1,000 yards (optimistic distances for the 147 and 150 grain loads). Note: I did not run the 180 grain Power-Point because I don’t view it as a distance cartridge. These graphs assume a 1.75″ height of the optic over the bore and weather conditions of 59F.
Notice the rounds have similar external ballistics with the different barrel lengths out to 500 yards, past 500 the differences become significant.
How did barrel length affect Maximum Point Blank Range (MPBR)?
Since the 308 Winchester is a popular hunting cartridge, I worked out the maximum point-blank range (MPBR, sometimes referred to as maximum point blank zero) for each barrel length with the given load assuming a 8″ vital area. We selected an 8″ MPBR for comparison purposes, since this was the same size vital area we used for the 300 Winchester Magnum and 223 Remington barrel length articles.
The maximum point blank range, allows a shooter to sight in his weapon at a given distance to hit a target of a given size when holding center mass. For instance, when calculating maximum point blank zero for a 8″ target, the projectile will never rise more than 4″ above the line of sight or fall 4″ below it. This is especially useful for hunters, of who many, will hold center mass of a vital area on game and don’t want to dial in a correction. My calculations assume a 1.75″ sight over bore height.
|308 Winchester Maximum Point Blank Range (MPBR) in yards for 8” Target|
|Barrel length||Win 147 FMJ||IMI Samson 150 FMJ||Federal GM 168 BTHP||Win 180 Power-Point|
|Change in MPBR||-29||-27||-25||-27|
Note the change in MPBR averages 27 yards with an 11.5 inch change in barrel length.
What are possible sources of error in your experiment?
Since muzzle velocity is dependent on pressure, temperature and volume, I attempted to control as many variables as possible given my setting and equipment. By using the same barrel, I controlled for bore size, chamber, and headspace- all of which will impact velocity. Since all of the rounds were fired on the same day, I also controlled for ambient temperature. I did not control for barrel temperature. The barrel did heat up during firing. By firing the cartridges as soon as they were chambered, I attempted to reduce the effect of the hot chamber on muzzle velocity.
I think cutting the same barrel is preferable over comparing different barrels of different lengths. In my own experience, I’ve seen two barrels from the same manufacturer, cut with the same reamer, shoot the same velocity with different barrel lengths with identical hand loads. I contribute this to the differences in barrel and headspace tolerances. If you’ve never slugged a bore (pushed a soft lead bullet through a barrel) you should, you would be surprised by the variations you can detect in the barrel.
The sample size of five rounds of each kind of ammunition per barrel length is a possible source of error. However, testing indicates it may not be as much as initially thought. I fired 30 rounds of IMI Samson 150 grain FMJ at 28″ and 16.5″ and recorded the results. Comparing the data from the 30 shot strings (28″ 2824 and 16.5″ 2555) to the 5 shot strings (28″ 2823 and 16.5″ 2561) I found a loss of 269 ft/sec (23.4 ft/sec per inch) as the barrel was cut. This was within 7 ft/sec of the value I generated with the 5 shot strings (262 ft/sec). Velocity loss per inch of barrel was .6 ft/sec away (22.8 ft/sec) from the value calculated with 5 shot strings.
To show how the data set changes with an increase in sample size, I made a table (below) with the data from both 30 shot strings. The “shot” column represents the shot number in the respective string. “28” barrel ft/sec” and “16.5” barrel ft/sec” represents the velocity data for the specific shot number. “AVG 28″ ft/sec” and “AVG 16.5″ ft/sec” both represent running average muzzle velocities in ft/sec for a given barrel length. “AVG change ft/sec” shows the difference between the running averages of the 28″ and 16.5″ barrels. “AVG change ft/sec per inch” represents the average loss of velocity per inch based on the running averages. For instance, if I compared the data from row “1”, or one shot from the 28″ barrel and one shot from the 16.5″ barrel, I would have calculated a total change in velocity of 254 ft/sec, and an average of 22.1 ft/sec per inch. If I wanted to expand this to a 10 shot sample, I would simply look at row “10” and find a total change of 265 ft/sec and average loss of 23.0 ft/sec per inch of barrel. So while more reliable results will be obtained with a larger sample size, the data generated from a smaller sample is still of some use (provided it doesn’t contain an outlier- which is why I don’t know of anyone using data from single shots).
308 Winchester/ 7.62x51mm NATO Comparison of velocity data
|Shot||28″ barrel ft/sec||AVG 28″ barrel ft/sec||16.5″ barrel ft/sec||AVG 16.5″ barrel ft/sec||AVG change ft/sec||AVG change ft/sec per inch|
Why did you pick these cartridges?
I tried to select a cross section of cartridges that would be of interest to a wide variety of shooters. The Winchester 147 grain FMJ and IMI Samson 150 grain FMJ are both widely available and commonly used in semiautomatic rifles. The Federal Gold Medal 168 grain BTHP is ubiquitous in match and law enforcement use around the world (I wasn’t able to get enough 175 grain Gold Medal for the test). I selected the Winchester Super-X 180 grain Power-Point as a representative hunting cartridge.
How did your findings compare to a reloading manual?
They were fairly close. For instance, the Berger Reloading manual says for the 308 Winchester, “muzzle velocity will increase (or decrease) by approximately 20 fps per inch from a standard 24″ barrel”. My data showed an average change of 27 ft/sec per inch of barrel.
Did you shoot any groups?
No, I did not. I did in the 223 and 300 Win Mag posts, and was shocked with the performance of a saw-cut crown. Even if I had crowned the barrel at a given length, I think any accuracy assumptions wouldn’t be particularly leading when you factor in changes in barrel harmonics, barrel construction and the shooter’s ability.
Why didn’t you crown the barrel?
Time. My lathe is a two hour round trip to the range. Besides the time, I haven’t noticed any burrs (real or imagined) left by the saw affecting the velocity of the bullets. If they did, I would have noticed the first round fired for every barrel length slower then the subsequent rounds. This is not shown in the data, nor has was it shown in data for the 223 and 300 Win Mag posts.
Why didn’t you discuss the difference between 308 Winchester and 7.62×51 mm NATO?
It is outside the scope of this post. There are plenty of good sources of information on this topic. The IMI Samson 150 grain FMJ is a 7.62x51mm NATO spec cartridge.
What’s your thought on short barrel 308 Winchesters?
I like them- in some ways you don’t lose a lot. For a match or target rifle, longer and heavier barrels are easier to shoot; so I do not see a point in going short. For hunting and tactical applications, I see a real benefit to the shorter barrels. If you take a look at the series posts (below) on my 16.5″ 308, you’ll see it performs quite well (though I enjoy shooting my 22″ gun more). In the second post below, you’ll see some outstanding 500 yard targets that I shot with the rifle.
Super Short Precision Rifles: Is there such thing as a 16.5″ .308 Tactical Bolt Action Rifle?
Short Rifle, Long Range: Testing our 16.5″ 308 Remington 700 out to 635 yards,
16.5 Inch 308 Winchester Precision Rifle: Summary of a Short Rifle
My 16.5″ 308 Winchester (above) is a fun little rifle.
My 22″ 308 Winchester (above) is my favorite rifle to shoot.
How did you measure your headspace within .001″? I have a go and a no-go gauge, that’s it.
I use a Forster Match Rife Headspace Gauge Kit. It includes gauges in .001″ increments.
Are you aware of any similar studies?
I’ve referenced a few other 223 Remington studies in my prior posts. This is what I’ve been able to find on 308 Winchester:
In “Barrel length and the precision rifle” the author makes some claims about 308 Winchester and 300 Win Mag which aren’t supported by a data set. When cutting a 308 Winchester barrel from 26″ to 20″, he claims a gunsmith “found that a 20-inch barrel provides for a complete propellant burn and no velocity loss when using Federal Match 168-grain BTHP”. I think he may be misquoting his source. Maybe he meant negligible?
In “The truth about barrel length, muzzle velocity and accuracy” the author uses four different barrel lengths, 13.5″, 16″, 18″ and 26.5″, and eight different cartridges. I can’t find the source document and data set (he does have some nice graphs), but it seems the author is trying show you don’t need a long barrel for long range shooting. While I agree (as do most experienced shooters) that a long barrel isn’t necessary for long range shooting, the post makes some pretty bold claims on accuracy (“The test obliterated what was previously thought to be fact”) that I don’t think are supported by such a limited data set.
“Effect of Barrel Length on the Muzzle Velocity and Report from a Mosin-Nagant 7.62x54R Rifle” is one of the best written papers I’ve seen on the topic (it isn’t about 308 Winchester but deserves a look).
How much did muzzle blast change?
The rifle with a shorter barrel was louder. This was noticeable from 19 inches and below. Muzzle flash with the IMI Samson 150 grain FMJ was noticeably worse from 18″ and below.
So you built a custom rifle just to cut it apart?
Yes, I guess I did. I got the longest blank I could and went from there. Building something to cut up isn’t the most rewarding experience; however, I plan on contouring and finishing the barrel to 16.25″ (that’s why I stopped at 16.5″).
UPDATE 12/30/14: I tapered the barrel and installed a brake. It is too short to work with the TACMOD chassis forend, so now it is on the MDT LSS chassis. The bottom picture is the first group I shot with the rifle, 5-shots, .785″ including cold bore. Here are some pics:
Why are you destroying a rifle? Wasting bullets?
I get this every so often. I am cutting up a barrel. The rifle is fine. I will actually contour what is left and use it on a custom build. I think data sets are great. No guessing, no models, no arbitrary numbers. I think the value of this data is worth the time, effort and expense. I post it here, for free, so other shooters can learn from it.
I see you upgraded from a hacksaw?
Yes, I did for the 223 post. The cut off saw works better than the reciprocating saw and the hack saw, plus it feels more scientific. I may wear a lab coat to kick things up another notch next time.
Do you like the TACMOD chassis system?
Yes, I am very impressed. Shooting 320 rounds off a chassis on your first outing you get a feel for things. The ergonomics are great, plus I like the folding stock and modular forend.
Where can I find your 223 Remington and 300 Winchester Magnum barrel length posts?
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More great content!
I woke up early that morning. It was only a few days after a historic blizzard passed through my state. Stir crazy, I couldn’t wait to get outside. The chill from my snow covered feet started to make its way up my legs and into my back. I shook vigorously from head to toe. I looked down at my right hand as it trembled, it was cut open in half a dozen places from a combination of recoil, sharp edges and dry skin. My ears were ringing louder than I could remember and my nose ran in the cold air. The gun and support equipment weren’t in much better shape. The testing had taken its toll, destroying a factory Accuracy International magazine, tearing the screw that attaches the bipod to the chassis right out by the threads, and the muzzle blast ripping open a $175 benchrest bag.
You’d think I was disappointed, however, there was a smile on my face. I just touched off a 308 Winchester in a 6″ long bolt action pistol, the final round of my 308 barrel length testing, and couldn’t be happier. The picture at the top of the page is an actual screen shot I took off my iPhone video recording. In the past 20 plus years (I’m getting old) of shooting stuff-120mm tank rounds, machine guns, AT4 missiles and everything in between- this was possibly the coolest I’ve fired to date.
Over the past few years, Rifleshooter.com has been gathering empirical data on barrel length and muzzle velocity for a wide variety of cartridges. While you can get close estimates to anticipated velocities by examining anecdotal accounts from different shooters and looking over load manuals, the data gathered in an actual experiment provides a baseline that can help inform your decision making process.
In 308 Winchester / 7.62x51mm NATO: Barrel Length versus Velocity (28″ to 16.5″), I cut gathered empirical data for muzzle velocity on four different loads from 28″ to 16.5″. Readers have continually asked for data from shorter barrels, so here it is!
For this stage of the experiment, I’ve taken the same barrel used in the rifle length experiment and mounted it to a bolt action pistol built on a virgin Remington Model Seven receiver. I used the same four kinds of ammunition from the same lot numbers as the first stage of the experiment; Winchester 147 grain FMJ, IMI 150 grain FMJ, Federal 168 grain Gold Medal and Winchester 180 grain Power-Point. Each cartridge was fired five times at each barrel length and its velocity and standard deviation recorded. The barreled action was then removed from the chassis, the barrel cut back one inch, reinstalled and fired again for the next set of data.
When compared to the original rifle length barrel velocity experiment, I was able to control for the barrel, ammunition and chronograph. Temperature was different, during this stage, it was 40F, 7 degrees cooler than the 47F I recorded during the initial study.
Initial testing was done on Remington 700 action in a rifle. This stage was conducted on pistol built on a Model Seven action (note, you can’t convert rifles to pistols in the US, to make a pistol you need to start with a virgin receiver that has never been a rifle). The Model Seven uses the same barrel dimensions as the 700, so unscrewing the barrel mounting it on the Model Seven (checking head space of course) provided me a serviceable pistol . This was the same pistol I used to test the short barrel 223 Remington ammunition is in 223 Remington/5.56mm NATO Barrel length versus Velocity- Short Barrels- 6 to 14 inches. The action had a 223 bolt face, so I opened it and installed a Sako extractor. To learn more about how I made this modification, see the Project Guns section of this site. The headspace on this pistol measured 1.630″ (SAAMI minimum), this was .003″ less that when the barrel was installed on the rifle (1.633″).
Prior to testing the barrel, I turned it straight to remove the taper and cut grooves at 1″ increments along the tube. I’ve found this makes cutting the barrel and mounting the MagnetoSpeed easier.
Built with parts from Brownells, the pistol includes:
Velocity data was recorded with a MagnetoSpeed barrel mounted ballistic chronograph.
The contents of Rifleshooter.com are produced for informational purposes only and should be performed by competent gunsmiths only. Rifleshooter.com and its authors, do not assume any responsibility, directly or indirectly for the safety of the readers attempting to follow any instructions or perform any of the tasks shown, or the use or misuse of any information contained herein, on this website.
A summary of the data for all four cartridges is provided below
Due to ammunition constraints, data for the Winchester 147 grain FMJ and Federal 168 grain Gold Medal was gathered until 8″ and Winchester 180 grain Power-Point 9″. IMI 150 grain FMJ 7.62x51m NATO data was gathered down to a 6″ barrel length.
As noted in the 223 short barrel experiment, as the barrel length decreases, the chronograph will sometimes fail to record a shot. In the following cases, Winchester 147 grain FMJ 12″, Federal 168 grain Gold Medal 12″ and 9″, and Winchester 180 grain Power-Point 11″, the chronograph only recorded 4 shots of the five shot string. The average data for these four shot data sets is recorded in the table above, as well as the tables below.
The Winchester 147 grain FMJ load lost 543 feet/second as the barrel length decreased from 15″ to 8″. This was an average decrease of 77.6 feet/second per inch of barrel length. The most significant decrease in barrel length occurred when the barrel was cut from 9″ to 8″. This resulted in a velocity loss of 118 feet/second.
The IMI 150 grain FMJ 7.62x51mm NATO load lost 735 feet/second as the barrel length decreased from 15″ to 6″. This was an average decrease of 81.7 feet/second per inch of barrel length. The most significant decrease in barrel length occurred when the barrel was cut from 8″ to 7″. This resulted in a velocity loss of 137 feet/second.
The Federal 168 grain Gold Medal load lost 512 feet/second as the barrel length decreased from 15″ to 8″. This was an average decrease of 73.1 feet/second per inch of barrel length. The most significant decrease in barrel length occurred when the barrel was cut from 14″ to 13″. This resulted in a velocity loss of 106 feet/second.
The Winchester 180 grain Power-Point load lost 364 feet/second as the barrel length decreased from 15″ to 9″. This was an average decrease of 60.7 feet/second per inch of barrel length. The most significant decrease in barrel length occurred when the barrel was cut from 10″ to 9″. This resulted in a velocity loss of 94 feet/second.
What did you learn?
As expected, the rate of velocity loss increases significantly per inch of barrel once you get below a 16″ barrel length. Compare the above rates of loss to those found in 308 Winchester / 7.62x51mm NATO: Barrel Length versus Velocity (28″ to 16.5″), where the Winchester 147 grain FMJ averaged 24.6 feet/second per inch of barrel, IMI 150 grain FMJ averaged 22.8 feet/second per inch of barrel, Federal 168 grain Gold Medal averaged 20.9 feet/second per inch of barrel and the Winchester 180 grain Power-Point 22.5 feet/second per inch of barrel.
Doyou see any use for a 10″ 308 Winchester?
No, personally, it seems like a silly idea to me. Based on my limited experience with the 330 BLK and 7.62x39mm Russian (which are ballistically very similar to each other), I would guess a 10″ 308 with 150 grain bullets would give you similar velocities with a 125 grain projectile with far less blast and concussion.
What are possible sources of error in your experiment?
The small sample size is always an issue. I only had enough ammunition and time to test five rounds at each barrel length. Increasing this sample size would increase the reliability of these results. For more on sample size, see the discussion here.
Did it really hurt to shoot a short 308 pistol?
Yes, it did. I’ve shot a lot of different firearms in my life and this wasn’t pleasant. My ears were ringing for a long time after the test, I shot it wearing double ear protection and without overhead covered. It was LOUD.
The brand new, factory AI AICS magazine also flew apart as few times. I actually had this happen on two different mags. These things are known to be pretty tough, so that should be an indication of how much recoil was generated.
The muzzle blast from the short barrel eroded away some of the chassis!
Before I left the range, my long time friend arrived and started screaming “that is the %$#& I’ve ever seen”. I offered to let him shoot it. He declined. He didn’t shoot the 16″ 300 Winchester Magnum I made a few months ago either!
Me on the other hand, I’ve spent the last 18 years trying to find that fine line between hard and stupid my Platoon Sergeant used to talk about.
What do you think of the MDT LSS chassis?
I like it a lot. Super easy to install and remove the action from the stock. Good ergonomics, and a great value for the money. Please see Modular Driven Technologies (MDT) LSS Chassis Review. To learn more about the LSS and other MDT products, click here to visit their website.
Is the file picture at the top of the page real, or photoshopped?
100% real. I used my iPhone to record a couple shots being fired in slow motion. Out of the 4 recording I made, only two frames contained muzzle flash. This was the best one. In the next frame you can see the gun recoiling (below).
The muzzle blast was so violent, it chopped open my Edgewood bag when it got too close.
How did the Sako extractor work?
Flawlessly. I had 100% extraction during the course of this experiment.
How did the Timney 510 trigger work?
Very well. I’ve been beating on the 510 and 517 for a while. No complaints, no problems. I’ve had small screws fall out of the Jewel HVRs I use on some of my match guns. These seem much more durable over the long run.
Do you trust the results from the MagnetoSpeed?
Yes, I do. I leave my Oelher 35P in the truck now. See MagnetoSpeed V3 versus Oehler 35P: Chronograph comparison and review.
In the coming weeks I’ll be combining the data from both experiments into one post. When that happens I’ll post a link there. Until then, stay safe.
More great content!
.308 Win Barrel Cut-Down Test: Velocity vs. Barrel Length
With barrels, one wonders “Can a little more length provide a meaningful velocity gain?” To answer that question, Rifleshooter.com performed an interesting test, cutting a .308 Win barrel from 28″ all the way down to 16.5″. The cuts were made in one-inch intervals with a rotary saw. At each cut length, velocity was measured with a Magnetospeed chronograph. To make the test even more interesting, four different types of .308 Win factory ammunition were chronographed at each barrel length.
Test Barrel Lost 22.7 FPS Per Inch (.308 Win Chambering)
How much velocity do you think was lost, on average, for each 1″ reduction in barrel length? The answer may surprise you. With a barrel reduction from 28″ to 16.5″, the average speed loss of the four types of .308 ammo was 261 fps total. That works out to an average loss of 22.7 fps per inch. This chart shows velocity changes for all four ammo varieties:
Summary of Findings: The average velocity loss per inch, for all four ammo types combined, was 22.7 FPS. By ammo type, the average loss per inch was: 24.6 (Win 147 FMJ), 22.8 (IMI 150 FMJ), 20.9 (Fed GMM 168gr), and 22.5 (Win 180PP).
Interestingly, these numbers jive pretty well with estimates found in reloading manuals. The testers observed: “The Berger Reloading manual says for the 308 Winchester, ‘muzzle velocity will increase (or decrease) by approximately 20 fps per inch from a standard 24â³ barrel’.”
How the Test Was Done
The testers described their procedure as follows: “Ballistic data was gathered using a Magnetospeed barrel mounted ballistic chronograph. At each barrel length, the rifle was fired from a front rest with rear bags, with five rounds of each type of ammunition. Average velocity and standard deviation were logged for each round. Since we would be gathering data on 52 different barrel length and ammunition combinations and would not be crowning the barrel after each cut, we decided to eliminate gathering data on group sizes. Once data was gathered for each cartridge at a given barrel length, the rifle was cleared and the bolt was removed. The barrel was cut off using a cold saw. The test protocol was repeated for the next length. Temperature was 47° F.”
CLICK HERE to Read the Rifleshooter.com Test. This includes detailed charts with inch-by-inch velocity numbers, multiple line charts, and complete data sets for each type of ammo. Rifleshooter.com also offers ballistics graphs showing trajectories with different barrel lengths. All in all, this was a very thorough test by the folks at RifleShooter.com.
Much Different Results with 6mmBR and a Longer Barrel
The results from Rifleshooter.com’s .308 barrel cut-down test are quite different than the results we recorded some years ago with a barrel chambered for the 6mmBR cartridge. When we cut our 6mmBR barrel down from 33″ to 28″, we only lost about 8 FPS per inch. Obviously this is a different cartridge type, but also our 6mmBR barrel end length was 5″ longer than Rifleshooter.com’s .308 Win start length. Velocity loss can be more extreme with shorter barrel lengths (and bigger cartridges). Powder burn rates can also make a difference.
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Tags: .308 Win, 7.62x51 cut-down test, Barrel, Rifleshooter.com, Saw, Velocity
Permalink- Articles, GunsmithingSours: http://bulletin.accurateshooter.com/2015/06/308-win-barrel-cut-down-test-velocity-vs-barrel-length/
Inch 308 by the ballistics
308 Ballistics Chart & Coefficient
Article Posted: July 10, 2012
The following is a 1000 yard .308 ballistic chart that was created using our free online ballistic calculator and details all aspects of the bullets trajectory from the millisecond it leaves the barrel until the time it reaches the 1,000 yd mark. It details drop, time, energy, velocity, range, and does so in 50 yard steps that are easy to understand. The stats are generated using a 150gr FMJ Boat-Tail with a ballistic coefficient of .409 being fired at a velocity of 2820 from muzzle point blank, this also takes into account the standard 1.5" scope height, and a gun that has been sighted in at 100 yards. If your .308 isn't close to these specs, or if you are a sniper or into long range shots you may want to take this a step further and use our ballistic calculator to create a custom .308 ballistic chart to take into account variances. You can then also add atmospheric conditions and angles.
Create Your Free Custom Ballistic Report
A A .308 Winchester (7.62mm NATO), American Eagle (Federal) Full Metal Jacket Boat-Tail, 150gr
So what does the charting of the .308 Winchester's external ballistics tell us exactly? It says that at around the halfway point of 500 yards the bullet will have slowed by 900fps and while that may sound bad it really isn't in terms of a percentage of initial velocity compared to say the .223 Remington (would be 1481fps from initial 3214fps) or the 7.62x39mm (would be 1066fps from initial 2349fps). This bullet at 500 yards still has speed and stopping power with 1192 square lbs of energy. In fact the .308 Winchester 165gr bullet is traveling faster at 1000 yards than the .223 or 7.62x39mm at just 500 yds.
Create Your Free Custom Ballistic Report
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ATTENTION: Effective Sept 1, 2020, the BBTI Project is in "Archive Status." No further tests will be conducted, but we will maintain this site and data for the use of the firearms community. Thank you.
Welcome to Ballistics By The Inch, or 'BBTI' as people have taken to calling it.
Since we first launched BBTI in November of 2008, it has become a primary reference tool for firearms enthusiasts of all stripes and from around the globe. Our initial research data covered the relationship between barrel length and velocity for some 13 common handgun calibers/cartridges. In response to the phenomenal popularity of the site, we've continued to do testing, and have expanded the data to include an additional 8 handgun calibers/cartridges (and a repeat of the .380 Auto tests with additional ammunition) as well as the .223 rifle cartridge. We've also conducted a major study of the 'cylinder gap effect' on a revolver, involving more than 6,000 rounds fired, as well as a comparison of the performance differences between polygonal and traditionally rifled barrels. As always, all of our data is freely available, though we happily accept donations (see button below left)and would greatly appreciate your tangible support to help us continue the project.
Up above you'll find links to four main pages:
- Calibers/cartridges will take you to a list of all 22 different data sets. You can just browse the charts, click on a given ammunition type listed in the header of each chart for a graph of how that particular ammunition performed, or download the raw data for your own use.
- Cylinder gap will take you to the results of that study, which used an Uberti Single Action Army clone in .38/.357 mag to examine velocity differences between three different cylinder gaps (0.006", 0.001", and 'flush').
- polygonal rifling will take you to the newest part of our site, documenting performance comparisons between polygonal and traditionally rifled barrels in 9mm.
- Real world guns will take you to a comprehensive list of all the firearms we used as 'benchmark' comparisons for results obtained from our T/C Encore test platform. You'll also see "review" listed after a number of the guns, which will take you to a review of that particular gun (or a closely related model) over at Guns.com written by Jim Downey of the BBTI team (who is also a writer for Guns.com).
Along the left side there you'll find some more basic information about BBTI.
As we've noted previously, we have no illusions that our data is comprehensive. It is meant to be indicative - giving an indication to the general relationships between barrel length and velocity, or the effect of a cylinder gap, or how polygonal and traditionally rifled barrels perform. It would be impossible (for us, at least) to test all the different ammunition types available, or all the different firearms - particularly so when manufacturers of ammunition and firearms are constantly tweaking and improving their products. So use the data here to get an idea of what to expect, and perhaps as a jumping-off point for your own research.
Thanks for coming by.
Other ResourcesBBTI is not the end-all of ballistics testing, just one more component available for the common good. In addition to extensive discussion about ballistics to be found at many gun forums, here are some other great resources pertaining to ballistics testing you should check out. (And if you would like to recommend a site to list here, please send an email.)
- BrassFetcher: excellent resource, with an emphasis on bullet performance in ballistic gelatin
- The Box O' Truth: testing ammo penetration through various barriers
- Terminal Ballistics Research: Specializes in the research of cartridge & projectile performance, using hard data gathered from 20 years of hunting game.
We'd like to personally and specifically thank Pat Childs at Fin & Feather in Iowa City, as he not only helped get most of our ammunition and other supplies, he was the brilliant gunsmith who worked with us to make this insane project much more practical. Without his help all of this would have been much more difficult and perhaps impossible. Anyone who uses our data owes him a debt of gratitude.
And thanks to our spouses, who were not just tolerant but enthusiastically supportive of this rather nutty project.
This project, and all of its results, is only our fault. We (well, Jim K, mostly) paid for everything ourselves, and we did not receive any kind of sponsorship or remuneration from anyone. We did all the work. We used products we were either familiar with, or because they were what was available, and mentioning them by name does not constitute an endorsement of any kind. Furthermore, the data is provided purely for entertainment purposes - to better facilitate arguments over what ammo or caliber or gun is "best." How you use the data is entirely up to you. And if you think you could do better, feel free to spend the money and do the work and publish your own results. Or not. Your choice.
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And then I took out my patch strap, and, being in my underwear, fastened it at the level of the hips. Lie on your stomach. Ilyusha. In the meantime, I'll prepare the lubricant.