Rifleshooter.com’s Barrel Length And Velocity Tests

308-barrel-length-file-photo2

Following up on their test of 5.56mm and .300 Winchester Magnum ammunition velocities through different barrel lengths, Rifleshooter.com has posted a velocity vs. barrel length examination of .308 Winchester. One of the most well-balanced and versatile .30 caliber rounds in history, the .308 Winchester proved surprisingly well suited to almost all barrel lengths tested, with Winchester 147gr ammunition ranging from almost 3,000 ft/s from a 28″ barrel to just under 2,700 ft/s from a 16.5″ barrel:

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.

Results

308 Winchester Barrel length in inches versus Muzzle velocity in feet-per-second (ft/sec)Rifleshooter.com
Barrel length Winchester 147 FMJ IMI Samson 7.62 150 FMJ Federal 168 Gold Medal Winchester 180 PP
28 2965 2823 2706 2632
27 2962 2800 2697 2607
26 2955 2801 2673 2597
25 2917 2769 2659 2585
24 2909 2766 2635 2553
23 2877 2744 2618 2553
22 2837 2718 2597 2527
21 2807 2683 2580 2507
20 2804 2679 2565 2478
19 2757 2634 2532 2441
18 2739 2595 2523 2411
17 2707 2577 2481 2401
16.5 2682 2561 2466 2373
AVG velocity loss fps/inch 24.6 22.8 20.9 22.5

The data presented as a line chart

 

308 optimum barrel length chart

 

These sorts of studies can really help readers understand their subjects better. Especially when methodology is recorded meticulously like this, not only are the data helpful for determining ballistics from a rifle of known barrel length, but also what barrel length is right for a certain purpose.

And just maybe, Rifleshooter’s 16.5″ barrel length results with 147gr ammunition have me taking a second look at that 16.25″ barreled DSA SA 58 at my local gun shop…

Be sure to follow the link and read the whole thing.



Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He can be reached via email at nathaniel.f@staff.thefirearmblog.com.


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  • iksnilol

    Interesting, always nice to have more data. Though I am curious, how much of an effect does velocity reduction have at long distances (1 km)? As in, how many clicks of difference would there be if I was shooting at 1000 meters (not yards) with a rifle with a 50 cm (20 inch) or a rifle with a 60 cm (24 inch) barrel? Presuming standard 168 grain (or 175 grain) match ammo is used.

    Looking at the numbers the difference between 50 and 60 cm barrel is about 21 m/s (70 feet) for the heavier bullets and about 30 m/s (100 feet) for the lighter bullets. That doesn’t seem like a big difference but how big difference is it at 1 km? Or 1.2 km?

    • Appalachian American

      The article shows graphs with velocity and drop out to 1250 yards.

      • iksnilol

        Oh, I didn’t read the article. Now I feel kinda stupid. Thanks for the help.

  • Dracon1201

    Those tags, though.

  • vss

    ballistics by the inch has done this for multiple calibers years ago

    • Sadler

      They’ve almost entirely done handgun cartridges, though. They haven’t done .300WM or .308, so this is pretty interesting, but it’s not like this information isn’t already out there.

      • Rifleshooter

        I am the author of the post he linked to. Show me the data sets you are talking about- there aren’t any. This is empirical data, not a model and not a guess. I’ve linked to all other studies of a similar nature over the course of my 3 posts.

    • Bill

      Not for rifle cartridges. He’s a cool dude, I link to him

  • wildbillb

    ouch. i don’t think the data is worth the cost of a barrel… interesting, but not THAT interesting.

    • sauerquint

      For SCIENCE!

      • Bill

        I still have the barrel and shoot it on another gun. Read the post my LSS and HS3 reviews.

  • temper

    Forgot 175 SMK, the most popular precision round for .308.

    • Bill

      I shoot what they send me. They sent me 168. Your loss will be similar with the 175. I would argue they sell more 147 and 150 than 175, even though the match guys like it. There is more to the industry than precision rifles, and most guys who shoot those guns left the 308 a long time ago.

  • gunsandrockets

    Fascinating.

  • sauerquint

    It’s mentioned, with a link, in the ‘Rifleshooter’ post too. He’s obviously quite well informed on the subject.

  • Stephen

    Curses. I’ve badly wanted data for <16" barrels in .308. I assume this was not done due to the license requirement?

    • Bill

      That and ballistics by the inch does the handgun stuff.

      • Stephen

        Last I looked they only had .223. I want the same thing for a number of rifle cartridges (.308, 300blk, 6.5, 6.8, 5.45, etc)

  • Bill

    I’ve linked to all of those in my previous posts and my work isn’t duplicating any of those.

    • Sadler

      I intentionally looked through your posts on the barrel length X velocity tests, and they included none of the ones I mentioned, aside from BBTI. The other ones that they did include, I removed before posting.

      And yes your work is duplicating results. You’re losing 20-30 ft/s with a .308. Everyone who’s ever tested this or run it through a computer simulation gets this result, hence the general rule that you lose 25 ft/s per inch taken off.

      But again, I want to reiterate my last statement, because it seems you either missed it or didn’t bother expanding the post to read it. More data never hurts. I’m not criticizing you for giving people more data. I’m criticizing you for saying you’re the first to ever record this data.

      Again, more data never hurts.

      • Bill

        When did I say I was the first?

  • Jeff

    I would like to see the decibel rating of each barrel length also. I am confident 16 inches would be unpleasant.

    • noob

      can we crowdfund a research range with a saw and a lathe (for crowning the barrel) so we can see someone shoot groups at different lengths too?

      big gun mfgs have research ranges and that’s how they can say “at this length there is an optimum for velocity vs weight vs harmonics and accuracy”.

      It’s time we could rent time at such a range and find out for ourselves.

  • smartacus

    I like the speeds coming from that 26″ barrel

  • Zak B

    Something interesting I noticed is that for all the cartridges there seems to be a “sweet spot” in the standard deviation. It’s most noticeable in the 168gr, which seems to prefer 17-21 inch barrels.

    Anyone care to theorize why?

  • The Brigadier

    Muzzle velocity is one determination, but so is groupings at various distances. In the development of the .308 in the 1950’s, they found that flattest flight achieved was a combination of the 21″ barrel and the 168 grain bullet. That is why the DoD chose that combination for the official barrel length and the 168 gr cartridge for combat for the M14.

    The 147 gr cartridge is certainly faster because of its lightness, but it is not nearly as accurate at the 168 gr. The 147 gr cartridge was designated as the official training cartridge because the difference in weight of the two bullets resulted in a big savings for the million of rounds used in trainings after 1958 the year the M14 was chosen for our military.

    All the other NATO and SEATO allies chose the FAL that has the same barrel length and the same cartridge weights. Nowadays those numbers are around 15 billion rounds for training annually (at least before Obama gutted all of the training for all of our services) so the savings in lighter rounds for training is a substantial savings for the nation.