.308 barrel length and other considerations



  • Ok everyone.
    I have a beautiful Bartlein barrel blank. Its in .30 caliber, M24 contour, 26 inches long and an absolute work of art.
    Next month I'm going to box it up and send it off to the gunsmith to have it installed on a surgeon 591 (which is equally beautiful.)

    The problem I'm having now is deciding what length I want it finished at. I've been doing my homework and the consensus seems to be I lose very little between 26 and 20 inches (and some even say 18 inches).

    With that said I'd like to get the opinion of the group.

    This rifle is intended as a training rifle. A .308 won't let me cheat the way a 6.5 or ballistically superior round will. I have to be ON with my wind and range call.

    As such, I intend to be shooting primarily 175 SMKs. So no 155's and long barrels.
    I don't expect to be walking around much with this gun, however I'll be shooting prone and positionally.
    I want the recoil to test my position. Bare muzzle.
    I realize I can push a handload to make up for any shortcomings of a shorter barrel

    Thanks for the advice. If I'm being honest I'm thinking of going for 24 (or as close as I can get) and cutting it back if it turns out its too long.



  • @ragnarnar I think you have a great plan.
    I'm running a 24" tite bore Bartlein M40 contour without a brake (can't use them in FTR). Mine weighs in at a little less than 18 pounds and is a pleasure to shoot.
    Your components should produce an exceptionally sweet shooter.



  • With factory 168's you will lose very little between 26" and 20". I bet the article you read was the tac ops article. When you handload you can take advantage of the extra inches more so than with factory loads...so it will make some difference. In my opinion if you are not running a suppressor then there is no reason not to go longer. 24" is a great compromise. I went 22.5" on my srs and according to ballistics am getting just over 2700 fps without a crazy hot load (44.5 varget/175 smk).

    How far do you plan on shooting?



  • @dddoo7

    I have some property about two hours away with unlimited range.

    I'll be working my way out but for the time being I expect most of the shooting to be done between 500 and 800 meters.



  • 308's tend to lose about 20fps per inch from 26 to 20. If I were you, I'd go with 20 or 22 inches. Keep it somewhat handy.



  • http://www.thetruthaboutguns.com/2013/10/daniel-zimmerman/the-truth-about-barrel-length-muzzle-velocity-and-accuracy/

    I found this link while I was doing more homework.

    I'm not overly concerned with the accuracy aspect, but there are some useful velocity figures about halfway down the page.

    According to the "study" 175 FGMM only loses about 75 fps from a 26 to 18 inch barrel. A 208 AMAX hand load only loses 100 fps in the same amount.



  • @ragnarnar said:

    According to the "study" 175 FGMM only loses about 75 fps from a 26 to 18 inch barrel. A 208 AMAX hand load only loses 100 fps in the same amount.

    I think anyone that goes into a 308 project expecting to lose 75fps from 26" down to 18" is going to be very disappointed. Most 18" 308's will top out at about 2550 with a 175SMK while most 26" barrels will be in the 2700fps range. 75fps is definitely very optimistic, and isn't the norm.



  • @orkan said:

    I think anyone that goes into a 308 project expecting to lose 75fps from 26" down to 18" is going to be very disappointed. Most 18" 308's will top out at about 2550 with a 175SMK while most 26" barrels will be in the 2700fps range. 75fps is definitely very optimistic, and isn't the norm.

    Do you happen to know the barrel length they use to publish the data on the box?
    I think I was told once it was 24 inches

    I have a box of federal 175 GMM in front of me and they're claiming only 2600 fps at the muzzle.

    Also this test comes pretty close to replicating the numbers from the test I posted above.
    http://rifleshooter.com/2014/12/308-winchester-7-62x51mm-nato-barrel-length-versus-velocity-28-to-16-5/

    I'm still leaning towards 24" at this point, so I have the option of shortening it as needed and the ability to throw heavier bullets a little better if the need or desire arises.



  • 26" is what most use. Some use longer.



  • I went and put masking tape on the barrel of my 25" .223 at various lengths trying to visualize the finished length of this .308.

    24" is way too long.
    22" is still long, but more manageable.
    20" looks good and is the same length as my deer rifle

    I'll probably go 22" just so I can fool with heavier bullets if I ever want to.



  • Unless I missed it somewhere one key piece of information that would help this decision would be the twist rate you're running. Could change things a little.



  • He mentioned 175SMK's, so that will be a 10 twist optimally.



  • @orkan said:

    He mentioned 175SMK's, so that will be a 10 twist optimally.

    You are correct.

    The barrel is a Bartlein M24 5R 10 twist.
    I talked to Travis @tscustoms today and because the reamer he'll be using to cut the chamber is suited for the 168-185 range I'm thinking I'll just split the difference and go with 21 inches.

    I don't want to lose the ability to play with 185's or 190's if I ever get the desire to do so.



  • I have a 24'' barrel and I like it.



  • Up front: no personal exp yet with this question.
    If you start at 26" you can shoot a lot before you have to cut 2" and rechamber due to loading hot and see erosion.



  • Re-chambering a shot out barrel is almost entirely a complete waste of time. Barrels do not wear out due to heat or friction... but rather the expansion/contraction due to the pressure wave riding behind the bullet. Thus if you cut off the chamber and start again, you will most certainly not get much benefit from it when weighed against the cost of re-chambering.



  • In addition to what Orkan said, I don't think that I'd want to carry around a 26" m24 profile barrel.

    Based on the stuff I posted above earlier in the thread, there's little point to having a barrel over 22 inches if you're going to shoot 175ish bullets.

    Also the blank is right now 26 inches long. After it gets chambered I don't think I could get much more than 24 actual inches of useable barrel out of it forward of the case mouth.



  • I just now got a good chronograph. My 22" 308 with 175 smk's is getting 2725 average. That is at 44.5 varget. I tested up to 44.9 and only had slight ejector swipe, but none at 44.5. I did not expect that much speed out of a short barrel.



  • That's faster than I would have expected as well. The M118LR makes only 2650.

    I might go with 20-21 just because I don't have an SRS and I'd like to keep overall length down.



  • Just as a point of reference, I happened to be taking measurements with my new 21.75" .308 today. Twenty-five rounds of FGMM 175gr averaged 2559 fps at 78degF, measured near the muzzle with a Magneto Speed v3.



  • @dddoo7 said:

    I just now got a good chronograph. My 22" 308 with 175 smk's is getting 2725 average. That is at 44.5 varget. I tested up to 44.9 and only had slight ejector swipe, but none at 44.5. I did not expect that much speed out of a short barrel.

    Benchmark barrels tend to run pretty quick. I've seen some slow ones from them, but it's fairly rare. That's why I never really shy away from doing 22's for a guy in a DT. ;)


 

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