20 vs. 22 inch barrel in .308
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dh1633pm
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citizenconn
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Regarding ARs: Get the 20". Slight improvement in all areas over 18" and significant over 16" unless you like making a big fireball (I do). I do have several 24" and the only real advantage is some velocity increase, which I got them for specifically for target shooting past 800 yards. The 24" are too heavy to carry very far. 20" burns all the powder in both handloads and factory.
Bolt guns: I have 16" heavy barrel, 20" medium barrel, 22" medium tapered, 24" heavy barrel on law enforcement sniper rifle. I prefer the 22" medium tapered in an MDT chassis because it balances better plus is a great carry option for hunting. Again, 20" burns all the powder. I only get the 24" ones for velocity increase for target shooting. YMMV.
Bolt guns: I have 16" heavy barrel, 20" medium barrel, 22" medium tapered, 24" heavy barrel on law enforcement sniper rifle. I prefer the 22" medium tapered in an MDT chassis because it balances better plus is a great carry option for hunting. Again, 20" burns all the powder. I only get the 24" ones for velocity increase for target shooting. YMMV.
C-grunt
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Like citizenconn said, you do see a velocity increase going from 20 inches to 22 or 24, but it's not significant. If you are using the rifle for long distance target shooting it will give you another maybe 100 yards of supersonic flight. My custom 308 I had built has a 20 inch barrel and it shot fine out to 1040 yards. It'll see 1300 by the end of the year and I'll give a mile a try too.
All of the powder burns within 6-8". But longer barrels give more time for the bullet to accelerate before leaving the muzzle. If we use 24" as standard, most magnum cartridges will see 25-35 fps less velocity as the barrel is cut shorter. Others like 308 may only see 10-15 fps for each inch the barrel is cut shorter. But that only applies if you use the same barrel, same loads, and only cut that barrel down shorter as you go.
At least for a few inches on either side of 24". As you get below 20" you see bigger losses as each inch is cut off. If using a barrel longer than 24" the gains get smaller and smaller as you get longer.
When comparing two different barrels all bets are off. Even when they are the same length a difference of 25-50 fps is very common and 75-125 fps isn't unheard of. I have 4 rifles in 308. The fastest barrel is the one that is 20" long. It shoots faster than the other two that are 22", and there is a 20-30 fps difference between the two with 22" barrels. The difference is small, but real. The 18" barrel is the slowest. I have two 30-06 rifles, both with 22" barrels. The Winchester is 60-90 fps faster than the Remington depending on the load.
IMO I don't have a problem with a 20" barrel on a 308. Below 20" and you do see enough velocity loss to matter and noise becomes a factor. But for thick brush hunting they can be handy and you don't need the velocity up close. And if you think a 22" or even 24" barrel looks and balances better then let that decide for you. There isn't much difference in MV either way.
FL-NC
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How does one know if a powder burn is complete? ALSO, Larue OBR rifles with 16" barrels have been used to win the USASOC sniper match at Ft Bragg a couple of times. It is amazing what can be done at distance when a shooter knows the muzzle velocity of his specific rifle with his selected ammunition and has the ability to calculate relevant information with ballistic software using an old PDA/palm pilot.
25-20 WCF
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How about some actual data instead of rules of thumb or wild guesses or “I read it on the internet forum”?
From G&A, July 1989
.308 Winchester, Hornady Factory ammo, 165-grain bullet
Same barrel cut off at the following lengths and chronographed:
22” - 2674 fps
21” - 2636 fps
20” - 2617 fps
19” - 2595 fps
18.5” - 2598 fps
No significant velocity loss was seen below 22” as far as the test went - but this is a single barrel and load. Had the author chronographed 40 shots at each length we’d have even better data. If you think that 50 to 75 fps is significant in any way, well perhaps a 24” or 26” barrel should be in your future.
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From G&A, July 1989
.308 Winchester, Hornady Factory ammo, 165-grain bullet
Same barrel cut off at the following lengths and chronographed:
22” - 2674 fps
21” - 2636 fps
20” - 2617 fps
19” - 2595 fps
18.5” - 2598 fps
No significant velocity loss was seen below 22” as far as the test went - but this is a single barrel and load. Had the author chronographed 40 shots at each length we’d have even better data. If you think that 50 to 75 fps is significant in any way, well perhaps a 24” or 26” barrel should be in your future.
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Depending of the propellant complete burn is accomplished between 9 and 15 inches from the breech.
For M80 ball with WC846 it's 9 inches, with IMR 3031 10.5 inches.
If you have a pressure vs time curve, you can plot it on a log graph and where the curve becomes a straight line, combustion is complete and the expansion is adiabatic (no more heat being added).
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The US Army decided on 22" for a combination of performance and muzzle flash. The basic physics haven't changed. Maybe flash suppressors have.
Depending on bullet weight, type, cartridge brand, etc, you generally won't see any more than 30 to 60 fps loss in velocity going from 22" barrel to 20" in.308. And in most cases you'll have complete powder burn with either. Not enough to lose sleep over.
That being said, there are so many varieties of factory .308 and powders for handloading available, you may see a greater spread in velocities in some cases.
A 22" barrel for a bolt gun is the sweet spot for me in.308 and a few other calibers. 18" to 20" is scout rifle territory, and that's probably what I'd do with a barrel length in that range.
That being said, there are so many varieties of factory .308 and powders for handloading available, you may see a greater spread in velocities in some cases.
A 22" barrel for a bolt gun is the sweet spot for me in.308 and a few other calibers. 18" to 20" is scout rifle territory, and that's probably what I'd do with a barrel length in that range.
Chuck R.
Member
Everything is a compromise.
I have a .308 in a 19" barrel and a .260 Rem in a 20" barrel. I don't notice any muzzle flash with either and that's at legal shooting time both AM and P(1/2hr before and after sunrise/sunset).
The loss in velocity when measured in energy and drop, is pretty insignificant. At the distances most big game is taken, it's even less significant. I gladly give up a little performance to gain compactness and handling characteristics.
I have a .308 in a 19" barrel and a .260 Rem in a 20" barrel. I don't notice any muzzle flash with either and that's at legal shooting time both AM and P(1/2hr before and after sunrise/sunset).
The loss in velocity when measured in energy and drop, is pretty insignificant. At the distances most big game is taken, it's even less significant. I gladly give up a little performance to gain compactness and handling characteristics.
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