Shortest reasonable Barrel length 308AR

[Benito]

There are some great sources out there for decisions on barrel length, including specifically for .308.
I went with a 16". Lengths above that will squeeze every last bit of velocity out of the cartridge, but it's up to you and your needs/wants if that juice is worth the added weight and overall length.
Going shorter that 16" will increase muzzle blast quite a bit.
With a semi-auto, there are cycling dynamics/timing issues to consider, which I am not qualified to discuss, that are not present in bolt guns.

http://rifleshooter.com/2014/12/308-...ty-28-to-16-5/

http://www.thetruthaboutguns.com/201...-and-accuracy/

[LS1POWERED]

Taken from an archived thread on the other site.


150g HPBT win 748 loaded to chamber pressure of 56.4k, a warm load.


16" barrel, 12k PSI, 97% powder burn
2623 fps with 2291 lb/ft energy.*


12" barrel 16.7k PSI, 94% powder burn.
2417 fps with 1946 lb/ft energy.


10" barrel 20.5k PSI, 91% powder burn.*
2273 fps with 1720 lb/ft energy.


8" barrel 26k psi with 87% powder burn
2080 fps with 1441 lb/ft energy.*


So either barrel length you are looking at will be effective, not loosing a ton of velocity going to a 12". Heck even the 8" barrel is comparable to a 16" 300 blackout or 7.62x39. Plus short guns are more fun.

[the_1iviper]

i have a 12.5" 308 that's a great shooter. it's no more of a flamethrower/hand cannon than any of my 5.56 sbr's. the gun and ammo are much heavier than it's smaller brother but it also makes bigger holes through heavier/thicker objects than 5.56 will. i mostly shoot m80 ball for general blasting but i've found that mk319 mod0 does really well out of a short 308. trying to push the heavier bullets at distance is where you would want that extra couple of inches of barrel imho. i think lmt and h&k and a few others have hit the sweet spot on a short 308 with their 13.5" barreled offerings.

[Failure2Stop]

With modern ammo and contemporary 7.62 semi-auto technology, I'm good down to 14.5, if the range envelope is inside 600 meters.
Go to a 1:8 or faster twist, and that stretches a bit, but the trans-sonic range is what it is.
With anything less than 14.5 you start to get really close to .300 Blk performance, at a noticeable increase in burden with 2/3 ammo capacity.
I personally like 16" 7.62 as it covers a lot of ground acceptably, not outstandingly.
Reducing MV also gets into whole new areas of zeroing concepts with a 7.62. 16" .308 guns already benefit from a departure in conventional zeroing approaches (I'm going to do a little write-up on that soon).
The difference in wind when going from a 20" to a 16" is noticeable, losing even more starts to get annoying at around 300.

Really it all comes down to meeting expectation and requirements. If you know what you are getting into, I'm not going to tell you not to do it.

[Amur]

With modern ammo and contemporary 7.62 semi-auto technology, I'm good down to 14.5, if the range envelope is inside 600 meters.
Go to a 1:8 or faster twist, and that stretches a bit, but the trans-sonic range is what it is.
With anything less than 14.5 you start to get really close to .300 Blk performance, at a noticeable increase in burden with 2/3 ammo capacity.
I personally like 16" 7.62 as it covers a lot of ground acceptably, not outstandingly.
Reducing MV also gets into whole new areas of zeroing concepts with a 7.62. 16" .308 guns already benefit from a departure in conventional zeroing approaches (I'm going to do a little write-up on that soon).
The difference in wind when going from a 20" to a 16" is noticeable, losing even more starts to get annoying at around 300.

Really it all comes down to meeting expectation and requirements. If you know what you are getting into, I'm not going to tell you not to do it.

Jack, how about you get me one of those 14.5" DIrect attach DSR kac sr25 and we just call it a day.

That seems like the rig right there from 0-600 for anything you want to do.

[polydeuces]

The key issue here, as always indeed, expectations and requirements.
Knowing full and well that less than 16 is getting into an area where compromises will be made at longer ranges.
Less than 13.5 - 14 and things get a bit more 'experimental' not just range but performance.
Guess it's all about the doing it.

See - here's the thing. With AR15 we have every (in)conceivable length.
Not so with AR308.
So we're simply going to have to do it ourselves and share the warmth. Simple as that.

IF.... I had a more 'dynamic" budget, I'd start with a 16" barrel, test, chop it to 14 and compare them.
One thing I've learned about the AR platform is (speaking for myself) with quality components it usually out-performs me, and is capable of things its said not to be.

Clearly a 16 will be GTG - then seeing a decent barrel will set me back 'only' about $140, and it won't be a crime beating it up a bit.
Dedicated receiver (aero) ~$95. Shipping barrel to adco, chop to 14.5 crown n thread another ~$60.

It's just numbers right? And I can't take it with me - none of it. Keep talking, I'm almost there.

[Stengun]

Howdy,

Very interesting thread.

Most of the "old school" reloading manuals usually suggest 25 ft/sec per inch of barrel for loads below 3,000 ft/sec and about 30 ft/sec for loads above 3,000 ft/sec.

As clearly shown by the test on the link someone provided that factory loads designed to work best in a 24" barrel had did their thing by 28".

For a barrel longer that 26" a handloaded would use a slower powder and for a shorter barrel, especially 16" or less a faster powder would provide better velocity than a powder that would function best in a 24" barrel.

Also for a short barrel a faster powder would create a smaller fireball blast and muzzle blast.

Paul