Does shortening a barrell compromise performance?

[1Fastrider]

I'm building a DPMS style .308 AR. The shortest barrell I've seen is 16" and I'd prefer it to be 12" or 14". Can I just get any premade upper or barrell and find a gunsmith to chop it off, thread it, and put a compensator on it? Is there other work that would need to be done?

[croc4]

depends

whats your definition of performance?

If its balistic performance, then yes, you will loose fps with a shorter barrel vs a longer one. Less fps, your sacrificing long range performance (generally).

you also gain noise 'performance' its going to be a lot louder and a lot more muzzle flash as the powder will have less time to completely burn in the barrel.

Now if your talking about some form of tactical performance, then I guess you would. I'm not a tactical type shooter, so I'll leave that for someone else to comment on.


croc4

[TATER313]

I believe it has to have an OAL of 16", and compensator will have to be pinned and welded.

[G-forceJunkie]

Yes, it does. The shorter the barrel on a .308, the slower the bullet is going to go. Also as mentioned, 16" is the legal, minimum length.

[1Fastrider]

I'm putting it on an 80% lower (pistol) so the length is good but thanks for noting that. I probably worded the question poorly as I don't plan on shooting past say 200 yards.

So I have a follow up: Is there a certain point in the barrell where it should be cut? ex: at 14 inches is the correct length so that the bullet is doing xyz? sorry for the vague questions and thanks all for the comments.

[LCU1670]

Barrel length, twist rate and weight of bullet is the major factor. Next: barrel harmonics. So, its a matter of balancing all of those.

[xrayoneone]

16" is probably the shortest you want to go with a 308. The muzzle blast will be horrible and performance will suffer. The 308 is not a cqb round. If you want a short 30 cal I would look at the 300 AAC. It is optimized for short barrels, the muzzle blast is negligible, and components are much cheaper and easier to obtain, but if you chop a barrel I wouldn't go less than 14". Anything shorter probably wouldn't run right. Look up gas port sizes and dwell time.

[spamsucker]

Going with such a short barrel you'll be building a noise and flash generator that wastes tons of powder and delivers garbage ballistic performance for the cost of each trigger pull. It'll eat expensive ammo and not do anything but annoy people in the adjoining lane at the range.

Apart from the terrible ballistics, shortening the barrel that much on an AR platform will require shortening the gas system which will put the gas port in a VERY high pressure area of the barrel and will probably cause all manner of problems.

[1Fastrider]

Thanks all. I've been looking at a 300 build also so maybe I'll just go that route and nix the .308 idea. I just have the lower so far so nothing is set in stone yet.

[kcstott]

and not do anything but annoy people in the adjoining lane at the range.

That's if you go to a public range.
i don't need some drill instructor wanna be range master trying to tell me how to be safe. I' haven't been to an public range in years.

But I do agree with the total waste of money on ammo for a novelty.
I have a Novelty it's anAK pistol it's fun to shoot but thats it. It servers only two purposes One is to be fun to shoot, Two is to piss off every POS liberal gun grabber out there as this thing had to pass through SSE to be legal. I thumb my nose at your BS laws and fart in your general direction.

[1Fastrider]

I've been checkin out the AR Pistol thread. Couple mentions of building whatever would piss off a liberal. Must be a trend that I have to get in on

[0nTarg3t]

That's if you go to a public range.
i don't need some drill instructor wanna be range master trying to tell me how to be safe. I' haven't been to an public range in years.

But I do agree with the total waste of money on ammo for a novelty.
I have a Novelty it's anAK pistol it's fun to shoot but thats it. It servers only two purposes One is to be fun to shoot, Two is to piss off every POS liberal gun grabber out there as this thing had to pass through SSE to be legal. I thumb my nose at your BS laws and fart in your general direction.

lol +1

[joelogic]

I'm putting it on an 80% lower (pistol) so the length is good but thanks for noting that. I probably worded the question poorly as I don't plan on shooting past say 200 yards.

You are going to shoot an LR308 pistol at 200 yards? That would be pretty hard, IMHO. Plus a ton of muzzle blast.

[JDay]

I believe it has to have an OAL of 16", and compensator will have to be pinned and welded.

It's 16" from breechface to muzzle iirc.

[hermosabeach]

These guys have chopped a few barrels

http://www.ballisticsbytheinch.com/calibers.html

To simplify - why did you go with .308?

As you slow the bullet, many calibers blur

KE= 1/2mass x velocity squared
Momentum = mass x velocity

So if the .308 slows way down... What do you have??? Besides a rock concert- flashes of light and blasts of sound

If you go slow, you would save money with the 7.62x 39

Also I have no idea what rate of twist you would need in a short .308 barrel
(The krink is a faster twist than the standard 16" barrel)

Info that might help
150 gr HPBT Win 748 loaded to a chamber pressure of 56.4K PSI WARM load 45 gr NOT a starting load. I chose 748 as the powder as it is most like NATO powder.

26" = 2918 FPS MP= 6.6K PSI ––99.6 % powder burnt -2836 ft/lbs
24" = 2873 FPS MP= 7.4K PSI ––––––––––––––––––––––––––––2750 ft/lbs
22" = 2823 FPS MP= 8.2K PSI ––––––––––––––––––––––––––––2655 ft/lbs
20" = 2766 FPS MP= 9.2K PSI ––98.7 % powder burnt -2548 ft/lbs
18" = 2700 FPS MP= 10.5K PSI ––––––––––––––––––––––––––––2428 ft/lbs
16" = 2623 FPS MP= 12.0K PSI -97% powder burnt ––––2291 ft/lbs
14" = 2531 FPS MP= 14.0K PSI ––––––––––––––––––––––––––2133 ft/lbs
12" = 2417 FPS MP= 16.7K PSI -94% powder burnt ––1946 ft/lbs
10" = 2273 FPS MP= 20.5K PSI ––––––––––––––––––––––––––1721 ft/lbs
8.0"= 2080 FPS MP= 26.0K PSI -87% powder burnt. -1441 ft/lbs
6.0"= 1800 FPS MP= 34.1K PSI -79.4% powder burnt -1080 ft lbs