What's the best (most reliable) ar-15 pistol barrel length?

Technical discussions relating to specific firearms.

What's the best (most reliable) ar-15 pistol barrel length?

Postby newportri » Wed Sep 17, 2014 4:36 pm

After checking out a ar-15 pistol last night, I would like to build one myself in .223. What is considered the standard (best) in barrel length and gas system length?
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Re: What's the best (most reliable) ar-15 pistol barrel leng

Postby jcat » Wed Sep 17, 2014 7:29 pm

The gas system is most important in an AR pistol. Anything under about 10" needs pistol length gas system, anything above that should use Carbine gas.

In .223/5.56, most people run 7.5" if unsuppressed, 11.5" if suppressed. One downside I've heard of with the 7.5's is they can potentially rip rims off of cases due to the pressure spike from the short gas system.

One thing to consider is your intended purpose. Shortening the barrel will reduce velocities significantly. The difference between a 10.5" and 7.5" barrel with 55gr XM193 ammo is just south of 400fps, or close to 15%.

Chart for reference:

BBL___ 77 gr__M855 62 gr__XM193 55 gr
7.5"_____2053________2244________2364
10.5"____2363________2639________2755
14.5"____2576________2861________2984
16"_____2669________2938________3075
20"_____2818________3061________3254


Now if you decide to go 300blk, anything is fair game as even longer barrels use pistol length gas for the most part.
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Re: What's the best (most reliable) ar-15 pistol barrel leng

Postby newportri » Thu Sep 18, 2014 1:12 am

I was thinking around 10" would be good. 7.5" seems really short to me, but I don't have any experience with them. Is there a huge difference in noise and muzzle flash between the 7.5" and 10-11" barrels?

I think I would just stay with .223 for now since I don't really like to have too many different calibers.
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Re: What's the best (most reliable) ar-15 pistol barrel leng

Postby jcat » Fri Sep 19, 2014 12:43 pm

newportri wrote:I was thinking around 10" would be good. 7.5" seems really short to me, but I don't have any experience with them. Is there a huge difference in noise and muzzle flash between the 7.5" and 10-11" barrels?

I think I would just stay with .223 for now since I don't really like to have too many different calibers.


Muzzle flash will greatly depend on your muzzle device. There are a lot of options out there that will virtually eliminate muzzle flash. The A2 doesn't do a bad job of it, but you can do better.

Sound, forget about sound when going that short haha. We're cursed to not be allowed to own suppressors so I doubt there will be any appreciable difference in sound. They'll both be F'in loud.

I've been going through the same considerations on my 300 blackout pistol/faux SBR build since the upper I got didn't come with a muzzle device. I'm leaning toward the Troy Claymore brake both for aesthetics and because it's a linear compensator, directing flash, noise and more importantly concussive blast forward away from the shooter and toward whatever I'm shooting at. It won't make it ear safe or anything indoors, but it should help reduce flash and at least make it a little more pleasant for me and those around me when shooting it. I'm probably going to put together a 5.56 shorty upper to have so I can swap back and forth on the pistol lower in case 300blk gets too expensive to shoot :D
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Re: What's the best (most reliable) ar-15 pistol barrel leng

Postby a1983 » Fri Sep 19, 2014 1:31 pm

Hmm... pistol build with a 20" barrel?

CHALLENGE ACCEPTED ;)
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Re: What's the best (most reliable) ar-15 pistol barrel leng

Postby jcat » Fri Sep 19, 2014 1:33 pm

a1983 wrote:Hmm... pistol build with a 20" barrel?

CHALLENGE ACCEPTED ;)


that would be possibly the single most useless weapon ever conceived :lol:

Would be even better with one of the RRA uppers that don't need a buffer tube
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Re: What's the best (most reliable) ar-15 pistol barrel leng

Postby newportri » Fri Sep 19, 2014 6:35 pm

I like those RRA without the buffer tube, but I was also thinking it would be nice to have a faux SBR (if I get a Sig arm brace).
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Re: What's the best (most reliable) ar-15 pistol barrel leng

Postby jcat » Fri Sep 19, 2014 7:31 pm

newportri wrote:I like those RRA without the buffer tube, but I was also thinking it would be nice to have a faux SBR (if I get a Sig arm brace).


Worth every penny. I'll have to snap a picture of mine with the brace on it, and if you do decide to go that route I can recommend KAK's sig brace specific buffer tube, or another one that's in the works from Odinworks called the PTVPR which has a lot of cool stuff specifically engineered for the sig brace.

Truthfully, for the money of the RRA LAR pistol, I'd prefer a Sig P556, but I'm biased :mrgreen:

I like my 10.5" barrel. I could in theory go to a 7.5" and not really lose much velocity on 300blk, but 7.5" would put the end of the muzzle device flush with my handguard which I don't want to change. With the 10.5" and the Sig brace it's a considerable amount more maneuverable than a 16" AR like I had before, and way lighter than my 556.

I think the 556 may get converted to more of a DMR type rifle now that I built this faux-SBR.
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Re: What's the best (most reliable) ar-15 pistol barrel leng

Postby newportri » Fri Sep 19, 2014 11:40 pm

Hmm, I didn't know Sig made one like that..
http://www.sigsauer.com/CatalogProductDetails/p556-pistol.aspx
It's pretty neat, but I don't like the handguard. It's strange I don't see it when I search for pistols on Sigs website (I would like to see if they have different models of it), but Google finds it.
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Re: What's the best (most reliable) ar-15 pistol barrel leng

Postby newportri » Mon Sep 22, 2014 1:03 am

I like this barrel by Daniel Defense:
http://www.midwayusa.com/product/2684151347/daniel-defense-barrel-ar-15-pistol-556x45mm-nato-government-contour-1-in-7-twist-hammer-forged-chrome-lined-chrome-moly-matte-pre-ban?cm_vc=ProductFinding
It's a little expensive, so I am also looking at an AR Stoner:
http://www.midwayusa.com/product/193385/ar-stoner-barrel-ar-15-pistol-556x45mm-nato-medium-contour-1-in-7-twist-105-chrome-moly-melonite-coated?cm_vc=ProductFinding
I assume the quality is not the same, but is it worth the extra money for the DD? I am not planning on shooting anything at 600 yards, and I will probably by limited to shooting maximum 200 yards.
....the right to keep and bear arms, shall not be infringed.
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