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Which barrel length for AR pistol? Login/Join 
Rule #1: Use enough gun
Picture of Bigboreshooter
posted
I see lots of uppers out there in 7.5", 8.5", and 10.5" bbl lengths. Which is best for a 5.56 AR pistol?



When a strong man, fully armed, guards his own house, his possessions are undisturbed. Luke 11:21


"Every nation in every region now has a decision to make.
Either you are with us, or you are with the terrorists." -- George W. Bush

 
Posts: 13753 | Location: Birmingham, Alabama | Registered: February 25, 2009Reply With QuoteReport This Post
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Picture of CandyMan.45
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Ideally for best ballistic performance... 10.5-11.5" is optimal. Versus what you scarce in concealability and noise going shorter.
 
Posts: 984 | Location: The Edge of Nowhere... | Registered: April 05, 2013Reply With QuoteReport This Post
Sigless in
Indiana
Picture of IndianaBoy
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Below 10.5 (10.3 for some Colt uppers), muzzle velocity falls off tremendously and blast goes way up. I opted for an 11.5 myself, I think 10.5 would have been fine as well. 11.5 gained me a bit of velocity and should be a bit easier on my silencer.

I haven't personally owned a pistol length gas system but I have read that they are more finicky to get running right with a less forgiving window of proper operation.
 
Posts: 12972 | Location: The Edge of the Ozarks | Registered: December 04, 2003Reply With QuoteReport This Post
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Picture of Yanert98
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I found 10.5 and above to be the most reliable.


----------------------------------
The first lesson of economics is scarcity: there is never enough of anything to fully satisfy all those who want it. The first lesson of politics is to disregard the first lesson of economics. - Thomas Sowell
 
Posts: 2165 | Location: Migrating with the Seasons | Registered: September 26, 2007Reply With QuoteReport This Post
Fighting the good fight
Picture of RogueJSK
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Yep. Unless you have some compelling reason to need a shorter barrel (for specific concealment purposes, or the like), 10.5+ is the way to go.
 
Posts: 19913 | Location: Northwest Arkansas | Registered: January 06, 2008Reply With QuoteReport This Post
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I took a 16” CHF DD midlength barrel and cut it to 12.5” per Dave’s recommendation at Adco. Drilled and pinned on a lopro Geissele gas block. It’s not appreciably longer than my 11.5” SBR but I get no gas to the face and it shoots very reliably. Shooting 77gr IMI SMK, it’s very soft shooting.
 
Posts: 205 | Registered: March 18, 2013Reply With QuoteReport This Post
Rule #1: Use enough gun
Picture of Bigboreshooter
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OK, the consensus seems to be 10.5". With a carbine length gas system, are there any timing issues with the muzzle being in such close proximity to the gas block? Similar to the original Dissipators' (rifle barrel cut to 16" w/rifle length gas system) timing issues for this reason.



When a strong man, fully armed, guards his own house, his possessions are undisturbed. Luke 11:21


"Every nation in every region now has a decision to make.
Either you are with us, or you are with the terrorists." -- George W. Bush

 
Posts: 13753 | Location: Birmingham, Alabama | Registered: February 25, 2009Reply With QuoteReport This Post
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I went with a 7.5, but I only did it because it is a fun range toy. I have plenty of other guns to "Go To" when the time comes. I would go 10.5 or 11.5 for anything serious.


#1 of 2
 
Posts: 256 | Location: VA | Registered: April 06, 2007Reply With QuoteReport This Post
My hypocrisy goes only so far
Picture of GrumpyBiker
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MARSOC is running 10.3" barreled MK18s effectively.
My Buddy commands 2nd Raiders Bn & I been picked his brain prior to my pistol builds.
Based on that I went with 10.5" for 3 of my 4 AR pistols (7.5" is my 4th pistol ) .
No functioning issues at all.







U.S.M.C.
VFW-8054
III%

"He's a Mean Motor Scooter & a Bad Go Getter !"



 
Posts: 5701 | Location: Central,Ohio | Registered: December 28, 2008Reply With QuoteReport This Post
Plowing straight ahead come what may
Picture of Bisleyblackhawk
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I've had zero issues with the 10.5" PSA upper on my pistol build using a variety of ammo, mostly AE 55 grain, but my last range time I ran through 5 magazines of the Wolf steel case stuff without a hiccup...it is noticeably louder than the longer barrels though, which is a non issue.


********************************************************

"we've gotta roll with the punches, learn to play all of our hunches
Making the best of what ever comes our way
Forget that blind ambition and learn to trust your intuition
Plowing straight ahead come what may
And theres a cowboy in the jungle"
Jimmy Buffet
 
Posts: 7703 | Location: Southeast Tennessee...not far above my homestate Georgia | Registered: March 10, 2010Reply With QuoteReport This Post
No ethanol!
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As said above, in 5.56 go w/ longer barrel. I do have a 7.5" pistol, and the the muzzle blast is almost as fun as the annoyance. The 3' fireball at dusk is fun, impractical, and louder than it should be.


------------------
The plural of anecdote is not data. -Frank Kotsonis
 
Posts: 1071 | Location: Berks Co PA | Registered: December 20, 2006Reply With QuoteReport This Post
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Picture of kimberkid
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If you are going to suppress it or use a piston conversion a lot of manufacturers will say anything less than 10.5 or 11.5 will void the warranty ... I tried putting a older Osprey Defense piston system on a 10.5” and it would short stroke, when I called they said the 5.56 needed to be 11.5 or longer ... it worked with my suppressor but my C3 dealer said it would void the warranty ... lesson learned Frown


If you really want something you'll find a way ...
... if you don't you'll find an excuse.

I'm really not a "kid" anymore ... but I haven't grown up yet either Wink
 
Posts: 4337 | Registered: January 11, 2007Reply With QuoteReport This Post
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I went 11.5


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Posts: 6797 | Location: One step ahead of you | Registered: February 10, 2009Reply With QuoteReport This Post
Sigless in
Indiana
Picture of IndianaBoy
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quote:
Originally posted by Bigboreshooter:
OK, the consensus seems to be 10.5". With a carbine length gas system, are there any timing issues with the muzzle being in such close proximity to the gas block? Similar to the original Dissipators' (rifle barrel cut to 16" w/rifle length gas system) timing issues for this reason.



It will depend on a few factors:

Size of your gas port.

Ammo.

Weight of your buffer.



I have an H3 in my 11.5 that I shoot with a silencer attached virtually 100% of the time.


It runs with Wolf, (the WPA stuff, not the black box), and all the brass cased ammo I have shot in it.


Who makes your barrel will determine the size of the gas port.

Colt and Daniel Defense generally port theirs to run with proper M193. Other vendors want reliability with whatever commercial ammo may wind up in the gun, so their ports will be a bit larger.

This can be mitigated with an adjustable gas block if you plan to run suppressed.
 
Posts: 12972 | Location: The Edge of the Ozarks | Registered: December 04, 2003Reply With QuoteReport This Post
Telecom Ronin
Picture of dewhorse
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In 5.56 there is a significant velocity gain going from 10.5" to 11.5" so I went with a 11.5" for my SBR.

That being said it depends on your intended use, all around use I would say 11.5".

I am building a PDW to use as a truck pistol, it will have a 8.5" barrel with a krink FH. depending on ammo ( 55gr TSX or GD) it should be good out to 75m and very handy if I had to use it from the cab.

If you are looking at 9mm or 300blk I would go with 8.5", 6.8spc I would stay around 12".
 
Posts: 6443 | Location: Back in DFW ....hopefully to stay | Registered: February 12, 2004Reply With QuoteReport This Post
My hypocrisy goes only so far
Picture of GrumpyBiker
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The velocity loss of 5.56 from a short barrel is why I built a brace of 300Blk pistols for PD use.
Just a better choice for that role. YMMV







U.S.M.C.
VFW-8054
III%

"He's a Mean Motor Scooter & a Bad Go Getter !"



 
Posts: 5701 | Location: Central,Ohio | Registered: December 28, 2008Reply With QuoteReport This Post
I've got mental
blue balls now
Picture of tlbailey1
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Do you have a preference to handguard? Or do you know what rail you want to use? This was what I based my decision off.


_____________________________________________
Welcome to Idaho, now take a wolf and go home!
 
Posts: 6769 | Location: Idaho | Registered: November 20, 2007Reply With QuoteReport This Post
hello darkness
my old friend
Picture of gw3971
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I built this 7.5" fun gun and love it. I have a couple of 10.5" sbr's and they are great too.

 
Posts: 5842 | Location: Riverton , Utah | Registered: June 19, 2007Reply With QuoteReport This Post
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I had a 6.5" or 7" barrel (I can't remember which now), but prefer 10.5".
 
Posts: 430 | Location: WV | Registered: May 30, 2013Reply With QuoteReport This Post
sick puppy
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Like others, I have a 10.3 and an 11.5. Both have been 100% reliable.


☣Biohazard☣
 
Posts: 6736 | Location: Alpine, Ut | Registered: February 17, 2010Reply With QuoteReport This Post
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