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Sidearms & Scatterguns AR pistol barrel length, 10.5 or 11.5?

No advantage, either will work about equal. You won't see any advantage until you hit around 14.5" or longer.

Whatever you do, if you want to run a can on it, and make it look smooth, make sure your handguard is 1" shorter than the barrel's length.
 
Make sure the can manufacturer will warranty any issues with your barrel length as well.
 
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5.56 or 300BO? My first SBR was a 5.56, never built another. If you want short, 300BO makes a much nicer final product.

5.56 SBRs are loud as hell unsuppressed, don't suppress as well, lousy balistics, runs hot and your suppressor gets very hot.

300BO you can also drop a couple inch of length, I have two 8.3 and two 10.3, all good.
 
I have several 5.56 SBR's but in the OP's barrel length range, this 10.5" Noveske N4 is my favorite and also set it up as a "Master Key" just for fun. As mentioned little to be gained by swinging about another 4" of 5.56 barrel.

Also, went the other way by 6" with this 4.5" Rock River Arms 5.56, MagnetoSpeed V3 clocks it at 2250 fps (same as my FN 5.7 pistol) with Black Hills 50 gr TSX Optimized ammo; pretty small package. Unsupressed it is not any louder than FN5.7 pistol as one would expect with similar ballistics
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5.56 or 300BO? My first SBR was a 5.56, never built another. If you want short, 300BO makes a much nicer final product.

5.56 SBRs are loud as hell unsuppressed, don't suppress as well, lousy balistics, runs hot and your suppressor gets very hot.

300BO you can also drop a couple inch of length, I have two 8.3 and two 10.3, all good.
Thinking about 5.56. Not sure if I want to get one or not. On the fence between it and first can. Work related travel is picking up.
 
Thinking about 5.56. Not sure if I want to get one or not. On the fence between it and first can. Work related travel is picking up.
If you don't have a suppressor yet, I'd start there. It takes longer to get it than form 1 a SBR. Also, SBRs are stupid loud obnoxious unless you go pistol caliber or suppress.
 
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My vote is for the 11.5, or a 12.5. A little more velocity and dwell time, a little less wear and tear. Love mine
 
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My vote is for the 11.5, or a 12.5. A little more velocity and dwell time, a little less wear and tear. Love mine

Yep - the velocity difference isn't huge but every bit counts when there is already a lack of it. And reliability beats all - it's even more important than achieving the smallest possible gap between the handguard and suppressor!

Before determining the "best" length, determining the mission and choosing a cartridge is critical. Big difference between, say, a subsonic 300 AAC plinker and a SHTF 5.56.
 
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Yep - the velocity difference isn't huge but every bit counts when there is already a lack of it. And reliability beats all - it's even more important than achieving the smallest possible gap between the handguard and suppressor!

Before determining the "best" length, determining the mission and choosing a cartridge is critical. Big difference between, say, a subsonic 300 AAC plinker and a SHTF 5.56.
My all time favorite is my 12.5" 6.5 Grendel. Dosen't get stupid quiet like blackout subs, but suppresses well, and great energy, ballistics and precision.
 
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@gunsnjeeps - look in the AR pic thread at MSTNs posts on shorty ARs.
he does some nice detailed writing of parts (even a couple budget builds) and talks about speed and preferred loads for shorty 556 guns.

Form 1 a can and rock and roll.

Having both 10.5, 11.5, and 12.5, I think its personal choice and plan for the firearm.
Just buy parts according to plan.