556 pistol barrel length and gas system question

[Suicycle]

I'm considering building a short pistol and have seen mid length gas systems on 12.5" and though that was odd for dwell time. I'm leaning toward 10.3/10.5 unless a compelling reason for the 11.5 is made. Glanced around at BCM and a few other places and just assumed everything would be pistol gas system like the blackout is in the short barrels. This weapon probably won't see much use, but must run at all cost. It will see much trunk, truck, and case life since I can't carry a rifle EDC.

[kirkland]

5.56 barrels from 10.3 to 12.5 should be a carbine length gas system. You don't start getting into pistol length gas systems until you go shorter. I could be wrong, but I would think a 12.5 middy would be difficult to set up to run reliably, as there have been reports of even 14.5 middys not cycling weaker ammo. I personally just put together an 11.5 pistol with a colt 6933 upper, I chose the upper because it was available at a good price and I knew it would run.

[Suicycle]

Thanks for the info. I think it was just one shop that has mid length for short barrels and I thought right off it was a misprint.