From what I have read on several AR websites, the 5.56 caliber SBR or pistol upper seems to run best when in lengths 10.5" or longer. I know there are folks who have 7.5" ish ARs who claim great reliability, and that's fine. I am not here to dispute their claims nor start a pi$$ing contest over whether or not the shortest uppers in 5.56 can an do deliver reliability.
I am after more technical advice as to whether the 300BLK in a short (think 8.5 to 9.0") barrel might have the same issues as the 5.56 caliber uppers in an SBR or more especially, an AR pistol.
I am wanting to build an AR pistol and use both caliber uppers. I have decided on a 5.56 upper, but as for the 300BLK upper I am still looking at the characteristics involving the "shorter" of the short uppers in that caliber. I really like the 8.5 to 9.0" 300BLK uppers and I am hoping I can glean some solid info on using that length barrel in that caliber with regard to overall reliability. Also, whether gas impingement vs piston makes much difference in the short 300BLK upper's reliability, think cycling, ejection, etc..., not just the typical gas vs piston comparison.
I have AR carbines for training so this AR pistol is more of a hobby project and range toy, although one I want to depend upon if needed.
Thanks for any helpful insight. And yes, I did search but could not find the info for which I'm looking.
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