I am looking to put together a Pistol AR-15 with plans of filing the paperwork for it to be a SBR in the furture. I am looking at 10.5", 11.5" and 12.5" barrel lengths. Reliability is the most important thing to me then the fact that I can break the upper and lower down into a very compact package. My question is what barrel length tends to be the most reliable while still giving you good ballistics from the 5.56 cartridge? I have been looking at the 12.5" barrels but I would like the advice and opinions of others that know more about these things then I do.
I have never owned a pistol length AR barrel, so I can’t say which is best, but I would want the longest barrel I could get, and still fit within the limits of my needs. I personally would not want to go shorter than 11.5.
I’m glad you’re looking at barrels longer than 10.5" for starters. I’ll tell you that I only owned 1 AR pistol upper and I sold it pretty quickly after I got it. Granted, it was from a POS company and required my having to replace a bolt carrier group because their customer service refused to do anything to help me out (poor machining, bolt would not rotate when extracting or going into battery). I also found that after replacing the bolt, I would have some issues when the gun would begin to get warm. It was an 8.5" barrel with a standard A2 birdcage. I ruled out magazine and ammo since I primarily shoot 55 grain Freedom Munitions and a mix of American Eagle/Federal 5.56mm through my AR and other buddies (Smith and Wesson M&P 15 and a Ruger SR-556). I don’t run much .223 and I can’t imagine much of a difference reliability wise for the pistol.
If I wanted to try it again, I’ve read that the 10.5" is the shortest you would want to go in order to have a reliable system. I can link articles to those articles, but I’m sure you’d rather get a consumers opinion over a typical review (that’s why you’re here). Don’t go cheap, get a quality barrel/upper and don’t make the same mistake I did with the 8.5". I hope this at least gets the conversations started.
Note: Make sure you have your ear protection, these things are loud!!!
Up to you on getting an SBR. I would get the longest barrel you feel comfortable with. There will be less muzzle flash and noise. Performance with 5.56 really starts dropping when you get shorter than 14.5" but as long as you know and understand the limitations, you can make it work and work well. I believe some of the shorter barrels have a shorter than carbine length gas tube. The shorter the gas tube, the hotter the gases are going in to the tube and into your BCG. The main concern with that is accelerated erosion at the gas port. Then there is the louder bark as the barrel gets shorter and more muzzle blast from unburnt powder exiting the muzzle.