my first dive into the PCC pool was with a MechTech Glock format...the extension spring (think screen door) was immediately identified as a problem, as I was looking to produce the lightest recoiling carbine possible... I looked hard at a Granger catalog but just couldn't find what I was looking for, in addition to one of the pistol lowers had a tolerance problem, and would go full auto... I didn't even get a chance to run some cartridges across the chronograph...historical note... I did shoot PCC division for a little over a year with a blow back 9mm... using an NFA lower and NFA bolt with a 6.2oz rifle buffer and rifle length AR buffer tube and spring... I then switched to the CMMG radially delayed bolt..
a half dozen years ago I purchased a 16" pencil barrel, can't remember the manufacture... it did not produce the accuracy that I was looking for... with the better pencil barrels now available, and as I have a couple of spare uppers, I may look at a light weight carbine for a project... re: AR pistols, Tom has seen what I use for a buffer tube for my AR pistols... I think they are the quickest handling of any of my ARs, and would be a tough call not to grab one for any civil unrest ... if I lived where auto loading rifles were not legal, a 16" model 92 (not 94) in .357 mag would be my pick