Does anyone know what size the gas port is on psa’s 10.5 premium uppers? I have one, runs like a champ on both my pistol lowers, and recently built another 10.5 also with an FN CL barrel, and a 20 inch with a cheap little Del-Ton chome lined heavy barrel. The 20 inch also runs like an absolute dream despite the cheap barrel but GOD HELP ME my 10.5 wont run for piss.
Gas block is lined up fine, Ive swapped lowers and buffers with my functioning PSA pistol and it still wont reliable cycle. It behaves as if its undergassed. Theres just enough to cycle the bolt but not always enough to extract, or if it extracts it wont pick up the next round. Only thing i can think of left is I got a barrel with a slightly undersized small Gas port.
Its on a psa pistol lower, so im assuming a standard 3oz buffer and spring. Again my other pre assembled upper runs just fine on it so it has to be a port issue. Ive ruled out just about everything else.
As far as ammo whinchester white box, tula and a brand of .223 Remington i cant quite recall atm. The 5.56 seems to be the only ammo that will -nearly- cycle and usually results in a ftf and a round jammed on my feed ramps.
Those barrels are made for 5.56, and some 223 ammo (like the white box win) are known to be on the weak side. Fwiw I have a 10.5 FN chf barrel and I only use 5.56 ammo in it.
So your upper that isn’t working is one you built? Unfortunately that is not a PSA issue then. I would suggest measuring the gas block and going from there. You may need to have a gun Smith open it up slightly (and then use an adjustable gas block).
No. Your upper runs like a Goddam machine. Smoothest action ive ever touched. So much so that its going to be my bump in the night gun as soon as I figure out how to swap handguards. So if you find out that port size from FN i’d greatly appreciate it.
Sweeeet. I drilled it out with a 5/64’s drill bit so that should be fairly close…was originally .062 if I understand the math on this correctly…yeah way undersized…
After reading this I need to check my PSA 10.5", my PSA 11.5" runs smooth on anything that I put through it but I really haven’t ran the 10.5" as much so I’m going to go out and try different loads!
I’ll run it hard with my class 3 lower because that 10.5" factory build runs smooth, but it is a Colt dealer sample I have had for years now.
