This is my first post on the 308 forum, but I've been reading here for almost a year.
It all started with an innocent 80% AR15 project back in early 2020, which morphed into "needing more". One thing led to another, and one day I found myself machining an 80% AR308 DPMS lower. I knew then that I had a problem. At the time AR parts were pretty hard to find, prices were high, and I bought what I could find. The 308 went together pretty well, but I'm having failure to feed issues with my setup. Here's what I have:
CBC 18" barrel with mid-length gas. Gas port is 0.070"
CBC supplied BCG (make unknown)
5D Tactical 80% DPMS lower
Daytona Tactical DPMS upper (5D Tactical uppers weren't available at the time)
5.4 oz buffer, 5.25" long, and has a loose weight inside the buffer
308 buffer spring from ??
A2 buffer tube, 9.75" inside length
JP Enterprises adjustable gas block/FSB
Mid length gas tube that ends right in the middle of the bolt cam notch
Barrel nut tightened to 45 ft lbs
I'm firing American Marksman 147gr M80 ammo. Groupings are consistent at 100yds.
As far as I can tell everything is set up well. The gas tube ends where it's supposed to. The adjustable FSB is wide open, and the gas ports are lined up right. The gas tube is clean and clear. The bolt key engages the gas tube well. But the BCG barely moves after a round is fired. Once in a while it will start to eject the shell, but always hangs up in the chamber. I haven't once had a clean feed.
My gut tells me the gas port is too small. There is very little gas residue inside the upper or the bolt after 30 rounds. If the problem is the gas port, I have no idea how large to make it. I read the Forum article on Barrel Gas Port Size, but there is very little info on 18" mid-length barrels. What little there is makes me think my gas port is too small.
I appreciate any feedback you care to offer.