new 300 blk upper; failure to eject, failure to feed
Posted: Sat May 26, 2012 10:35 pm
Seems I'm not allowed to post pics or at least can't figure it out. Unless someone would like to school me. In any event, no gun porn.
Specs:
SAA 300 blk 16" stainless h-bar barrel, carbine length gas
Aero Precision ar15 upper receiver
YHM railed gas block
DPMS ejection port cover kit
DPMS delta ring kit
Colt sp-1 lower with factory h-buffer
Colt factory bcg and bolt
Colt factory charging handle
Assembled upper Monday. Tested. Found bolt would not lock back after firing a single round from 30 round pmag. Also no ejection. PNW 155gr match and PNW 125gr ballistic tip ammo. Both supersonic. Removing gas block revealed misalignment of gas block and gas port. Maybe this block was meant for a free float handgaurd not delta ring style hand guard. Anyway, gas block port and was well forward of barrel port causing about half of barrel port to be covered and ineffectual. Ported gas block to allow full access between ports (kind of like porting cylinder heads). Testing shows barrel gas port perfectly centered in gas block port now.
Testing showed continued failure to feed and erratic failure to eject. Failed more often than not.
Found gas port in barrel measured .093-.094. Internet forum research regarding similar issues specified Midway's ARStoner barrel gas port at .104. Misaligned gas port explained original issues but upper still seemed undergassed. And research supported larger gas port needed at barrel. Opened gas port to .107 on drill press. Very carefully. Pretty scary drilling a hole in a $200 barrel.
Soaked bolt in CLP (run it wet). Sometimes still fails to lock back on empty mag. Feeds and ejects perfectly every time.
Mags are pretty new. Feed and lock back 223 rounds flawlessly. Bolt functions perfectly in sp-1 upper. Colt sp-1 rifle was purchased new in February and zero failures thus far, so interchanged parts should be gtg.
All indications are upper is still slightly undergassed. Concerned about opening barrel port anymore and necessitating an adjustable gas block to regulate an overgassed upper. I'm presently only concerned with running supersonic ammo for hunting purposes, although may someday ATF up and get a suppressor for subs.
Any advice?
Specs:
SAA 300 blk 16" stainless h-bar barrel, carbine length gas
Aero Precision ar15 upper receiver
YHM railed gas block
DPMS ejection port cover kit
DPMS delta ring kit
Colt sp-1 lower with factory h-buffer
Colt factory bcg and bolt
Colt factory charging handle
Assembled upper Monday. Tested. Found bolt would not lock back after firing a single round from 30 round pmag. Also no ejection. PNW 155gr match and PNW 125gr ballistic tip ammo. Both supersonic. Removing gas block revealed misalignment of gas block and gas port. Maybe this block was meant for a free float handgaurd not delta ring style hand guard. Anyway, gas block port and was well forward of barrel port causing about half of barrel port to be covered and ineffectual. Ported gas block to allow full access between ports (kind of like porting cylinder heads). Testing shows barrel gas port perfectly centered in gas block port now.
Testing showed continued failure to feed and erratic failure to eject. Failed more often than not.
Found gas port in barrel measured .093-.094. Internet forum research regarding similar issues specified Midway's ARStoner barrel gas port at .104. Misaligned gas port explained original issues but upper still seemed undergassed. And research supported larger gas port needed at barrel. Opened gas port to .107 on drill press. Very carefully. Pretty scary drilling a hole in a $200 barrel.
Soaked bolt in CLP (run it wet). Sometimes still fails to lock back on empty mag. Feeds and ejects perfectly every time.
Mags are pretty new. Feed and lock back 223 rounds flawlessly. Bolt functions perfectly in sp-1 upper. Colt sp-1 rifle was purchased new in February and zero failures thus far, so interchanged parts should be gtg.
All indications are upper is still slightly undergassed. Concerned about opening barrel port anymore and necessitating an adjustable gas block to regulate an overgassed upper. I'm presently only concerned with running supersonic ammo for hunting purposes, although may someday ATF up and get a suppressor for subs.
Any advice?