Same story , Have an AR that is haveing short stroke problems. EVERYTHING checks out. EVERYTHING. Swappped ammo ( quality stuff ) While it did function better with the Q3131A it still acted up.
 Its a Colt preban 1986 rifle. Less than 600 rnds through it. I have checked everything yall have  suggested. Im about to part swap this  rascal.  The ejection patern is great .It piles the brass up 6ft away  at a 5 oclock position if 12 noon was the muzzle . It has the style Bolt carrier with the UnHooded fireing pin. It normally don't jam but won't lock the bolt back and one or two rounds  pre 30rnd mag might not get back far anough to strip a round for the next shot. Rifle Colt A2HBAR 20" Factory rifle.
List of things I checked out :

Mags
Gas Rings
Gas carrier key staked and tight
Gas tube aglinment with carrier key
No binding in the buffer tube
Swapped to A good batch of Q3131A .No go .Ran better but not solved
No binding of carrier sliding in upper
Lubed properly, Breakfree,or FP 10, or Mil com.
I cleaned the gas tube with Gun Scrub by shooting it down the tube for 10 seconds.

Along time ago I did something stupid. I tried some reloads in her and she malfuction terrible. I threw the rounds away and put the rifle in back of the safe for many many years. Could the power residue from these shitty rounds , while sitting up so long cause this and hardened up to wear Gun scrubber and the blast of quality ammo going threw the gas tube not blow the it out and be acceptable. Guys Im reaching deep and about to go to a Palm reader on this one. Im not claiming to ever be an expert but I know AR's and this one has me mind boggled. Thanks for hearing me unload. Thanks to the Ga Gang for any replys I might get WarDawg.
 

You didn't say what you checked with the gas rings-are the gaps in the 3 rings all staggered well? If they are all lined up, or really close to being lined up-that would cause problems similar to what you are experiencing.

By any chance are you running an A1 length stock with an A2 rear butt stock screw. If so.....the longer A2 screw protrudes into the buffer tube and limits the distance the rifle length buffer travels and will cause short stroking by about 3/4".

McFarland one piece rings work fine but are no better than three seperates. The bigger key to the three seperate rings is tension. Misaligning the breaks has pretty much been proven doesn't matter. Gas ring tension is what is important.

What about your FSB/gas block? Have you removed it to look at the barrel port in relation to your gas block port? Misaligned maybe? Could be a piece of something from them handloads you ran obstructing the gas port. Again......just an idea to look into.  Look heavily at the gas system operation first to solve short stroking.

Quoted: You didn't say what you checked with the gas rings-are the gaps in the 3 rings all staggered well? If they are all lined up, or really close to being lined up-that would cause problems similar to what you are experiencing.

Thanks for the reply. Yes I made sure the rings was staggered.  While some say it doesn't matter, I know that is a trouble shooting procedure in my M16A1 rifle manuel I was issed in the military. Its sitting in front of me right now. Thank you for the reply, WarDawg

Quoted: By any chance are you running an A1 length stock with an A2 rear butt stock screw. If so.....the longer A2 screw protrudes into the buffer tube and limits the distance the rifle length buffer travels and will cause short stroking by about 3/4". McFarland one piece rings work fine but are no better than three seperates. The bigger key to the three seperate rings is tension. Misaligning the breaks has pretty much been proven doesn't matter. Gas ring tension is what is important. What about your FSB/gas block? Have you removed it to look at the barrel port in relation to your gas block port? Misaligned maybe? Could be a piece of something from them handloads you ran obstructing the gas port. Again......just an idea to look into.  Look heavily at the gas system operation first to solve short stroking.

It is a factory rifle thats never been altered. There could be an obstruction but the ejection pattern on my spent cases indicates it's getting plenty of gass.6ft ejection to the rear in a nice pile.If Im shooting in a fixed postion with little movement I can fire 30 rnds and nearly place a paper plate over the spent case pile and nealry all of them will be under the plate.   It does have the unhodded carrier and hammer with the knotch cut out in it from COLT. It does give alittle more resistance than a standard carrier with a full hood and non knotched hammer... What ya think ?? Im I reaching to far with that idea??? Thanks again WD