By short stoking, I mean it's f*cking short stroking. Pre-ban green label lower. All the rest is Colt and nearly new. Several hundred rounds fired since rebuild. Everything is clean and lubed. Shooting 55 gr. Winchester ammo. It short strokes even without a mag. The same ammo works fine in my Galil and gets thrown 30 feet. My key is factory staked and tight. I've never fired lacquered ammo. Gas rings look good and fit tight. I hate these dependability issues. Makes me with the U.S. would have picked a different rifle.

Time for a good cleaning.

Start of with the barrel and do a good scrubbing. The chamber just before the last cut is always the place that guys miss.

The gas tube should be sprayed with clp and allowed to sit(spray from carrier end with the muzzle pointing down).  The CLP will clean the gas port to tube fouling.

The buffer and tube.
Pull the buffer and check the spring for binding.  Some times the spring end can expand(where it sits on the buffer). Also, if you don't clean here, then you may have built up fouling that is binding the works.

Hope this helps.

chgreen, What was replaced at the "rebuild"? If cleaning it from top to bottom did not fix it, you are now entering the realm of serious debugging. There are many sources - Time to use the search engine. Find "search"  and click there. Make sure that, each time, that you are searching the last 6 months, and use "short cycle", "short recoil", and "short stroke" as key words. You will get a bunch of threads with a bunch of advice.

Well, I just checked and I could not find the search engine... If you find it, it will be helpful.

ANyway, my two cents, check the carrier key screws for tightness, the gas tube for wear, the chamber for roughness or debris, and the buffer and spring for smooth movement. Fix any problems. If the barrel is new, polish the chamber. If the gas tube was not replaced, doing so is cheap and probably should have been done anyway. Possibly the front sight housing/manifold is not lined up with the port in the barrel - slide it off and look for tell tale signs.

Check it out and get back to us.

chgreen, look around on this forum. I just placed a lengthy list of things to check on a short stroke (Short recoil) problem thread. Stay with us and we will get it running.

Thanks for your help guys. I haven't found any evidence as to why it suddenly started short stroking. I'll take it out this weekend and try again.

Mine did that, replacing the gas rings was my fix. actually I used the McFarland continuous ring.