Wednesday, December 18, 2013

Diagnose this Malfunction, Redux

Details- Gun is my AR Pistol.  Del-Ton lower, DPMS LPK.  Palmetto State Armory Pistol Buffer, Spring and Tube.  Upper was bought as a complete unit from a reliable source- 7.5"bbl, Spikes Tactical BCG. 

Ran fine for a long time.  Now, it has just mysteriously become a single shot.  In the videos above, you will see some times the casing is halfway extracted.  Those are times that the gun is not braced.  When it half extracts, it was braced against my chest. 

I have given it a good cleaning, ran the bolt both wet and dry.  The only thing I can think of is it somehow being undergassed.  But how does that happen just all-of-a-sudden?


  1. When was the last time you cleaned the gas tube? Also the keyway in the bolt where the gas is ported to the bolt and the bolt gas rings? Thinking more, check the gas rings, this reminds me of an issue I saw back in Basic in 85. a guy in my platoon, his rifle was a single shot and had to be run manually. The armorer said one of his gas rings had broken allowing too much gas to escape before the bolt and carrier could cycle. If they are not broken be sure they are not all lined up, you have to stagger the rings cuts. On my Franken-15 I space the cuts equally around the bolt.

    1. I have checked the gas rings, and they are not aligned, and the gas key is tight. I cleaned the bejebus out of the chamber last night in case there was some crud sticking the casings in there.

  2. A clamp on gas block can move forward an close off the gas port. This can be caused by misallignment of the gas tube to the key, check this by slowly allowing the gun into battery with your thumb lightly touching the bolt if you feel the gas key engage the key adjust the barrel nut to improve the alignment. Gas pressure could also move the gasblock forwardif it is improperly secured. The milspec front sight/gas block is the most reliable as it is pinned to the barrel, some aftermarket clamp on styles will move

  3. I'm guessing a loose/shifted gas block, assuming same ammo used. Pull your hand guard off and give it a look