Original M16A1 with Geissele 2 stage trigger installed and all was fine until past weekend (also using VLTOR heavy buffer and spring, might be SOCOM version).  So I charge the gun with the selector in full auto mode and the trigger will not release the hammer (auto sear appears stuck on the very edge of the hammer catch).  Gun shoots fine in semi auto mode.  If you have the gun charged in semi mode and then switch selector to full auto, it will fire full auto just fine (sear is not sitting on the hammer catch). I am suspicious my sear or selector switch are not 100%.  I do see some dirt which I gave a once over as quick test.  I also observe some movement in the auto sear pin in both sides of the lower receiver holes (maybe in .0015 range but it is visible).  Thoughts?  Replace both parts?  What is tolerance range for auto sear holes?

Update: further cleaned selector switch and auto sear and now gun will drop hammer if charged in full auto selector position. Gun needs thoroughly cleaned...  Still do not like the play in the auto sear pin.

The only Geissele full auto trigger is the SSF, the G2S is not a full auto trigger.

It sounds like your timing is very late. The hook on the hammer has too much engagement with the autosear. The autosear should release the hammer when the front of the bolt carrier is between 0.08" and 0.12" from the barrel extension (0.1" is ideal). Assuming the autosear and hole locations are in specifications, I would very slowly shorten the autosear hook on the hammer, until timing was within specifications. You probably want to check with Geissele to see what they recommend, or if they offer a timing adjustment service.

The SSF is a two stage trigger ( in semi ).

Thanks KarlSG1. First I am going to thoroughly clean fire control area.  Then I will check out your dimensions plus address the observed play in the pin holes for auto sear (very small in .0015 range but visually real and sure to grow with more pin movement).  i am gathering class III names of the best aluminum artists for this repair.  M60Joe?  Others?

M60 Joe repaired the auto sear pin holes in my Oly/Frankford Arsenal RR.  It hasn't missed a beat with a decent magazine since then.  I highly recommend his work.

@gmccart3
Any luck getting it to run?

I have two factory Colt M16s. Both have a little bit of play in the autosear pin/hole. I agree, it’s a little disconcerting, though I’ve never had it cause an issue in thousands and thousands of rounds.

A factory Colt M16 should not need its autosear axis pin hole re-worked. Buy some pin gages and check the diameter of your autosear axis pin hole, I would bet it’s in spec.

You could use a KNS non-rotating autosear pin. That should stop the play.