One of my trainees had a FTF right after a cleaning and re-assembly session. The bolt carrier is stuck cold. I can't budge it even with a dowel down the barrel. I've never experienced this before, any chance he installed the firing pin incorrectly? Could it be the bolt cam pin locked against the inside of the receiver?

Any experience with this kind of thing? Best plan of attack?

"FTF", Failure to fire, or failure to feed?

Is there a live round in the chamber?

Firing pin retaining pin, sounds reasonable, cam pin too, hard to say till ya get it apart.

[s]Best[/s] A plan of attack, (assuming bolt carrier is hung up in buffer tube, precluding normal dis-assembly) remove stock from rifle, remove buffer tube from lower receiver, at which point hopefully you'll be able to snatch bc/b assembly out rearward, without tearing up buffer retaining pin and spring too badly. Or whang bc/b in enough to separate lower from upper.

All I can think of....
Mike

Note: made assumption this is failure to "feed" based on your user name and that if ya could separate lower from upper ya'd know how to get things apart.

Correct. I know what I'm doing - just haven't done this before. I'm hoping to get some feedback from someone who has. We're in a training cycle right now, so I won't get to work on this rifle for a week or so. By then, the voice of experience will have spoken.

First look at what happened. A chain of events as it were.

After a disassembly and cleaning individual cycled the action. Carrier returned to battery and will no longer retract. Is this assumed correct?

Assuming this, you need to verify if you can hear the FP rattling around in the upper. If not then its doubtfull its the cam pin digging in the upper. Even without the FP retainer, the FP will keep the cam pin from rotating providing its still in the clearence hole of the cam pin.

Could it be the FP retainer digging in the side of the upper? You bet but it should have dragged at the start of the action cycling to begin with. In other words the carrier shouldnt have slammed closed.

A couple of things could have caused this action failure.

One is there could be cleaning gunk or a patch wedged in the bolt face/locking lug area. If it were up to me to trouble shoot first thing I'd do is pry the carrier to the rear. Take care not to damage the front lip of the ejection port well.

Take a narrow, but stout, screw driver insert it thru the ejection port and slide it in on the face of the front of the carrier. Right where you see it as you look thru the port.

Use the front of the ejection port as the fulcrum of your prying leverage. The carrier should move to the rear. Disengaging from the locking lugs and allowing free movement of the carrier assembly.

I have has this problem before and the fix was getting the crud or clearance blockage out of the engaging surfaces.

I am assuming this is not a range failure right? So a live round is not an issue? Also this is done best if you can seperate the upper from the lower.