My nearly new AR has suddenly started short stroking. It's so short that the empty brass never clears the barrel extension and gets rammed back onto the chamber.

Watching the carrier move shows that the bolt unlocks and starts to extract but never gets very far. The ammo is Lake City 2002 production, so it's not the ammo. Desides, it used to work with this stuff.

I will be talking to the builders of the beast on Tuesday in detail but I thought I would cast around here as well to get some ideas to add to the discussion. It's only had 600 rounds through it and it has been kept clean.

Everything in the lower looks and feels fine and the bolt is not binding in the carrier and the gas rings look fine.

This leaves a leak or a blockage in the gas system, either the port, the tube or the carrier key.

There is a carbon buildup on the front of the gas tube where it goes into the front sight tower but I'm not sure if it is normal or not.

The more I think about it the more I think it is either a bad gas tube leak or more likely I think the carrier key has got itself seriously blocked up so that most of the gas is wasted.

Any ideas how I can see if there is a blockage anywhere in the gas tube or the carrier key?

Slowworm.

Has the carrier key become unstaked and loose?

This can cause short-stroking.

BTW, some carbon fouling around front sight tower is completely normal.

Mike

The carrier key is staked and secure. I'm going to get some PVC tubing to put over the carrier key to blow through to see if it's blocked.

The problem is I don't know if the hole into the bolt carrier is supposed to be large (so should be easy to blow through and difficult if blocked) or small (or difficult to blow through or impossible if blocked).

I've only one AR so I can't compare.

Slowworm.

The hole in the top of the carrier that lines up with the hole in the carrier key is about an 1/8" diameter.

Is the roll pin in your gas tube?