
Originally Posted by
demigod
I was running my Sabre 11.5" barreled SBR on Friday. (I haven't really tried to run it very hard yet) I started getting some short stroking.. Bolt overs, failure to lock back, etc. So Saturday I take out another lower to make sure that it's nothing to do with the buffer/spring combo in the host gun. Same problems! Great! I've narrowed it down to the upper.
But for the hell of it I pull the bolt group out of the SDI upper and drop it into a known functioning carbean. SHORT STROKE city.
So I have a Colt M16 bolt group that is giving me short strokes in two different guns? Bolts are staked on it. The one thing that I did notice is that there's a slight gap between the carrier and the key in front of the bolts.. in the area just behind the cam pin slot. I'm wondering if gas could be leaking there. ALL other parts on the group check out.
Robb? Grant?

I'd pull the carrier key. If it's leaking as I believe it is, then you'll see carbon tracking from the hole in the carrier usually going from the hole to the front edge of the carrier key. I'd replace the key with a BCM unit. If you don't have a BCM to replace it with you can reuse the key but hone/lap the finish off the bottom of the carrier key on an Arkansas stone knife sharpening stone (this insures the key is totally flat, not warped), degrease the key, screws and carrier. Reinstall using red loc-tite on the bottom of the key and torque to 55-60in lbs and stake it well. Let it dry for as least 12hrs, lube it up at the range and test fire.
Robb
Chief Armorer for Elite Shooting Sports in Manassas VA
Chief Armorer for Corp Arms (FFL 07-08/SOT 02)
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