I have a Colt 16" that has a intermittent short stoke problem. This is a all Colt factory gun and has had several hundred rounds through it before it started this problem. When it does it it hits the case that is feeding up in the middle. It also seems like that it will do it more if you don't have a tight grip on the gun.
I've cleaned it, checked the aliment of the gas rings tried different mags and ammo.  the only thing that I can see is that at the bottom of the ramp on the bolt in the corner there is wear marks and a small bur. Could this have been caused by a bad mag hitting the B/C at one time? It almost looks like the hammer was hitting it at one point but the hammer doesn't have any wear marks on the edges.

Thanks

I was looking at the B/C and it looks different than my other B/C it is a factory Colt 16" but the B/C has a short ramp and the back part of the firing pin is exposed. When pulling back on the charging handle it feels like there is more resistance that with my other ARs that have the longer style ramp. Is this an older style B/C and the one with the more gradual ramp a newer style?   Should I just replace the B/C?