when the bolt mooves forward  some times it looks like the notch in the upper face of the hammer catches the lip of the firing pin and holds the bolt open ! What is this notch for and can I smooth it out to stop this ? Thanks Keith

Colt started this crap way back when they first brought out the AR15.  They cut away the underside of the bolt carrier to expose trhe rear of the firing pin and put that notch in the hammer, specifically to keep people from removing the disconnector to attempt full auto fire.  The idea was, and is, that if you pull the disconnector, the notch in the hammer will catch the collar at the back of the firing pin and, as you hsve already discovered, it will hang the whols assy part way open.

This technique is NOT part of any frderal regs about what a legal AR needs, and serves a very bad purpose.  Cutting away all that material under the bolt carrier lightens ir up, and causes the whole assembly to operate faster than the AR/M16 was designed for, meaning more stress and strain on the mechanism.

I have, for about 25 years, fitted my ARs with M16 carriers, rhat do not have that cut away place, cutting the rear ring back just far enough so that it can't trip an auto sear.  I've also installed M16 hammers with the little hook at the rear, that catches the auto sear, cut off.

Fortunately, the days of the cutaway carriers seems to be over.  Have seen comments on this site recently that Colt seems to have quit the cutaway carrier, and I just bought a DPMS lower assy the other week that had an unnotched hammer; which tells me that they too have quit the cutaway carrier number.  Recall also seeing a note that Rock River has stopped the cutawy carrier/notched hammer number also.

If your rifle is doing this it is because your fire control componants are worn out and letting the hammer slip. You need to replace or re-tension the disconnector spring, the disconnector, or the hammer. Depending upon where the wear is.

i just bought a new bolt carrier assembly and it had the firing pin with the larger collar, and it also hung up the bolt. i replaced it with an ar15 firing pin, and all is well. this was with a new bm lower.

I just took the leading edge off the notch in the hammer and it stoped doing it will this couse ant other troubles for doing this ? The bolt and every thing seams to be ok now. thanks for the info !!    Keith