Quoted: you sure the catch is hooking the front of the bolt and not the front of the bolt carrier?
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Going along with what Tweak said, when I put a 9mm buffer in my Bushmaster carbine I found (after 15 minutes of trouble-shooting) the buffer spring was binding up on the 9mm buffer's body and not allowing the buffer to go all the way to the rear. I was seeing the same problem you are seeing. If I pulled on the CH *REALLY* hard, I could sometimes get it to go all the way back and the bolt catch would catch on the front of the bolt itself, otherwise, it was just barely catching on the bolt carrier.
Pull the buffer and spring out, and see if it's binding up on the buffer. If so, hold the spring in your hands and give it a twist to expand the spring a little bit... I did this and the buffer from that point on worked fine, so that it would catch correctly on the bolt catch on the last round.
Good luck.