That's what i thought too. I did some looking around and that's what i found. Apparently, the hood is slightly larger on series 70's, smaller on series 80's. The feed ramp on the chamber sticks out just a hair more. Also there are a few minor differences in thickness of the lugs on bottom. I figured it was a shitty barrel.....but after having this problem 3 or 4 times... i did some investigating.