guys i've got one of dennys 16''recon barrels and a m4 viltor upper with 10''larue ff when i tighten down barrel it turns and make feed ramps miss aleign ,bolt wont feed into ramp extions theres a little play between the barrel pin and the barrel notch in upper any help would be nice dont want too screw it up ??????????              ALL SET TORN DOWN and re assesambled all lines up the freekin gun noam s

Quoted: ... theres a little play between the barrel pin and the barrel notch ...

IMO, you should not have to mess with the upper, it should fit w/o any problems... something is out of spec if there is enough "play" to foul things up.

I have heard that taking a punch and hammer and peening in both sides of the receiver pin opening EVER SO SLIGHTLY and EVENLY will tighten things up some.  I have never had to do this though.