I have a 16" Hbar that about every 3rd to 5th shot the carrier will hold open, but not by the bolt catch. It is sticking in the receiver extention (aka buffer tube). I have tried a different tube, but it sticks just as it did before. Just to be sure, I have tried different mag and ammo brands. I have had it hang a few times while pulling the carrier back with the charge handle too when it was new. I doubt I have 100 round though the gun and it seems a little better than it was during the first firing session. I plan to shoot the upper on another lower and the lower on another upper to see if which part is causeing the problem, but it will be a bit before I can get to the range, so I thought I would ask here to see what you guys think.