What cartridge?? Are you shooting a light or a heavy for caliber bullet?? And what is the twist rate of the firearm??

I had a single shot NEF that was a 223. I could not get it to shoot-period. Then I had the throat measured, and it was unbelievably long. I think they made them to shoot the military heavies(just a guess).

By pop open do you mean automatic extraction of fired casings?? Or do you mean the action is hard to open?? I am not sure how a hot load would make the action hard to open?? I shoot some hot loads in my Encore's, but it does not affect the opening of the action, but it does affect the extraction. Tom.