Was out shooting my New Model stainless .357 Blackhawk today. All I has was some Winchester .38 Spcl rounds, the cheap white box version. Every time I loaded it up, after 3-4 shots, I couldn't pull back the hammer to rotate the cylinder. Looked like the fired case heads were rubbing on the frame, just enough to cause binding - preventing the cylinder from rotating. Is this maybe due to the ammo or do I have some sort of problem that needs fixing?