I was shooting some factory loads out of my Ruger GP-100 today, and had one that locked up my cylinder. After many swear words and fighting with the cylinder, I finally got it open. I inspected the case, and found that the dimple usually left in the primer by the firing pin was pushed out backwards, and the primer was backing out. I am assuming this was caused by overcharging the case, or using the wrong primer. Anybody else have any problems with Remington's UMC ammo? I stopped using these rounds as soon as this happened, so I am not sure if any more in the box had problems.