Hello folks, I'm new to the forum. I picked up a new Ruger MK III 22/45 and took it to the range for the first time last night. After about 150 rounds, it started key holing bad, and almost sort of back fired. At first, it would only key hole every so many shots, and I kept going (I should have stopped). Eventually, that's all it would do. I suppose I went through maybe 200 to 250 rounds in total. I tried to run a snake through it at the range, but couldn't get the brass weight of the snake down the barrel. Something was obviously wrong. Before the key holing, it was shooting OK for a new gun. I took it home and had a heck of a time trying to get a brush down the barrel. Took several tries and lots of CLP. Finally I did and out came a significant amount of lead. It was caked circumferential around the rifling right at the end of the chamber (at the start of the barrel). Once I got it out and cleaned the barrel, it looked new and shiny. I couldn't identify any problems with the feed ramp. I did notice there was some trouble feeding in the beginning. I was not using the best ammo, since the best ammo isn't available. I was using TulAmmo brass maxx and Aguila. I own 8 pistols and twice as many rifles, and I have never seen this happen before. Has this happened to anyone? I'm planning on contacting Ruger, and certainly switching to different ammo if I can get some. Pictures show a normal group, the key holing, and the lead pulled out of the barrel. Thanks a lot!