I bought my son a new 22/45 for Xmas. He shoots in a pistol association so I gave it to him early. We went to the range several times and put about 500 rounds thru it with no problems. Last week he shot in the competition and was shooting the Remington thunderbolt 22lr ammo. after about 30 rounds he started missing targets which is unlike him so we took the gun out to the outdoor range and shot a paper target. The bullets were keyholing. Upon inspection of the barrel we could see something in the barrel. It was lead. We knocked the lead out inspected the barrel and it still didn't look right. The lead was a ring around the inside of the barrel you could still see through the barrel. We thought it was a problem with the new gun maybe the barrel was defective. I called Ruger and they gave me a return # and said they would take care of it. I let my son shoot my mark one this week and he put about 25 rounds through it and started missing targets again Upon inspecton of the barrel guess what same problem. Well I hadn't sent his gun back yet so we decided to clean the barrel on his and mine and see if it solved the problems we were having. We shot the guns with different ammo and the problems were solved no repairs necessary. Just for kicks we shot a few of the remingtons through a 10/22 to see if it had any problems with them. The Remingtons started to lead it up also. I can't believe the 22/45 didn't suffer any damage there was quite a build up of lead in it but it shoots great now. Stay away from the Thunderbolt ammo it's Junk.