I have a Ruger 10/22 with a 20" bull barrell. This is a rifle I have put together from after market parts and only the trigger group, magazine and bolt with Volquartsen extractor and firing pin are Ruger. I have had this rifle only a short period of time. My Problem is my Armscor .22LR ammo is, with some regularity, blowing out the back of the cartridge case into the action and blows out the magazine. I am also getting approximately a 3 round burst instead of a single shot. Most of the time the rifle works properly and with very accurate shooting to 100 yards. I am wondering if the problem is with my bull barrel not having a big enough chamber for the cartridge causing it not to fully enter the chamber on occasion and the bolt hitting the primer setting off the cartridge with it partially out of the chamber? This might explain the multiple round burst. The rifle was completely cleaned before usage.