In these times of ammo shortages we are all using and buying whatever we can find. Notwithstanding this, I have decided not to shoot Thunderbolt .22LR in any of my firearms anymore. On one occasion my Mark III was so clogged in the chamber from firing T-Bolts (about 100 of them) that it would not load rounds reliably. On another occasion recently one of my Mark IIIs suddenly started shooting highly erratic groups and completely lost zero. Turned out that the barrel was so heavily leaded from shooting 150 T-Bolts that the rifling was completely defeated. I have NEVER experienced anything like the above with any other .22 round, or any round. Even cheap Centurion .22LR is wildly cleaner and better than T-Bolt. I read some of the threads about T-Bolts but attributed it to just Internet complaining like you sometimes hear. Not so. I experienced this in the past ten days, personally -- this is not hearsay. This stuff is bad news and I am not even going to use the rest of my brick.