Just a word...fellow SR22 shooter was using his at one of our club's Ladies Day events using Thunderbolts supplied by the club..about 500 rounds he noticed bullet keyholing.
The problem was excessive leading..was a chore cleaning it back to as new condition..lot of elbow grease and wound up using a .243 brush. Said some of the lead came out in shreds/strips. He figures soft uncoated bullets and PERHAPS lightly graven lands and grooves were the underlying causes
No ill after effects and he's back to shooting copper-washed bullets including MiniMags.
I've had no issues with my SR22 shooting my usual stuff but think I'll avoid Thunderbolts..just because.
Best.