Mine is an over barrel suppressed job and it always groups very well except for once recently. It grouped about 3" so I gave it a clean and was back to tight groups again. I have always used Winchester 40 or 42gr subs. I have recently had a few 40gr subs sonic boom and a fair amount of bullet cases have a glue or similar substance on them which makes them hard to remove
Sent from my workbench
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