On the one that's not grouping for you...check the muzzle with a glass and see if there are any nicks in it. Also make sure that the chamber is locking up straight with the ramp on the throat. If all of that is fine then I would shoot a few balls through it with lapping compound on it just to smooth up the lans and grooves. Load the ball and then place a little compound over the ball. it don't take much and can make a big difference.
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