gunguy, you probably have burrs in the hole on the frame where the base pin latch goes. the burrs will prevent the latch from fully seating in that hole. the fix is to remove the burrs. if you want to tackle it, use a small round file and/or emory cloth. be careful, though. that area of the frame is difficult to get to without marring up the frame finish.
suggest you get the belt mountain pin, regardless. have em in all my ruger SAs. fwiw
murf