Gentlemen, certain aspects of this thread are trending into a discussion that ideally belongs elsewhere, and unfortunately most subscribers to this thread are not Premium Members and cannot get to that certain place, so let's stick to his question. (Much as i'd rather hear more about the other topic, needs must).
If you are experiencing pinky bite from the grip extension (and I am assuming this is a magazine buttplate replacement, not a slip-on grip extension), it is possible that the unit/s you have the wrong ergonomics for your hand, or your grip may need some examination.
Pics would be very helpful. Of the magazine extension I mean.