A friend of mine owns a Winchester 21 that occasionally "doubles" when he is shooting at a clay bird on the sporting clays course. He is trying to determine the root cause of the problem and what corrective measures might be involved in eliminating the doubling. I would appreciate your thoughts and helpful suggestions on this issue. Could this issue be eliminated by adjusting some screws etc. ? Or, is this issue indicative of a more serious problem with the mechanism of the shotgun?

I appreciate the time and effort you are taking to address this question. Thank you

Possibly wear, but far more likely to be dirt/gunk buildup inside the action. If you/he do not have the proper tools and/or do not know what you are doing take it to a qualified professional.

The distance between the trigger plate and top latch is important on a model 21, it’s controlled by a screw. It’s not unusual for gap to get out of wack. Its common to make a tube spacer to control this gap.

Has your friend asked a few others to shoot his gun, just to eliminate as many possible causes as possible?

Bama,

I have a 21 , not doubling, curious as to more info on this trigger plate and top latch relationship?

Many thanks to all of you for this helpful information. I appreciate your efforts. It's looks like the shotgun will be taking a trip to a gunsmith knowledgeable on Winchester 21's.

Good move. Too good a gun to risk a screw up.