Winchester Model 50 12 GA jams on third round

[4V50 Gary]

Apparently the carrier lock swings out and prevents the third round from exiting the magazine. Any thoughts as to why?

 

[4V50 Gary]

Upon further examination, I think it's the missing carrier lock screw that allows the carrier lock to flop around too loosely.

 

[Dixie Gunsmithing]

I would think that would stop the carrier latch from operating correctly all the time, with each shot, but if it is missing the screw, it will most assuredly cause problems. The hulls rim makes contact with the latch each time, mashing it in, which releases the carrier to come up, and the bolt to come forward.

You might try placing a punch or pin, close to the screws correct diameter, in the screws place, and trying the gun to see if it works. Make sure it is long enough to easily pull out.