Details
Did you ever hear of the case of the self-ejecting firing pin?
1200/1300 etc. seldom have problems with the feed throat, but that can happen every once in a while.
Ejector locating tabs in some guns use a tiny screw to locate, and if loose or backed out: jam or lost screw is likely, bent or dragging ejector can occur.
Improper barrel assembly can wedge the ejector, if the front tail is not inserted in the left clearance slot (on RH guns) of the barrel extension. Bumping the ejector with the barrel off can dislodge the rear tail of the ejector being located by the tiny pin showing at the left rear outside of the frame. The spring behind the ejector may come out of it's hole, too.
Keep the bolt most of the way back to keep the ejector more compressed and likely to be harder to knock loose. Otherwise, the first sign of a problem is when your gun won't pump fully to the rear and feels like it has something in the way being pinched. There is, and by now you have bent the tail of your ejector.
Pump arms can break a tip off, but usually because the spot welds holding the arms to the tube have started to fail on one side, so the other arm has disproportionate load on the tip that ultimately fails. Both arms can lose the connection at the same time then, just in different locations.
Plastic trigger housings are more vulnerable to cracking, but not denting like metal. Don't lean that side towards the fireplace or wood stove, either.
Standard warning from me about crooked choke hole installations. I have cut off the ends of more than one barrel that have choke holes so far off center that the edge of the tube is exposed and vulnerable, and one that only has the burr at the edge of the hole (from another sloppy factory job) keeping the shot/wad from peeling the tube (yes, it is a Winchester, as is one of the others mentioned). I cut and re-thread properly many barrels for discerning shooters that prize accurate work (and shooting) more than saving a buck. Ammo that is wasted from shooting off, plus wounded game that is not cleanly dispatched, all should be part of the calculation of cost balance. This doesn't include the psychological benefit of hitting more consistently since your barrel shoots straighter.
How is that for a list?
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