A friend of mine gave me a complete set of parts for an Ithaca 37, minus the receiver. I have a receiver, and I placed the parts into the receiver.
I put it together, and placed a couple of dummy rounds in the magazine tube, worked the action, and the round would not feed into the action. With the action open, I depressed the shell stop with my finger, and the round cycled into the action. I fired, pumped the action, the fired round ejects, but a new round will not feed into the action. The new round will not feed, because the shell stop is not being depressed.
I am not sure what depresses the shell stop, but it appears that when the action is open, the shell carrier is supposed to depress the shell stop. If I push a little on the carrier when the action is open, it depresses the shell stop. It seems like if I widen the carrier a little, it might catch the shell stop.
So what do I have to fix or replace? Should I try bending the carrier a little wider, or perhaps replace it?
Should I replace the shell stop?
Should I replace the shell stop spring?
Or could it be something else all together?
Thanks for any help or comments.

Be sure the 2 screws that the carrier pivots on are seated in the holes in the carrier. It is possible to only have 1 in the hole and the other pressing against the side of the carrier, bending it enough to miss the shell stop. May not be your problem, but is something simple to check. It may also be the carrier was slightly bent when you got it. Either way, a LITTLE bending should fix things.

My late father's M37 (1950 vintage) developed a feeding/jamming problem. I replaced the magazine tube spring and solved the problem.