I picked up a few old shotguns for parts guns. One of them is intact. The problem is you almost have to hammer the bolt in and out of the action. It is an old Mossberg. I cant see any obvious bulge. That said, how do I look for a minor bend or slight bulge in a very short length of the barrel? Then how do I straighten it? I figure it is worth a try and as it is already screwed up it can't hurt for me to try. The gun is fairly low end so isn't worth paying someone to fix it especially as there is no emotional tie to it.

Mike, A bent barrel will not have any effect on bolt movement. Sounds like something is interferring with the bolt. A common culprit is the bolt stop screw, located on the left side of the action. If you can remove the bolt from the action and the screw is seated, the nose of the screw is broken or worn and may have galled the bolt.

Thanks Mike I will have a look and get back to you. My gunsmith skills have always been limited to writing a check. That just isn't practical anymore for anything minor and especially not for a gun like this. I appreciate the help very much. Thanks again.

Sometimes the action itself can be slightly 'collapsed' for lack of a better word on these.
The action is nothing but a section of heavy tubing with cut outs for the parts to operate.

If the action is put into a vise and pressure place on it w/o something to suport it from the inside (like the bolt body), certain areas can bend inward very easily.

Thea area on the right side that forms the locking surface for the bolt handle is mearly a tab of metal sticking up unsupported as the slot is usually milled out on top for the bolt handle to pass by.
That can bend easily enough by being dropped on a hard surface.
The cut out for any magazine parts is a weak spot also.

Take a close look for the bolt binding against the side walls of the frame.

Do an eye-ball scan carefully down the sides looking at a good light source and see if you can't see a bend or two in there as well as an obstruction as Mike mentions above.
It takes very little to bind the bolt up on these.

Check the bolt itself. Makes sure the extractor is seated in it's recess correctly and isn't creating the problem. IIRC they are just a stamped out piece and snap into a groove over the bolt head. If they are sitting a bit high or kinked a little, it'll bind up the bolt travel.

Take the trigger & safety right out of the gun. That way they won't interfere with any bolt movement while you're working out that problem. They're in with just a cross pin for the trigger and a larger headed screw to secure the safety.

A small diameter coil spring is up inside the trigger itself,, so catch that from falling out when you disassemble.
Hardly any spring tension to deal with,,nothing to go flying accross the room!

Good luck with it. Good project to learn on.