A while back...
I bought a used 870 express 12 gauge to slug hunt deer and sighted it in and never went slug hunting or really shot it. It seemed to work fine then.

Then one of the deer shack kids wanted a shotgun and I gave him a good deal.

Last weekend we were cow-pasture trap shooting and the thing wouldn't eject consistently without having to push the forearm forward to unlock or pump down really hard.

I told him to watch youtube to disassemble it and really clean it up and see me if there are issues after that.

So what may be wrong?
Cost to fix?

I'm going to pickup the bill on this for the kid...

Try this. Lots of good info on here. You may have to do some searching.

http://rem870.com/forum/index.php

Sounds like metal base ammo is sticking in the chamber. Is the chamber rough?

In other words, it's an "extraction" problem - not ejection..

Dirty/rough chamber.. Clean the snot out of it and try again..

Also - what shells? Factory? Reloads? Steel-rimmed? (those I'd stay away from, FWIW)

I will have him look. It was a used waterfowl gun so it may have seen a wet chamber.

It was every other shell and this kid is big and could put lots of force on the pump to the point I thought he would break something

Stuck spent spent hulls are pretty common with the crap steel these days.

OP Here:

It was a extraction problem. Sorry for the confusion.

Him and his brother were shooting brand new Winchester target loads. The other boy was shooting a mossberg and it wasn't having any issues.

I've had sticky winchesters before, but usually after they have been stored for a while and get corrosion on the ZNC coated rims.

I'll pass on your guidance.

Im still open to suggestions if this doesn't stop there.

Not clear on what you are describing when you say push the forearm forward to unlock on a Remington. Winchester has a locking feature on their older pumps that required a forward impulse to unlock the slide but that was usually initiated by recoil . The Remington however does not do this.

If you are having trouble unlocking the action after a shot the problem is probably due to a dirty trigger assembly. Notice if once the trigger is pulled if the little release lever next to the trigger retracts slightly if not I might suggest that you drop the trigger unit and soak it in mineral spirits drain it and then lube it with something like Remington dry lube.

If that's not the issue are you saying the fired hull does not extract easily from the chamber or it extracts but doesn't flip/ eject out the port . Extraction can be a dirty / rough chmber, swollen shells or a combination of both. A lot of shells have poorly formed rims that allow the extractor hook to jump the rim or the rim doesn't hit the little ejector bump on the inside of the barrel extension. So try the following

1 Take a toothbrush and some solvent and brush around the extractor recess in the both and make sure the extractor hook is moving slightly under spring tension. Also make use the hook isn't cracked or misshapen or to the spring is broken and thus the extractor is sort of loose in the slot.

2 Look feel on the inside of the barrel extension for the little bump that the rim hits to kick it out if it gone there is your problem. You will need to stake a new one on ( unlikely)

3 take a brush and solvent and clean the chamber area really well.

4 try different shells.

I bet you will find it is one of the items above.

Express models are re know for having rough chambers.

OP here...

Chamber polishing - can you get by with wrapping a little extra fine emery cloth on your finger to do the job?
dowel rod?
empty shotshell?

"Can" you do that? yeah, but it'll take you forever..

Take a (say) 1 foot section of 1/2" dowel.. Use a coping saw (or similar) to create a slot in one end, about 3/4" deep. Place a strip of 240 grit or finer into the slot and long enough to wrap around and get to a point where entry into the chamber is a bit 'tight'..

Chuck the other end of that dowel into a 1/2" drill and begin to polish the chamber.. Do NOT go inside far enough to get to the forcing cone - just the chamber itself..

Whole thing should take about 10-15 minutes and you'll have a nice, shiny chamber that should cure your extraction issue..

Best wishes.

I've had pretty good luck with wrapping fine steel wool around a brass brush and using semi chrome polish. Chuck a piece of cleaning rod into your drill attach the brush and polish slowly checking often.

OP again:

So what is your functional gauge?
A spent shotgun shell slip-fit?

Borrow a bore gage from the machinist at work???

I think it would be easy to over do it.

That's the reason I use the less abrasive steel wool and semi chrome polish and admonish to check often you want to polish. Not bore it out.

What Redneck said. Have done it but no 1/2 inch drill so I use a 3/8 dowel and 320 wet-or-dry. Also I don't worry so much about the fit, when you spin it up it acts like a flap wheel.

The idea is to knock off gunk and surface rust proud of the metal, not grind out pits. You'd have to work at it to hurt the chamber.

Gauge? Just go at it until the chamber looks shiny, doesn't take long at all, and go out and shoot it to see if it extracts smoothly now.