Is the chamber clean? Is the expanded metal head on the shell hanging up in the chamber after firing? Have you tried different ammo? Are you shooting ammo with brass plated bases or with silver steel bases?

 

I’ll look more closely. Maybe I should put more effort into cleaning the barrel. That really is one place I wasn’t paying much attention to. It’s hard to say if the shells are hanging. I can’t see them until I cycle.

I’ve used a few rounds but I’m not thinking the ammo is the problem. It’s never had an issue before shooting these same rounds. I put a lot of steel rounds through it over the years.

 

Polish the chamber and see if it helps

 

I recently had some problems with an 870 I've owned since 1971, never the slightest problem with ANY ammo used previously 2 3/4"or 3". I found an online deal on 2 cases of Fiocchi target loads, the old pump would not function with them. I was totally puzzled but actually shooting warm up for a sporting clays pump gun event so I went to the clubhouse and bought a case of Federal ammo that I knew had functioned fine previously and completed the event without any more problems. Until a week ago, I never thought ammo could cause that in a pump, live and learn.

 

Yes, shells matter. I had a mossberg 500 as a kid that would jam with federal shells, all other shells worked perfectly. Check that before spending money on parts.

 

You might take a look at the extractor and spring.

 

Had a similar problem with 590a1. Polish/hone the chamber (I recommend polishing the whole barrel on all non-chrome lined shotguns). Check your extractor to make sure it's good. Check your extractor springs to make sure they're good. After all that, if it's still happening it's likely the ammo. My 590a1 will cycle every cheap junk ammo but not federal low brass...crazy. Even the best of shotguns can get a little picky about ammo, mysteries of life.

 

It is possible for certain shells to stick in a chamber. You could switch ammo, but the real fix is to polish the chamber. There is no excuse for a Mossberg to not extract a shell. Chamber polishing is common, and not hard to do. A cleaning rod that you can chuck in a hand drill make it very easy. I like use a bore brush, wrapped in fine steel wool, then a little lapping compount such as JB bore paste on that. Run the drill on high speed and slowly oscillate forward and back in the the chamber. I would estimate about a minute or two of polishing like that. Then pull the steel wool off, and replace with new steel wool. Don't use lapping compound this time, instead dip in bore cleaner and repeat in the chamber. Wipe the chamber with a rag and inspect. Repeat if you need, but one time usually gets them quite smooth.

Back to the original poster. There are a few reasons why this problem only started now. The first is you are using a different kind of ammo that isn't as forgiving. The second is your chamber is dirty. The third is you have a broken extractor. The fourth is your chamber got a little rust in it which can be hard to see. This is if I am understanding you correctly. You are saying that you are firing, pulling the slide back, and the empty shell is stuck in the chamber, correct?

 

Cheap Winchester shells?(super target/Universal)

 

Many years ago I loaned my friend a bolt action 22 to go squirrel hunting. When he returned it it was dripping water out of the barrel and the stock was like a sponge. He said he dropped it in the creek and handed it back to me like that. NEVER AGAIN will I loan a gun.😡