[Sneeky]

I’ve got a Mosaberg 500a I acquired used of unknown age and prior use. Was recently shooting it and after about 20 rounds in a short time (2-3 minutes) it jammed - could not open the bolt. After about 5 minutes of fiddling with it, it seems like it finally unlocked and I was able to rack it and then ran another 5 rounds through it without incident.

I haven’t looked at it since. Any ideas what might cause that, what I should look for?

 

[Jlrhiner]

Give it a real through deep cleaning. Then try it again.

 

[GunDog]

IPNI. Check make sure your ammo isn’t causing it. Not a whole lot to go wrong with a pump.

 

[dmas]

Sounds like short stroke to me.

 

[Steve_In_29]

OP had you lubed the gun before shooting it?

I don't think it's applicable to a Mossberg but I have had issues out of the box with the bolt not unlocking on my Win 1300 due to brass being too thick on the rim. This is due to the rotating bolt not having enough clearance. Winchester fixed it and sent it back and I have had no issues since.

 

[roseman]

If you were using reloads, it's possible that the brass needs to be resized before loading new rounds.

 

[Sneeky]

I was using relatively new, production Winchester ammo at the time. Before that had fed it Remington, Estate, and some reloads with no issues. Did not lube it recently. I was thinking maybe it was getting hot and seized, and when it cooled enough it un-seized. 🤔. I dunno - never had that happen to me before.

I’ll clean and lube and try another box of ammo through it on a hot day - see if it suffers reoccurrence.

 

[elliott264]

Winchester shells are notorious for causing jams. The aluminum is thin and expands too much. If the chamber isnt perfectly smooth, this can cause jamming.

 

[Steve_In_29]

You never had it happen before with "that" gun or did you mean with any other guns you had shot?

 

[Solidus365]

Likely the brand of ammo. My Remington 870 will jam up with some of the cheaper stuff. I'd also do a full disassembly and thoroughly clean, lube and inspect all parts for anything like a burr that could cause a hangup. At the end of the day, modern inexpensive pump actions are capable of malfunctions and some are prone to them.

 

[Steve_In_29]

Likely the brand of ammo. My Remington 870 will jam up with some of the cheaper stuff. I'd also do a full disassembly and thoroughly clean, lube and inspect all parts for anything like a burr that could cause a hangup. At the end of the day, modern inexpensive pump actions are capable of malfunctions and some are prone to them.

Rem Express?

Replace the extractor with one from a Wingmaster and polish the chamber.

 

[Solidus365]

Rem Express?

Replace the extractor with one from a Wingmaster and polish the chamber.

Yeah the express. It is quite reliable now that It's broken in. Honestly I'll probably just replace it with a Benelli at some point lol

 

[GunDog]

Mossberg is usually a reliable brand.

 

[Sneeky]

I only have 2 pumps but this is the only time I have had a pump jam and never saw any others jam ie friends using them.

 

[Bobcat In The Woods]

You might also want to lube your locking lugs and extractor assembly.

I’ve never had issues with any ammo in my 88z

 

[Iamfarticus]

Sounds like short stroke to me.

That's what SHE said....

 

[Forrest Mosby]

I have a 500 and a 590...also a Youth 870 20 ga..never a prob w any of them...Most likely issue is ammo followed by crud..jmo

 

[Bobcat In The Woods]

That's what SHE said....

When did you meet my girlfriend?

 

[fflincher]

I've had two problems with Mossberg 500 series shotguns.

One involved not having the nut on the end of the magazine tube screwed down far enough.

The other was more involved. The Mossberg trigger/hammer group is housed in plastic. After hard use, the
trigger/hammer group gets loose in the receiver. You can see it if your look for it, the greatest point of looseness is in front of the assembly where there is a plastic lip that should be held up firmly by the metal receiver. If the plastic is worn or otherwise damaged, the trigger/hammer assembly can drop down far enough to cause missfires. Best answer: new assembly.
DIY answer: cut a groove in front of the plastic assembly and force in a flat bar of steel that will bridge the space between both sides of the receiver and support the old assembly.

 

[roseman]

I keep spare trigger assys for the Mossbergs because they are plastic but I have not had to use any so far. That is the only plastic part on the older ones I own.