While I'm not "up" on the Model 1000, there were, as I recall two reasons for failure to operate.
One was a dirty gun and/or gas system and port.
The second was something about the gas system having some "O" rings that wore out and had to be replaced.
Gun Parts Corporation bought all the S&W Model 1000 parts, and after Mossberg sold the gun for two years and then discontinued it too, they also bought all of Mossberg's parts.
The gun should work with 2 3/4" shells or 3".
I just went all through this with mine.
What are the symptoms? Does it load the next round? Does it reset the hammer? (different problems/different symptoms)
The gun is very clean, and I am shooting light loads 2 3/4 shells. The hammer if I recall is reseting but the next shell is not ejecting. IS there a certain bbl needed to shoot slug rounds or will any barrel work? The gun is mostly used for skeet and trap and on occasion pheasent... so hopefully it doesnt need slug rounds to cycle.
The Smith and Wesson 1000 3" mag will not cycle correctly with standard 2 3/4 loads, much less light target loads. You can get away with very stout 2 2/4" mag type loads, but thats about it (read it's a 3" mag gun before the time that the mag shotguns could run both 2-3/4" and 3").
Looks like it time to stock up on some value cased lot shells in 3" mag for the shotgun.
any barrel should work with any load (barring choke considerations). Once you take off the fore-arm, the first thingy in the gas tube is the regulator, it should compensate for light/heavy loads.
Ok, let me get this straight-the first round shoots, the empty hull ejects, and the next (full) shell hangs up in the reciever?
If that's what you're looking at, i would examine the tube magazine spring. I had to get a new one 'cuz the one that came with it was all bolloxed up.
I love my 1000 and did a lot of work on it make it operate correctly.
I stand by to offer any help, in any way, i can.
I have been cogitating on your problem. I have been examining the mechanism and scratching my head.
It sounds like an extraction/ejection problem. I think you should start small.
With the bolt locked to the rear drop one shell in the chamber. Push the button to close the action. Fire.
Did the empty eject? Did the bolt lock back? Its kind of like adjusting the gas pressure on an FAL.
try the same process with some different loadings. Record the results.
This, I think, will give a good starting place for analysis.
(and please report back, I'm diing to know what's going on )