That's an incorrect assumption. All you had to do is ask. I'm here for information, not an e-argument.
Who's arguing? We're giving you information, whether or not you like it, or want to hear it, isn't my problem. I personally couldn't care less if that shotgun works for you or not. The first dozen replies in this thread mentioned a problem with ammo. The only one being argumentative about your issue is you.
My buddy had some old assorted name brand ammo he wanted rid of, including brass. It performed Less Bad, for lack of a better term.
So you replaced one set of known bad ammo with another set of unknown ammo and it also performed poorly. Ok, I'll ask. Did you bother shooting it with GOOD AMMO? Not just different ammo, but good ammo, with a long standing positive reputation.
I'm not talking a little notchy, I'm talking it catches and you have to put the butt on your leg to get enough leverage to eject.
Does your mossberg have dual extractors? Mine does. But if the Mossberg tech is having difficulty identifying any issues with your shotgun, again, maybe it's not your shotgun that's the problem. They'll probably make it right, up to and including replacing the gun entirely.
His half-worn autoloader ate that stuff up too. We didn't pass any to the guy with the new 870 since he was running just fine on the mythical Winchester Jammomatic ammo.
Proves nothing. What were the lot numbers of the ammo you were shooting versus the identical ammo that wasn't giving the other guy problems? As ammo is assembled in lots, problematic ammo can be had in lots, which may vary widely in quality. It's luck of the draw, you may have purchased a bad lot, while the other guy had one just fine.
Mossberg's lead technician claims to have been on the case for the past three days. He still can't provide an answer what the problem is, much less the solution.
Which still leads me to believe that the issues lies not with the gun. Sounds like he can't tell you what the problem is because the problem hasn't been replicated. Those in the mechanical field call that operator error. I deal with it every single day. If the ammo is getting stuck in the chamber and you need to mortar it open, it very well could be a chamber problem. But a Mossberg tech would be able to check and identify that as the problem with the first hour, not take three weeks. They could be backlogged and understaffed and haven't gotten to it. The CS person may not know what the service and repair dept. is doing. Who knows? Give it time and have a little patience.
I still think you had a box of out of spec ammo. The older autoloader, being worn, probably has a looser chamber than a new in the box Mossberg built to better tolerances than a budget Remington 870 Express, which don't have the reputation for quality they used to have.