[firestar]

A friend of mine bought a old Moss 500 2 3/4" 12 ga, he then bought a 3" chambered barrel. Is it now a 3" 12 ga or is the reciever not strong enough to handel it? Would there be a safty concern with shooting 3" shells out of it?

[stevelyn]

The receiver is plenty strong, but it's not an issue since the pressure of firing is contained in the chamber via the lock up between the bolt and the barrel extension. That's what the little square cutout in the barrel extension is for. When the bolt closes, a locking lug fitted inside the bolt body cams up into position and locks the bolt to barrel extension containing the pressures on firing and can only unlock when you cycle the action.
The Mossy's receiver is aluminum and couldn't contain firing pressures anyway.
The problem you are most likely to have is a failure to eject the fired shell which will hang up at the chamber mouth. Although unfired 3" shells might cycle through without hanging up. Guns designed for 3" shells have a longer ejection port and longer bolt travel to ensure clearance and reliable ejection for the longer shell. Additionally there may be feeding problems due to a shorter feed mechanism.
If the gun originally came as a 2 3/4, I would keep it as such. You can still accomplish anything that needs done with a shotgun using 2 3/4" shells.

[firestar]

Thanks. I don't think he needs to shoot 3" shells for any reason but it is good to know he can if he wants to and the worst thing that will happen is a jam. Who knows, maybe he will get a bunch of it for free and he will want to shoot it up or something.

[Dave McCracken]

Free 3" ammo isn't common. I suggest sticking to 2 3/4" stuff in 2 3/4 guns, even with a 3" chamber. Some jams are easy to unstick, some are not.