Mine is overbored at the factory (should still have chrome lining, then, I would think), with a diameter of .742. That appears, from this SAAMI sketch (2nd page) to fall within the boundaries of standard 12ga.:
http://www.saami.org/pubresources/cc...ge%202_3-4.pdf

That would seem to suggest I'm *safe* to shoot slugs, but I probably won't have as good accuracy.
Crazy what Mossberg did/does, making a .770 barrel! I learn something new everyday!

I'm pretty sure it will fit. The chamber is in the barrel not the receiver so you will basically be converting it to a 3 inch. Your bolt throw is just longer. Should be a non issue as long as the barrel will fit the receiver properly.

That is what I hoped to hear. Still, though, there is an ominous warning against it on the Winchester link you posted earlier that gives me pause: "IMPORTANT: Do not attempt the use of 3 1/2" chambered barrels with 3" receivers nor 3" chambers with 3 1/2" receivers." On the other hand, it could be that they're simply concerned about someone putting a 3.5" shell in a 3" barrel or a 3.5" shell being crammed into an action that's too short. It just wouldn't make sense for them to only make it possible for someone to shoot slugs if they had one of the two chamber offerings.

I'm not sure what their problem with it would be. Other than someone screwing up and using the wrong shell. Maybe the bolt travel length is an issue. But they are sure saying DO NOT DO IT and they dont offer a 3.5 length rifled barrel. Oh well. I'd say go with your better idea anyway and get yourself a nice muzzleloader! I just got back into them myself a couple years ago as I am tired of the dang recoil from my slugger. Plus, with my TC anyway, I have more range than I do with my 12 gauge slug barrel. Lots of MLers out there nowadays that, with the right load and bullet, can be easily effective out to 250-300 yards. My barrel prints under 2 inches at 200 and can often get dang near one hole 5 shot groups at 100.

I'll probably just call Winchester at some point just to be completely sure what the deal is. In all likelihood, all that'll get me is a conversation with someone who just reads back what's printed on the site, again---without being able to tell me why.
Either way, and if the slug barrel is an option, I have time to decide. I'll just hunt rifle this year, and next year I can decide if I want to dish out the extra money for a muzzleloader (and maybe a scope) or turn my shotgun into an all-around.

That's interesting.... The chamber is on the barrel, and you would think it would make no difference in that situation.... I'd call them, you're probably right, but it's worth a call at least maybe you'll figure something out.
-Jake

I can see why a 3.5" chambered barrel would be ill advised being put on a 3" receiver but there are many shotguns out there actually designed to accept 2 3/4- 3.5. If your receiver is set up for 3.5, I just can't wrap my head around why they so strongly state NOT to use a 3" barrel on it. Maybe Mercy will chime in here with some techie jargan that will most assuredly give me a headache

Perhaps you might PM him; if you think it'd be beneficial, then Lord send Mercy!

Already did, he shall grace us with his technological wizardry soon I imagine.

As I said earlier, the only thing I would imagine is they are worried some mental midget would try to stuff a 3.5 in that 3 inch chamber since the receiver will accept it.

Well fellas - as they say, a picture is worth a thousand words:

SXP Replacement barrel for 3.5" compatible receivers:


SXP Replacement barrel for 3" compatible receivers:


Looking at how each barrel type engages the receiver, it looks pretty clear the receivers, and the barrels, are different. Interesting to see that, and very odd, but it does indeed look like the receivers and their respective barrels are different.

Both pics stolen from cheaperthandirt.com's item pages, but if you dig around Winchesters site on this particular mission (ain't easy to find the pics), you'll find the same difference - specifically I found the pics with the same barrel tennons on these pages: the buck/bird combo model is a 3" model and shows a barrel tennon which matches the 3" barrel above, and the barrels page under products has a 3 1/2" barrel depicted at the top of the page which matches the 3 1/2" barrel above.