Interesting you are going to attempt this, Ahmed577. When I saw my buddy Brad's tightly choked .410 SxS, I asked him if he'd let me choke them, or one or just the tubes.
I figured the right barrel, rifled just the choke for a 3" hull and perhaps a 220gr. cast projectiles, would be a cool deer rifle. I haven't tried it, but I thought the case should hold about 80 to 90gr. of powder. A fired 2 1/2" WW case is just over 2 1/2" long and holds 65gr. 3F level to the top. Perhaps 80g.r is about maximum. Still, a decent load, but the bullet would have to be sticking out, some.
He did not want to do this, so the project was scrapped, without any more consideration. This type of work is likely beyond me now.
A rifled barrel used as a guide would have been used, in my case, to do this "work". I also no longer have a long enough bench. LOL - Just thought of that.