45-70 "Choke tube barrels"

[rockstar.esq]

So I've heard references to a conversion kit for side by shotguns that allow a 12g to be converted into a 45-70. In particular I've seen some 30-30 barrels that are threaded at the muzzle so that they can fit like a barrel liner in a 12g coach gun. I realize that this won't make an African double nor will it be regulated so both barrels group perfectly. However I personally find a great deal of utility in the idea and I'd be thrilled to know about some resources where a person could obtain them. Thanks in advance!

 

[Jack2427]

I bought an early Russian made coach gun about 8 years ago, and the shop had 2 of those 45/70 conversion tubes fitted to the gun, so I got them also. If it would shoot straight it would be a nice "African" gun. But the accuracy with the tubes installed is somewhat worse than throwing rocks, actually using slugs out of both barrels gives a much better grouping that the rifle inserts. The groups? 12-16" at 30 yards! Past 50 you cannot get on the paper no matter what, with either barrel.

 

[brasskeeper]

somewhat worse than throwing rocks

I don't know, I'm pretty bad at throwing rocks