About 2 years ago I had a idea to build a 410 pump action with a fully rifled barrel for deer hunting here in Ohio, We cannot use any cartridge rifles here but a 410 is legal.
I own a Remington 870 Express in 410 and a Mossberg 500 in 410, after looking at there bolt lockup into the barrel lug I decided that the Mossberg would be the eaiser of the 2 to rebarrel.
I started with a 44 cal. barrel blank and turned it to fit the receiver very closely and milled off the tang extension and hand filed the hole that the bolts 1 locking lug fits into. I chambered it with a straight reamer that was big enough to allow a 410 casing with a .430 bullet inserted to chamber about .484 dia.
The attachment lug that has a screw thru it into the magazine tube I built and was silver soldered onto the barrel. The gun is now scoped and will put 3 Hornady 240 gr. XTP's in a 1 1/4" group at 100 yards, sometime even smaller.
I am shooting these out of new 2 1/2" 410 casings with jacketed 44 cal. bullets in the area of 1200 FPS. I tried different cast bullets and they shot OK but were less accurate, I also can safefully get at least another 300 FPS out of this combo but when I found this sweet shooting load I said Ill leave it at that because it will certainly kill any deer in 100 yards and has very low recoil .
Now the Rem. 870 is a better gun, but as Graybeard said the design of the bolts lockup is not strong enough for a 45-70 that has a warmer than trapdoor load in it. It could be built on a similar gun to the 870 but like others have said it would not have a large enough appeal to make it profitable.
The gun that I built could very easily be made to shoot 444 Marlin but I like the idea of staying with the plastic cased 410's as they will let you know how much pressure they will tollerate and that keeps you from hot rodding it, a 444 on this shotgun action would get you into trouble.
Jed