I did some measuring on using a 223 Rem barrel as the possible donor. The barrel measured 1.115" at 3.4" from the chamber end, just before the taper began and the sight holes were 0.175" deep, #6 screw. I guessed the best thing to do was to leave the sight screw holes full depth, and possibly increase to #8, then bore out to 0.940" less the major dia of whatever thread I decided to use, 0.940" being the difference between 1.115 chamber dia minus the sight hole depth.
If I used a standard size case, 0.473" dia, that would leave 0.234" walls, minus the thread major dia. That would mean walls about 0.406" thick, counting the 0.175"
I also though about using a .284 case at 0.500" and would lessen the wall thickness by about 0.014".
I measured the walls on my 45-70 at 0.306" thick so I could even go to the WSM case and still be safe...I think. I'm not an engineer so calculating what the case and pressure would do to a barreled receiver with a threaded portion almost right in the middle is not in my milieu, but I think it would work.
I also though about threading the full length of the stub, 3.4" or whatever it ends up, less a very short shank about 0.025" or so, with a shouldered barrel of 1.115" dia to match the stub. Once the barrel was headspaced and witness marked and a flat milled on the bottom wide enough for a wrench, it would be just like any old switch barrel rifle.
It looks promising. I always had a 375/284 in the back of my mind, or maybe a 416/284?
Maybe the same calibers on a WSM case? That would leave walls about the same thickness as the 45-70 chamber.
Any comments about the threaded portion handling 52,000 psi plus or minus?
Thanks NFG