I can offer my experience. A good friend of mine brought me an "old German rifle" 5-6 years ago to inspect and help him get shooting. He knows next to nothing about small arms, but was one heck of an artillery officer. Anyway, his father brought it back from WWII, it is a System Adyt Schuetzen single shot rifle in your caliber. I chamber casted it with cerrosafe to verify exactly what caliber it was and the bore/groove dimensions. There was no "standard" for 8.15x46r back around the 1900s, bores could be 0.312" to -.326" approximately depending on gunsmith. His measured on lower side at 0.316". Finding brass was the hard part. I ordered a box of 20 loaded rounds from either Graf and Sons or Buffalo Arms (cannot remember which). One of those also had RWS fresh brass, I ordered three boxes of 20 which was NOT cheap. I remember it took a while to get in stock. I found a bag of 500 cast projectiles on GunBroker for ~$75 shipped. They were 175 grain, proper heel seated design. I see they have some 180 grain bullets in stock at Buffalo Arms right now. I bought Hornady dies off either Ebay or GunBroker, cannot remember.
I have read that you can make brass from 30-30 with some effort, requires inside rim turned down as they are too thick for 8.15x46r. You may have issues with rim diameter still in your bolt actions, I vaguely recall reading they are smaller in diameter also but could be mistaken.
I still haven't found a good load for it yet, but only tried one time. A modern smokeless powder charge is so small compared to case volume that my velocities were anemic and wildly varying. I need to get some cream of wheat or dacron case filler to keep powder against primer and try again.
All of this is way too much for my friend to tackle, the rifle and all the gear sites in a plastic box in the corner of my closet for the past 5 years. I need to play with it just so I can be done with the whole hot mess.