I just acquired in Eddystone rifle that is been through some very careful customizing and was in an estate auction until recently. It has a 30 inch very heavy barrel, it still has the factory trigger but it has been very carefully smooth out and tuned and is almost as good as some high-priced target triggers I've used. Here's where I need assistance.
The barrel is marked 257 x 72 Magnum . I just received the barrel action today and have not had a chance to cast the chamber however the bow is set up for around cartridge. Question anyone have any idea what the original cartridge was? I think it might've been a 9.3 x 72 R but this point am not positive. Any ideas would be greatly appreciated.

Thanks rchguns

The Eddystone rifle that I had was a .30-06.