Solitar. Somehow, I seem to be missing the point. You apparently want a .300 Magnum of some kind, but don't want barrel erosion. Any good barrel will last at least 2,500 to 3,000 rounds if treated properly. Granted, if you shoot as fast as you can, you will burn the barrel out in short order.
At the range, if you give your rifle a minute ot two between shots, allowing the barrel to cool, it should last quite a while. About the only time I could see really rapid fire, would be at an animal that you were trying to bring to bag, and if you do your part, well the first shot should do the job.
About the only other time rapid fire might be needed, would be in a rifle match, and I don't know enought to comment on that, but I don't think many .300 Mags are used at the shorter ranges, but are at the 1,000 and farther matches.
2,500 to 3,000 rounds is a lot of ammo. You can have a new barrel installed for about $300 blued and maybe $100 more for stainless, but if you shoot slowly at the range and let the barrel cool a bit, it will take you a while before you need a new barrel. Think about it.