I think a Savage action would be a good, cost effective candidate for your needs. You would be able to put it together yourself on a budget and have great options for triggers, barrels, stocks/chassis and the like. I'd buy that model 50 from you for a good price too - my dad hunted with one until it was stolen from his truck in the 80's, but that's not the reason for this post. I don't recommend the Mausers for LR/ELR plinking unless you're very steady on the bench - that long lock time does cause your POI to shift around - I've gone this route and now use a Savage 110 action as the basis for my long range plinker with a single stack magazine simplifying the cartridge feeding needs and good presentation into the chamber. Barrel swaps are a breeze too. Pick a cartridge, buy a pre-fit barrel and a set of gauges and you're off to the range for some trigger time in less than 30 minutes. Short or long cartridges will require the appropriate mag, but that's easy as well. Whichever path you choose - have fun, enjoy the journey and be safe. We learn best by doing. There are great people on this site to guide you in the decision making processes and to help iron out the kinks - and there can be lots of kinks with these mechanical projectile launching contraptions