Well, the thing is that I've been offered a Mark V action, i.e. clean without any barrel or stock.

So I was wondering if it's possible to open it up to the most awesome Weatherby magnums since I have an almost ridiculous desire to acquire one of the calibers based on the mighty 378 case. Not that I have to but...

The 378/416/460 magazines are 2 round single column magazines. The fact that Weatherby had to go this route tells me that getting a standard belted magnum magazine to work would be very difficult. You could of course by a new magazine but I believe they are quite expensive.

Also the 378/416/460 actions have a notch on the right rear of the receiver ring to allow unfired cartridges to eject (the 378/416/460 OAL is longer than the 300/340 rounds).

If you can get around these problems and have access to a lathe you can always turn down the rims to match the existing bolt face. Time consuming, but you only have to do it once and you can leave the bolt as is.

It can be done. First set the bolt up in a mill and lengthen the boltstop cut (ie the bottom flute). Then open the bolt face and adjust the extractor to work with the larger case.

Buy new bottom metal as mentioned above. I'm not sure that the cut in the bottom of the receiver even needs to be lengthened to accept the new magazine. Good luck

Yes this can be done. I have had it done you need a new magazine box, follower, and extractor. Than when I got it all done I turned it back to a .300. I have a left hand bolt thats ready to go.

I sincerely thank you Gentlemen for your replies!

So this means that about any cartridge would fit into my Mark V action then. I could even make a 500 A-Square of it which is very interesting. Also a 585 Nyati.

The question is: what do I need, and what do I want? I already have a 222 Rem, 300 Win Mag, 358 Norma Mag, and a 458 Win Mag. I could see a 378 Weatherby in there. But also a 416 Weatherby. Or maybe a true big bore like a 500 Jeffery, or a 585 Nyati. I don't "need" anything really. So the caliber choice is quite weird.

Suggestions are most welcome. Do keep in mind that this is a Mark V action so a 30-06 simply won't do

I guess no one is particularly interested, buuuuut, I've now decided on a 375 Remington Ultra Magnum for my Mark V action.

The 375 Weatherby would've made more sense as this is a Weatherby action, but the Weatherby is more expensive both when it comes to shells and reloading dies.

Moreover, the 375 RUM is a very harmonic cartridge. It feature no unnecessary magnum belt, and it has a logical 30 degree shoulder.

One objective is to dwarf my uncle's 375 H&H

The other is to find the ultimate cartridge for everything. I already have the 358 Norma Magnum which is pretty close to ideal for everything on this planet. But with the 375 you take a quantum leap towards THE ultimate cartridge, since the 375 can be used when hunting buffalo in Africa as well.

Sure, you could use the 358 for this in some countries. But with the 375 there are no questions asked. Not that I plan to do any buffalo hunting in the near future. But I figure that the ideal cartridge features the biggest diameter bullet, with the highest bullet weight, exiting the barrel at the highest velocity.

I think that the 375 RUM / Weatherby come pretty close with all these aspects taken into consideration. Especially if you want to survive recoil as well. With a little (or actually, a LOT of) practice, I will get used to the recoil and enjoy it.

Although I know that everything I've every heard about recoil is more or less bullshit, I simply DO believe that the 378 Weatherby is a bit too much for me.

550 express or 550 magnum...

don't bother with the small stuff....

jeffe

Hehe, good point Jeff!

But I would never get a license on anything above my 458 (that's what the lady at the police told me).

And I, no offense, really do think that a 375 will be a lot more useful for my hunting needs than a 500+ caliber.