You can stop wondering - A lot more is needed, for conversion to a belted magnum.
The bolt face would have to be enlarged to fit, and the extractor claw altered or replaced with a commercial one from a magnum.
The cartridge feed shapes, forged into the lower side of the receiver at the magazine well, would have to be expertly altered to feed the belted magnums w/o letting them all pop out in one bolt cycle, or jam.
It would be a good idea to re-inforce the stock against splitting, in between the recoil lug & magazine well, between magazine well & trigger, and also at the rear tang.
Is it a military Mauser? If so, R U gonna wanna scope it ?
If so, it'll now also need D/T for scope mounts, the bolt handle altered to clear a scope, & ditto the safety.
Those conversions were done back when factory magnums were costly, gunnies poor, and cheap Mausers plentiful.
Today, IMHO, you'd be better off starting with a commercial magnum action if you want a .338, ans a standard action if you want a standard cartridge - unless you have a lot of time, money & expertise.
If you want to play with converting your Mauser to something,it's a lot easier to go with a cartridge that has the same size rim & length as the one original to your Mauser - BTW, it's a large ring M-98, right ? :
If you just want a .338 of one flavor or another, you could build a 338-06 quite easily. Just about anything that is 30-06 based such as the 338-06, 35 Whelen, 280 Remington, 270 Winchester, 25-06, etc. will work quite nicely in a '98 mauser.
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