I think you should build a long action caliber with cartridge that has about the same case head diameter as the 8mm mauser. If you don't, you will need to change the bolt head, ie cut away metal. This would be the case for the .300 WM, 7mm Rem Mag, and many of the other calibers mentioned. You may also have to adjust the length of the magazine if you go to a longer cartridge or a shorter one. You cannot fit a 8mm rem mag, or .375 H&H in a 98 mauser magazine. They are too long. Similarly, a .308 or .243 will be shorter than ideal and may require shortening or blocking the magazine.
.22 swift, 6mm Rem, 6.5x55, 7mm mauser, 8mm mauser or their wildcats will function very well with minimal changes to the original gun. Cartridges based on .30-06 will do well also. These include .25-06, .270 win, .280 rem, 30-06, 338-06, 35 whelen and a few others.
If you want bigger than you already have, build a .35 whelen. It is a classic 98 conversion caliber and a serious cartridge for anything in North America. Perhaps the most common conversion is a .30-06. I know you have one, but it is a great cartridge for most hunting. There is nothing wrong with going a little smaller and having a rifle that is pleasant to shoot as well as look at. I'd really consider a .25-06, .270 or 7mm mauser in this case. Certainly the .25-06 and .270 will be easier to find ammunition for.
.22 swift, 6mm Rem, 6.5x55, 7mm mauser, 8mm mauser or their wildcats will function very well with minimal changes to the original gun. Cartridges based on .30-06 will do well also. These include .25-06, .270 win, .280 rem, 30-06, 338-06, 35 whelen and a few others.
If you want bigger than you already have, build a .35 whelen. It is a classic 98 conversion caliber and a serious cartridge for anything in North America. Perhaps the most common conversion is a .30-06. I know you have one, but it is a great cartridge for most hunting. There is nothing wrong with going a little smaller and having a rifle that is pleasant to shoot as well as look at. I'd really consider a .25-06, .270 or 7mm mauser in this case. Certainly the .25-06 and .270 will be easier to find ammunition for.
