Well the .375 already exists. The Germans made the 9.5X57 way back in the 20s and maybe before. It's not popular, but it's still around, and I am told my one owner in Reno Nevada that when used with the 235 grain Speer bullet it's a super effective deer killer.

So with the standard German 57MM case we have the 24 caliber 6MM Remington, the 25 caliber 257 Roberts, the 26 caliber 6.5X57 (and it's near-twin the 6.5X55 Swede), no 27 caliber, the 28 caliber 7X57, No 29s 30s or 31 cals on that shell, (but the 7.65 Belgian is a 31 cal Mauser shell, just not THAT Mauser shell) the 32 cal 8X57, no standard 33 or 34 cals, then the 35 caliber 9X57, the 36 cal 9.3X57and the 37 cal 9.3X57.

I have re-barreled 3 Mausers to the 9X57 for customers, but I had a reamer made with a pilot to go with American size 35 cal barrels so they are made for use with our .358" bullets instead of the German/Austrian .356" bullets. Sure makes ammo a lot easier to obtain in the USA, with no more then a set of dies.

I have a swap-barrel rifle started right now on an FN Small Ring Mauser with 2 barrels, each with their own forends and sights as well as scopes. The set also comes with a hand press and 2 sets of dies, one for each caliber and a shell holder. The 2 calibers are 257 Roberts and 9X57. And my 9X57 will use American and Australian .358" bullets. So it's a 25 and 35 caliber rifle set, and should cover nearly every need for a North American hunter. Both barrels will be zeroed with loads that will come prescribed with the set, so if the owner follows the recipes he can simply load the rifle with their individual barrels and the scopes and sights will strike dead on. The gun comes with 100 rounds of each ammunition for each caliber too. So the owner (who ever buys it) will need to buy powder, primers and bullets for future ammunition. I'll zero the 9X57 for 150 yards and the 257 Roberts for 200. I'll zero for the 225 grain .358 Nosler partition with the 9X57 and with the 110 grain Nosler Accu-Bond with the 257 Roberts.

As you might guess, I also see a LOT of merit in the old Mauser shell design.