Got a couple of M48 Mausers into the shop this week and the discussion started about what caliber to build with since the mag box is too short for 30-06 length cartridges. The .350 Remington magnum came up and that looks like a pretty good brush gun/300 yard hunting cartridge. It's not very popular and never seemed to catch on but it is in the same neighborhood as the 35 Whelen. What do ya'll think? Good or bad?

Why not! Or maybe a 35/284. either way the bullets could be seated out and gain powder space.

I think the 350 Rem Mag is an excellent idea! Run a hot load with a 250 gr bullet (something shorter like a Partition, Aframe, or Woodleigh), Norma 203B, and a 18-20+ barrel.

Or you could go different and build a 9.3/.350 Remington Magnum-I believe this is called the 9.3 Barsness-Sisk (BS). Should give you close to 9.3x62 ballistics. Just s thought.
Or you could neck up to .375, .410, 416, .423, or even .458. Your belt would allow you to not worry about narrow shoulders and be as creative as you wish.

The 350 Rem is an excellent cartridge in a medium action. Your magazine should be long enough to allow some of the excellent 225 gr bullets such as the Nosler accubond to be seated out a little. This is not just a close range calibre when you can use the 225's.