But the .300 RUM seems like what we already had, a .300 wby?
Not really. First the 300RUM doesn't have the useless belt on the case. The RUM case has about 15% more capacity than the WBY mag so it is able to produce higher velocities if you reload. The only problem with the RUM is that factory loadings are pathetic. This is so with all the RUM factory loadings. [:'(]
For instance Federal lists the same 180 grain barnes TSX as 3150 in the RUM and 3110 for the WBY.
But in hodgdons reloading manual they list the same speer SPBT at 3300 for the RUM and 3171 for the WBY.
Can you get a .300 RUM that much cheaper than a .300 wby?
Yes, ammo is generally 10 - 20 dollars cheaper per box and a Remington 700 is generally a heck of a lot cheaper than a Weatherby MK-V.
In a 30 caliber magnum Iprefer the 300WSM over the RUM, Win, WBY. I am no fan of belted cases unless the belt is needed like on the H&H cases, 458 Lott &Win, etc...
IMO the RUM is too much of a good thin. It has too much case capacity for the .308 bore diameter. IMO that muchcase capacity is better suited to .338 and larger.