the 300WSM and the 300RUM?
Is there a cartridge that is between the two?

xphunter

In terms of case capacity, the 300 H & H, the 300 Win Mag, the 308 Norma Mag, and the 300 Weatherby all lie between the 300 WSM and the 300 RUM. Probably the 300 Dakota as well. - dan

From my own measurements (grains of water--fired, un-resized cases):

300 RUM 116.3
300 Win Mag 92.5

From other sources and to the best of my memory:

300 WBY 100
300/8mm Rem Mag 98
300 Dakota 97
300 H&H 89
300 WSM 86 (if I remember right)

Don't take those last numbers as gospel, but they're close. They should give you a rough idea.

Ah yes, the old water in the case trick, but that does not tell the whole story...

When you stick a 200 or 220 gr. Nosler down the neck enough to make it fit in the bloody magazine, then the wicked truth prevails...Now where sits the old 300 H&H ?? In the pound seats gents, that's where!! right behind the 300 Wby..

Ahh! The 300 Dakota. The perfect cartridge. Based on the .404 jeffries like the .300 rum and wsm, its sized to fit a standard length action. The same capacity as a 300 weatherby, with a shorter, fatter, efficient, powder column. Forget the RUM, get the Dakota! You can get close to RUM velocities with a 26" barrel and a standard length action.

Ray is (almost) correct that it is only after accounting for the space taken up by the bullet when seated to touch the lands that the EFFECTIVE case capacity can be calculated. He is also (almost) right that a .300 H & H has about as much effective capacity as a .300 Winchester, if the H & H is built on a magnum length action and the Winchester is on a standard length action. However, if the Winchester is on a full-length action (like my Sako), then its effective case capacity exceeds the H & H appreciably.

The WSM, being built on a "short" (medium) action, has VERY restricted case capacity when using very long bullets. Using bullets of more than 180 grains in the WSM causes rapidly diminishing returns. As a matter of fact, I would guess that a regular .30-06 Sako with its 3.6" magazine would give equal or superior velocities to a .300 WSM (loaded to the same pressures and in the same length barrels) using the Nosler 220 that Ray is so fond of.

If I was going to rebarel or put a custom .308mag together it would be the .300 Dakota. I have a 7mm Dakota & find I can run right along w/ the STW in a std. length action & a bit less powder.