The 338 Kubla Kahn is made from the parent case of the 338-378 Weatherby. It has a 30 degree shoulder rather than the double compound radius of the 338-378. There is a small increase in case capacity of around 8 to 10 percent.
Both the Kahn and the 338-378 are significantly larger in case capacity than the 338RUM.
Here is a picture of all three, left to right, 338RUM, 338-378, 338 Kahn. All three are loaded with 210grn TSX bullets. [image]
For a comparison of velocity between the Kahn and the 338RUM, just use the 338-378. For example out of the Barnes manual: 338RUM 200grn XFB, highest listed vel. 3186, 338-378 same bullet, 3338. And for real world, with my HP Precision 338RUM I can get 3250 out of the Barnes 210 TSX, with my 338 Kahn I can get 3500. I am getting 3150 with the Kahn and 250grn SMKs.