Depends on how custom you can go the 300 Hulk or 300 JAzz is the way to go. The 300 hulk is a shortened 338 Lapua necked down and the 300 Jazz is the 338 Norma necked down If I remember right. Tom Starver, the advocate of the Hulk claims 3000fps with the 240SMK and 3500 with the 208 Amax.

I have shot both the RUM and WM and the 208 and 210 bullet is the best for the case size in my opinion. You can drive the 208 amax and 210 Berger fast enough to pass the 240SMK. I tried the 240SMK and I could not get the speed that I thought I needed in order to make it a better choice than the other two I mentioned. This winter though I am going to try the new Hornady 225 and the 220 SMK see what happens.

Good luck
Kdog
Provided is some information on the 300 Hulk.

http://www.longrangehunting.com/foru...e-brass-22352/