Truthfully I don't expect alot of improvment, but I love my other improved cartridges and the long brass life. Possibly a 338 excalibur necked up to 375. I have plenty of other guns for typical hunting so it's more of a venture in to extreme long range.
In my opinion the Excalibur is about the ultimate 338. But it needs a larger action than the 700
At one time I looked at necking it up to 416 because of case capacity and with the requirement
of a MK 5 or a custom action plus the cost and availability of brass and loading equipment it
more than tripled the cost.
The 416 buff will push a 400 grain bullet almost 2700 ft/sec without being overloaded and case life
of the 416/375 is very good.
Without a Muzzle brake it is just about all the recoil I can deal with and after 40 or 50 rounds
at the range the fun has gone out of it.
I also designed a 338 super based on the 375 RUM brass because it is available and works
in a magnum bolt faced 700 REM. It has been improved and the capacity increased to 115
to 119 grains of powder (Depending on what powder).
Testing is still on going but it appears that case capacity may be unusable, so the standard case
may be the way to go for the .375 bullets.
Rather than improve on the 375 RUM I would elect to go with a 378 Weatherby and a mark 5
Just an opinion, But it is fun to play with different ideas.
Keep us posted on your project.
J E CUSTOM