Choices for bottommetal material: 
Commonly used choices are leaded stock and structural steel.  

Leaded stock is not inexpensive, but it machines beautifully and the lead acts as a self lubricator.  In short, tools seem to last forever and very easy to polish.  It also dents easily and the lead inhibits long lasting rust blue. 

Structural Steel is cheap, machines pretty easily, polishes well...not a bad choice, but tends to have voids that usually do not show up until the final polish. 

At CGRS, we use the respected low carbon steel known as alloy 1018.  1018 is moderately expensive, very tough and in its annealed state has more impact resistance then 4130.  1018 is tough on milling cutters, tough to polish, but engraves and rust blues beautiful. 

We also took a close look at the available products and saw room for improvement.   Competition bottom metal for a 375 H&H on a 98 Mauser had an extremely deep profile at the front guard screw   area, making for a fat and unattractive fore end shape.  Proper "stack" results in the same capacity and we were able to reduce the vertical depth near the front guard screw by almost 100 thousandths inch.  Extend that out to the fore end tip and you will now have a slim, trim profile. 

A favorite caliber of mine is the 500 Jeffery.  Competition made the magazine box so deep that an extra long trigger (their own) was required.  Proper stack resulted in the same capacity, but uses a standard non-proprietary trigger with graceful stock lines. 

Please, do not forget trigger guard shape.  Ours is graceful, modern but gives just a little more finger room, as delivered, our units are hand polished to 120 grit. 

At CGRS, we simply will not compromise quality, design and material.  We are comfortable in offering a 100% money back satisfaction guarantee!