Gunsmithing 375 Ultra magazine options

[Muskox]

Aside from using a perch belly drop box integral bottom metal like Duane Weibe makes or Sunny hill, is there a way to fit more than 3 375 Ultras in a m700? Is there an AICS type system that would work?

What about the HS Precision magazine system?

 

[Powermac]

A Long action DBM using 338 LM, or 338 LM CIP mags.
Seekins or CDI for example can deliver you those.
ANd the mags can be made to fit, might have to modify the feed lips a bit.