Lobo....While I did do the workup and design of the .416 Beartooth due to requests from the forum, I have not really gooten into the converting any model Marlin except the .45-70's.
To give you a little background on both the .416 and .375 Beartooth cartridges.
Well before the .450 Marlin came out. Sonny Youngblood and I were playing with the idea of putting Frank Barnes .458x2" on a Marlin 45-70 action. Dummy cases were made up and we found all the feeding worked. About that time the .450 Marlin came out and we shelved the project.
Later the subject came up on the forum and I did the design and pressure work up, based on Marshall suggestion and designed around his cast bullets. Some members on the forum felt I should have moved the shoulders forward to get more case capacity. The entire concept was to have enough neck to cover the lube grooves. Although jacketed bullets can be used, it was cast bullets the design was based on.Both the .375 and .416 Beartooth cartrides will feed through an action that was a .45-70. However, the actions set up for .35 Remington would be too short, etc. Both cartridges have, more or less, died on the vine.
Best Regards,James