I have a .375 -.303 I made from an old shot out (really bad bore!) Martini-Enfieild. I had the original bore reamed and rifled and the chamber openned with a neck to accomodate the .375 bullet. I have formed the cases out of heavy brass boxer primed .303 military brass and anealled the necks. I have not had time to load any test loads yet. I will need to do some sight work later, as the original rear sight is not very good condition. The original front sight of the carbine was battered almost gone. I had a dovetail milled and an "ivory" bead put on. More as I can.
I am excited about the cartridge potential.