With the interior being tighter, it might also end up with exactly the same capacity as the .303 case.

Interesting project Lancaster - J.J. Donnelly's book on CTG. Conversions shows similar conversions.

I think that's going to be a fun round, Frank. The RCBS 250gr. cast with G/C has been very accurate for me in several .375's, as-is the 269gr.G/C Lyman bullet.

Lyman also has a Silhouette bullet of well over 300gr.