I finally adjusted the shoulders of the Ten=X case by a very slight swage of the angle with the base of my 12.7X44R die. It flattened out the angle just enough to chamber. Ten-X has offered to give me a few empty new cases in exchange for a Fired case in my chamber of the .577/.450. They were very interested in making sure they have usable ammo for most shooters.
TODAY, Finally, after months of ownership, I made it to the range and fired a few rounds.
The Ten-X ammo is loaded with a healthy charge of Hogden777 powder and a missle cone pointed shape 480 grain bullet. Man!! This light sporter does have some authority at both ends and jumps off the bench!! Once I figured out sights (obvious I needed a much higher front), I used the bottom of the target as an aiming point and put 4 shots in about 2 1/2 inches at 50 meters. Not good, but not bad for random loads. Now I can start to tailor for the rifle.
My son shot my Martini .310 Cadet with some of my loads. He shot some very respectable open sight groups. This is the first time he shot it. Martini Rifles, Large and Small. PHotos later.