Pictures taken and posted below.

I owned all 8-9 of these actions at one time. Somehow I missed that this one is NOT marked as a Mark X.

Pics will show that the action and magazine have been enlarged in comparison to the .300WM Mark X I have on hand. I also measured the rail spacing, and it is wider at points, which would be needed for a .375.

Why a 7mmRemMag barrel was hung on this action is a mystery. Sitting it aside for now, as do not want to put the time into stocking it, to then find it won't feed 7mmRemMag properly.

In all pictures, the notched/enlarged action is the one on the top.

NOT a Mark X