Gun Doc, I have 2 P64 Magnum action that is used for my 7mm Mashburn Super and the other is a rechambered 300 Weatherby that started as a H&H. It feeds and ejects excellent, the 7 Mashburn Super seems to be good so far as well.
I have converted a few of the Classics over to 3.6" boxes in order to do exactly that, load rounds longer and utilize the Mag space. I never had any trouble with how they ejected at slow or fast pace with the shorter bolt stop, but do see where the shorter bridge on the rear would assist getting the case clear of the rifle.
Have all of the parts and pieces been polished and smoothed in order to function smoothly? I know if the ejector doesn't move up and down freely it'll give you headaches.
Your cartridge sounds a lot like a 300 Weatherby, or if using the 300 Win case for it, something like a 300 Mashburn Super. Not sure which direction you are going with it but It sounds pretty cool.
Hope some of the others have better info for you. I believe the slot in the top of the actions is merely a clip slot and serves no purpose for function. The smart folks will correct me if I am wrong.
