Last year I built a wildcat 7mm based on the 300 WM cartridge. But it is not just a 300 WM sized down to 7mm. The shoulder angle is increased 10 degrees and the shoulder is blown our about .003. The neck is also pushed back to allow for a full .284 length neck.
Shoots very well with velocities comparable to a 7mm STW.
I have the reamer and while I wouldn't part with it I could be persuaded to loan it out it you are interested.