I am starting to hear that velocities for the 300 WSM are not as close to 300 WM as was originally thought. Can anyone verify?

I have chronographed factory loads for both the WSM and WM for other guys at the range, and they have been pretty much neck and neck. In fact, I chronoed a Heavy Mag load that was actually slower than the WSM.

Handloading may show a bigger gap, but I don't know for sure.