You may be surprised with any factory ammo not just the WSM’s !!!
I have chronographed factory ammo because I’m aware of the difference one might see.
One reason is due to difference in barrel length. Most all factory figures are taken with a 24” barrel.
A second is how we measure the velocity. Sitting a chronograph 10-20 feet in front of the muzzle does not give the muzzle velocity. Factory ammo is either measured from the muzzle or corrected to the muzzle.
Another possibility that can change things drastically is when the factory uses a pressure barrel to take the readings.
And lets not also forget variables such as air density, bore condition, and as some around hear have alluded to, our position in relationship to the equator !!!