jladams,
I have had four WSM's (still have two), all 300's and they exhibited the same symptoms. Extremely sticky bolt lift with Win ammo, but shot fine with Federal. I think the issue is the Win cases are "short" to the shoulder creating quite a bit of headspace, combined with a stout load and maybe a lack of elasticity in nickel plated cases. When fired, the firing pin drives the case forward in the chamber until it hits the shoulder of the chamber, while the violent exlplosion of the powder ignition drives the casehead back to the boltface. Rapid and excessive expansion in lenght causes the sticking (that's my theory).

If you can, repeat your mesurements on before/after to see if it's a headspace issue, but you'll need to do two things:
1. deprime the fired brass - if your primer is sticking out a little or if you have firing pin flash around the pin strike, it can affect your measurement.
2. If you don't have a stoney point tool, use a deprimed fired pistol case (like a 40 cal) to slip over the neck so you are measuring at the datum line on the shoullder (about the midpoint of the shoulder), then zero you calipers for the length of the pistol case.

I often see 7 thousands length expansion on new WSM cases, and get some heavy bolt lift on first time fired cases (they come short from the factory), but they shoot great second time through the reloading cycle, after sizing to correct headspace in my dies....

In factory ammo, they're loaded stiff..... And you may want to stay away from the nickel plated stuff - the case is not as elastic as brass.
Elkbane