Tom,

Need to clarify a couple things. First off, the Ruger MkII Sporter comes with stainless steel barrel/action, and a laminated wood stock. Unless they've made something not in their current catalog, nor on their website, they don't chamber it in 300WSM, but do make it in 300Win.Mag., and the barrel length is 24". Following are specs from the Ruger website:

Caliber: .300 Win Mag
Capacity: 3 Rounds
Finish: Stainless
Stock / Grip: Brown Laminate
Barrel Length: 24"
Groove: 6
Twist: 1:10" RH
Overall Length: 44 3/4"
Weight: 8 1/4 lbs
California Approved: N/A
Massachusetts Approved: N/A
Front Sight(s): None
Rear Sight(s): None
Other Features: Three-Position Manual Safety
Suggested Retail Price: $ 773.00
Miscellaneous: N/A

The stock Ruger trigger will generally require some work by a gunsmith to lighten it up some, or can be replaced with a Timney trigger, etc. However, I have found a few on the shelves at my local dealer who's triggers were useable out of the box - not good, but useable. The integrated system for attaching scope rings on the Ruger is one of the best, and of course, saves you money as you don't have to go out and buy rings and bases. I don't know about "lapping" the rings, I never have, and I've had no problem with mounting scopes on the Ruger rifles I've had.
Is it a shooter? Will you have to have the barrel floated? No way to answer these for sure. Every rifle is different. Most Rugers I've had have been good shooters.
I like some Remingtons, Winchesters, Sako, etc., but for my money, if I had to limit myself to only one rifle [] I'd take a Ruger first.