The biggest single difference between a rack grade and a service grade is bore conditon, Look at the CMP web site , they'll tell you that the service grade rifles will have a bore that will have Throat erosion less than 5, and Muzzel wear less than 3, Rack grades may, and often do have alot more wear on the bores, alot of guy buy them with the idea of rebarreling them in.308 and buying a rack grade offers them a way to get .308 rifle,The last service grade rifle I bought has a bore that is, just about new, If buying sight unseen from the CMP, and want a good shooter I'd get a service grade, If you could go to camp perry and look before you buy I'd give the racks a good look as well, A friend of mine and my self went there before the matches and he bought a rack grade rifle that has a T.E of 2, M.W. of almost1, in other words the barrel is almost new,when we cleand it out, the bore was like a mirror inside, only thing wrong with it was the receiver was turning a plum color, other than that nothing was wrong with it, hell, the stock was pretty nice as well,excellent deal for $400 But like I said if you're buying sight unseen I'd go with a service grade, you'll get a rifle with a good bore and should be a good shooter.