What does Springfield say it will do? I shot M1As/M14s for many years in National Match Service Rifle competition, so have some experience with these in their match guise. First thing to remember with the M14 family, is that they are Service Rifles; they weren't designed to be accurate first and foremost. They're rugged, easy to strip down, stone-cold reliable and that's what they were designed for. Accuracy standards for the rack grade issue guns, if I recall correctly, were around 3 MOA. The National Match modifications brought thos down to right around 1 MOA after some TLC, a good barrel and a proper bedding job. This is about what I'd expect to see from a "National Match" version like the one you're looking at. When I was with 5th Army MTU, the rifles they built wre fired from a machine rest and were exepcted to hold right at 3" 10-shot groups @ 300 yards. I saw the occasional rifle that would do 2.5" or a little less, but in the long run, you're looking at right about 1 MOA as an average. That may not sound too sexy when everyone's talking about bolt guns that will consistently shoot 1/4 MOA, but again, they're entirely different animals. Ammunition here is another thing to consider, as it's likewise considerably different than that used in bolt guns. For what it's worth (and that should be a bunch, considering the source) the Lake City M118LR ammunition requires a bit under 1 MOA for acceptance; ten 10-shot groups @ 300 meters, average group size not to exceed 3" extreme spread. Most do much less than that out of a bolt gun, but that's still what the military will accept, and that should give an idea of what they'd want out of the M14/M21 as well. Incidentally, if you start loading for this rifle, DO NOT use the same techniques you'd use for a bolt gun. Most will gain you little or nothing in terms of accuracy, and some can be downright dangerous in the gas gun. Go to some of the National Match competitive sites/forums for the details here.
I earned almost half the points that went into my Distinguished Rifleman's Badge with the M14, and so will admit to a special fondness for it. It's a great rifle and I'm sure you'll enjoy it. As for myself, nostalga has to give way to pragmatism, and I've been shooting the AR-15A2 for my matches ever since the early 90's. Full disclosure requirements duly satisfied, have fun, you'll like the old girl.