Watch out for M14s, especially those "assembled from parts." There is one manufacturer currently making M14 receivers in correct,legal configuration - may be Smith, though it could be another. But, other than that, an M14 is considered to be a machine gun, since the original receivers were able to be made full auto. (Remember the BATF "Once a machine gun, always a machine gun.") Any M14, other than the one being current, would have to have Class III paperwork and tax. BEWARE OF REWELDS! There are some out there which have been rewelded from demilitarized M14s. I saw one at a gun show a couple of months ago. Fortunately, I checked battlerifles.com , an excellent source of M1A/M14 knowledge, and was put wise to it. The reweld would be illegal. There are also tales (many, corroborating each other, so it sounds legit) of people having bought what they thought were legit M14 remanufactures only to find they were to be confiscated by BATF because they were
illegal machine guns.
Bottom line, buy an older - meaning 2 years or so - M1A. Look for GI parts, especially bolts and operating rods, etc. The current crop of Springfields, I understand, are using a lot of "newly manufactured", meaning not GI parts, some of which may not be as good a quality as the GI.