BAD lever already covered, not Service Rifle legal. Also, I'm not 100% sure if the ambi safety is legal per the rules either, would have to go check current rules. I have seen shooters using clip-on brass deflectors, both lefty and a few righties (assume it's so they can find their brass easier).
As far as the detachable versus fixed carry handle and 600 yard elevation, there are match versions of the A4 available which have enough adjustment. It was an issue when they were first allowed, but it has been resolved. Theoretically the fixed handle might have better accuracy, but the Army Marksmanship unit uses the A4 primarily from what I saw at Camp Perry. I read somewhere this was so they can build the pinned rear sight once, and then transfer it from upper to upper as they "rebuild" the guns. Not sure if it's really rebuilding, as they reportedly don't reuse the uppers.
With respect to whether a used specimen may be "shot out", it is a possibility a use National Match AR has a suspect barrel. I figure if you buy it from a match shooter, he/she will be able to tell you about how many rounds are on it. My fear is that the rifle sitting on the used rack at a shop has burned through a portion of its useful accuracy life by being bump fired or other barrel degrading activities.
Caveat emptor would seem to apply.
Most of the shooters I shoot with figure a Wilson barrel is good for about 3000-3500 rounds of match life. The better (more expensive) barrels might go 4000-5000 or even a little more, but the Wilsons are relatively inexpensive and you can probably budget replacements simply enough. My current barrel has passed 3000 rounds now, I think my original barrel went 5000-5500 before I was confident it needed to go. I've gone from thinking about barrels as a life-of-the-firearm thing to more like tires on your car; run as long as safe, change when they're done.
Edited: Rules from the
NRA for Service Rifle. CMP rules are similar, but they do not allow the M-110 as the NRA rules do. Stainless barrels and free-float tubes are okay, gas buster charging handles, curved 20-round mags and collapsible stocks are not. And I do believe ambi safeties and those anti-walk trigger pins fall under "External modifications" and are not allowed.
