Two recent experiences with "commercial" carbines:
AO: picked it up off the rack at a gun store, and tried to check out the sight picture. The ventilated metal handguard was so out of spec, you couldn't see the front sight post! Might be tough to shoot that one...
Universal: Watched a guy try to shoot a 3-gun match with his carbine. Must have mis-fed over a dozen times. While it could have been a magazine problem, I wonder....
Do yourself a favor, and go USGI. People have been saying that for years, and there must be a reason. As for warranty concerns - do a good job inspecting the rifle at the start, and be prepared to replace worn parts as needed. They aren't that expensive, and there are a bunch of online vendors selling them.
I got mine from Charles Hadley of South Portland at one of the many gun shows he frequents. He's the guy with three tall racks full of M1 Carbines. You can call him to discuss carbine choices, but be prepared for a long phone conversation - he is the local expert, in my opinion.
