Problem with the SAI is that they started using cast parts about 10-12 years ago, & current production has LOTS of cast parts now. And, they just don't hold up as well as USGI parts, which are forged.

If I were shopping for a rifle today, I'd look for an older one with most/all USGI parts. The best standard USGI barrel you can find will be an SAK, made by Saco Defense, Saco, ME.

Neal