As far as rejects, it's been known for a LONG time that XM type ammo (Federal and AE for example) has been rejected by an inspector at some point and the round has been broken down and reassembled and repacked for commercial sale..
Yes, but many people don't know that. They sell it like it's just as good as what the military uses, when in fact it was rejected for QC purposes.

As stated, get a case guage and if it guages, shoot it. I have about 3K of "Israeli battlefield pickups". It looks like hell, but it guages and shoots fine. It didn't cost me half of what XM costs though.