I purchaced what I was told was a brand new Bushmaster M4 from a local dealer. It's an A2 w/ bird case flash hider and 4 position telestock. I got it in different light at the range and noticed the upper receiver and barrel have some wear on the finish. As it turns out, I know for sure that he ripped me ff badly on some magazines. Now I'm wondering if this gun was pieced together using old parts on a new lower and sold as new.

The marking on the lower are:
-Mod xm15-e2s
-Bushmaster logo and serial number

There are no obvious marking on the upper, which is the area I'm really curious about..

The barrel says  8 MP Nato 5.56 1/9.

sorrt I realized I posted this in the wrong forum.

Contact Bushmaster Customer Service: 1-800-883-6229.  Provide the ser # and they will tell you if it was built up from a stripper lower or if it was manufactured as a complete weapon.

Quoted: The barrel says  8 MP Nato 5.56 1/9.

That should be "B" MP Nato 5.56 1/9