don't forget that the inside of the bolt carrier and the bolt are the essential working parts of the AR15 gas system. make sure the inside of the bolt carrier is clean and smooth, and then check the rings on the tail of the bolt. if everything looks good, insert the bolt into the carrier, hold the carrier vertical with the bolt down and see that the bolt doesn't fall out. also the bolt should be able to move within the carrier with a bit of force. the bolt is the piston in this system, it needs to be tight enough to prevent too much gas blowby, yet not too tight to move. these systems like to be run "wet", find a tiny plastic liquid dispenser, fill it with oil, and every 50-100 rounds, squirt a bit of oil into the bolt through the gas ports in the bolt carrier. the best part of this is it only takes a second because the ports are easily visible looking at the bolt through the ejection port when the bolt is forward. your rifle, being new, probably has some tool marks and tight tolerances that will polish up with use.