I had a guy come by my shop today for some help getting a stuck case out of a AR pistol upper. I won't say the manufacturer as in the end they did more than right by the guy. He ordered a pistol upper in .300BLK. He got one new in the box, with the box marked .300 BLK. He took it to the range and on the first round the gun exploded, destroying the lower and blowing the back of the case off leaving the rest fire formed in place. What they shipped him was a .223 Wylde upper. The barrel was marked but the stamp was between the gas block and receiver right under the gas tube so dang near impossible to read without removing the quad rail. Could have been a whole lot worse as the bullet made it out the barrel, it appeared to have "cored" the round shaving off the outter jacket and just pushing the lead core through. Anyway just remember humans make mistakes, take nothing for granted.