I took my new 300 BLK upper to the range for the first time today. It's 16" carbine length gas. I was shooting commercial Fiocchi 150gr FMJBT ammo which isn't the best stuff available. The lower I was using has fired at least 1000 rounds of 5.56 without a single hiccup including 50 rounds today. ALG ACT trigger. I only had time to put 30 rounds down range. 15 rounds through each of two 20 rd Lancer mags. Out of these 30 rounds, I had three clicks with no bang. After ejecting the rounds and loading them back into the mags, they fired without a problem. Also, the bolt didn't lock back after the last round fired on either of the two mags. Any thoughts? I'm leaning towards the ammo being the problem, but I didn't have time to troubleshoot. BTW, the ammo is loaded pretty short at a COAL of 2.06"