I have a 16 inch x39 build I completed a year or so ago that has something like 1500 rounds of steel case through it and has run flawlessly. It has been great. And with Hornady Black is actually an MOA or better rifle.

So I decided to build an 11.5 gun. Both are CLGS, using an A5H2, RCA BCG (which uses a true x39 bolt and not a hogged out 5.56 to provide good firing pin protrusion) and a LaRue MBT (which has a full power trigger spring.) The only difference was the gas port size. The 16 inch is .093 and the 11.5 (which arrived woefully undersized at .078) I opened up to .089 to start, figuring decreased dwell time might come into play so I wanted some room to grow if need be.

Off to the range a few weeks ago along with a SICO Chimera for fun. Using a variety of steel case to include Tula, Red Army and Barnaul. First five rounds go click but no bang. Hmmm. Primer strikes are deep and even. Load up another mag. Finally get a few to go bang but more that don't. Take the can off. Same results. Side note, when the rounds DO light off the ejection pattern, both suppressed and non suppressed are good to go ranging form 2:00 - 4:00 ish ie nothing I am going to get hung up on chasing down.) So at this point I am thinking BCG. Take the one from my 16 inch, which I know works, and swap it out. Same results. Next I swap out the hammer spring because who knows? Nada. Same results. I had no brass case on me so left the range with a big old WTF. I mean I could understand if it was ONLY the Tula or the Barnaul but it was doing it with all three brands and out of the same ammo can that shot fine in my 16 inch gun.

Fast forward to this past weekend and after getting 100 or so rounds of PMC Bronze I go back to the range. Everything cycles, everything goes bang, runs perfectly. Everyone who I has seen the ammo (gunsmiths, ROs and dudes who are in the know) all think the primers were struck well enough that they should have gone off. So the assumption is at this point it's an ammo issue. But I keep going back to it happening with all three brands from different lots. So my question is, what did I miss in my trouble shooting? Or is this just a fluke?

Note - Failure rate on the Russian ammo was roughly 30%