Had a failure to extract

[tireys]

I had a couple failures to extract this past weekend when I was shooting my rebarreled 6.8spc II upper. I put a DEZ 18" mid length barrel on my receiver which is a 1/10 spec II chamber. I am using a W/C NP3 coated bolt and carrier group, BCM micro gas block and I was shooting factory SSA 115gr. OTM. The mag was a fairly new C- products 15 rnd. I assembled this without a headspace gauge because I don't have one. This is what I suspect the problem is but, what do you all think?

 

[insight3b]

Besides the HS gage the next thing that comes to mind is the gas block aligned with the port in the bbl properly? An easier way to determine this is by looking at the gas tube where it interfaces with the carrier key you have to remove the bolt from the BCG to tell. The charging handle should just bump the gas tube last 1/2 inch of its travel then slide home. If there is more resistance than a slight bump when sliding the charging handle back home then the gas block is probably off center just a tad...with a small hole like the gas port even slighlty off center gas block greatly reduces the amount of gas getting back to the carrier key