I also have never had a problem aligning the gas block/gas tube on an AR15 or AR10, but YMMV. It may be a gas issue, but this thread reminded me of a customer that brought 2 AR15s (5.56NATO) he recently assembled, and neither would cycle. I took his uppers off, and tried them one at a time on one of our lowers at the shop, and they ran fine. Turns out "Mr Assembler" ordered .308/AR10 Buffer springs & weights.....no bueno. Not saying that's the case here, but one more thing to check if it's not the gas part of the operation. -Tom T
