Just curious. Did this setup have the gas block vent hole welded up?done by IGF, uses the factory 16 inch gas block
That gas block is US made sold by Adam over at HKParts, its not a real true 416 10" gas block. Also port size on the barrel isn't the most important issue as its the port size on the gas block itself that matters and that varies between 416 gas blocks.
Are you running the HK buffer and HK spring?
Yeah, I'm realizing that. Too many variables. I'm gonna go back to my old setup.
Speaking of HKParts, they are now listing HK416 10.4 vented gas blocks for sale. They list them as HK OEM parts, not as HK "style" parts like the barrel kit they also sell.
HK416 10 Gas Block
This may solve the OP's cycling problems.