I had a cheap Aero lo profile fixed gas block laying around and drilled out the grub screw hole under the port to .220 so I could get a tap in the gas port. Used a .165" bit to open the port hole up, and a M5 x 0.8 tap to thread the enlarged port hole. This allowed me to thread the grub screw that no longer had a home into the port hole effectively closing the gas off. Then I drilled a hole in the center of the grub screw with a 0.69" jewellers bit effectively reboring the gas block to .069". This worked like a charm. I was prepared to open the hole up progressively using .073, .076" bits until the gun locked back suppressed but not unsuppressed. I think the .069 might be perfect. Doesn't lock back unsuppressed, but locks back suppressed. A5H3 buffer. I thought about loctiting the "gas port carburator" with 620 green but it can't go anywhere. It's captured by the barrel and the top of the gas port, but I can still unscrew it if I remove the gas block from the gun. Once I get 1000rds on the gun without cleaning, I'll 620 loctite the gas block on and pin it.
In theory I could have a bore'd grub screw in several port sizes and swap them out as necessary. You can buy a pack of 100 M5x0.8x4mm screws for something like $10. Could be a slick idea for a product. A gas block with interchangeable port sizes. But I thought I would pass the field expedient method along. Could be a cheap and relatively easy solution to fine tune a gas port for someone using parts they already have.
This morning I grabbed another cheapo lo profile gas block to try it on. The gas tube was frozen in the block and this block had a closed front end. I drilled a small hole in the front, right where the gas tube was. This allowed me to tap the tube out with a small punch. Then I gave the block the same treatment but I didn't drill the port out as I don't know what I'll need. It already has the cross pin hole drilled for a pin install. When I do install it one day on whatever future build I'll green loctite it to the barrel, and red loctite the gas tube end to prevent gas from shooting out. I'm developing a preference for "hard use" 'ish gas block configurations. This little gas port trick is a nifty technique that bypasses more expensive adjustable gas blocks that eventually seize from carbon but still have potential faults with springs, ball detents, and flat springs. And it frees you up from buying from unreliable companies like Black River Tactical. You can do this with any cheap gas block.
