Posted: 7/28/2013 2:00:22 PM EST
MicroMOA notified me that they now have 3 position "blank" gas plates in stock, so I ordered their adjustable gas block with the 3 position blank (1 dimpled "off" position and 2 positions with small pilot holes drilled). My thought was: 1 position for off, 1 position for suppressed subsonic, and 1 position for supersonic not suppressed. It was promptly shipped and included 2 3-position blank plates.
The gas block was easy to install, but removing the gas plate for drilling was impossible until I removed its spring. It easily fit under my Samson Evolution handguard, but the holes in the handguard were too small to insert a bullet tip to move the gas plate, so I simply used a small screwdriver to move the plate. Since I would probably would removing the plate so many times as I gradually opened up the hole for gas, during testing I simply omitted the spring and held the gas plate detent pin in place with a bent plastic straw.
I borrowed a numbered drill bit set and would open up one of the pilot holes one drill bit size at a time, firing my 220gr suppressed subsonic loads and unsuppressed supersonic loads to see what happens. My bbl is a chrome lined, PSA 8" 300 blackout bbl. I had a Gemtech Vortex Quickmount on the muzzle, and when suppressed, was using a Gemtech Quicksand suppressor. Measurements were taken with my Lyman calipers. On the 11th drill bit opening (.087") it fired flawlessly with subsonic suppressed and supersonic not suppressed, locking the bolt back when the magazine was empty. I then properly put it back together using its spring and took it for further test firing today. 45 rounds of subsonic suppressed and supersonic not suppressed later, the functioning was still flawless.
Interesting in that with my rifle and my reloads I ended up with 1 setting for subsonic suppressed and supersonic not suppressed. I used to have another maker's adjustable gas block on this bbl and found it also used the same setting for subsonic suppressed and supersonic not suppressed, BUT WHEN THE GAS WAS "TURNED OFF" IT STILL LET SOME GAS THROUGH. I have times I want the gas completely turned off for the utmost in quiet using manually cycled very light loads, thus I bought the MicroMOA gas block system. I have yet another maker's adjustable gas block on a third upper that uses different settings for my various loads, suppressed and not. So your results may vary with your setup. I may use the 2nd pilot hole for supersonic suppressed. When I first started opening the pilot hole I did some shots supersonic suppressed as an indicator that I was getting close to letting enough gas through for subsonic suppressed and supersonic not suppressed. With supersonic suppressed, an opening of .069" gave proper functioning. Empties were ejecting in the 4 o'clock direction, so opening the gas hole 1 more drill bit size probably wouldn't hurt...might have to do that come colder weather.
I'm pleased with the performance and features of the MicroMOA adjustable gas block, and I still have another gas plate and an unused hole in my one plate to play with.