They just dropped this today. Pretty cool. Specifically the part where you can swap out manifolds and drill your own ports in the manifold plates. I've been drilling and tapping the gas ports in fixed gas blocks and using the grub screws as manifolds, by drilling them out with fine #48 or #52 bits. This allows for two settings and offers manifolds with pre-drilled 0.034" holes for you to open up. Complete customization for a dual rifle setting
Griffin two position adjustable gas block
- Thread starter JR1200W3
- Start date
Interesting concept, but I wonder how good of a seal you can get between the adjustment manifold and the body of the gas block. Someone used to make a similar design, but the manifold slid back and forth perpendicular to the bore axis. It was a leaker.
I sat through most of this video before I had to cook dinner, but I like what I see. I’m probably going to wait in some reviews but this might be purchased for a 12.5 SBR I’m piecing together.
I just put together a 12.5" pistol. The barrel came with a .080" gas port on a hybrid length gas. It was violent, hard recoiling, and loud as shit with a suppressor. I drilled a set screw out to .070" and then again to .067" and installed it in the gas block. It runs well suppressed with a 67 thou port.
Here is my variation of that mod. Most set-screw gas blocks use 10-32 set-screws. The drill size for a 10-32 tap is a #21, or 0.159", and some manufacturers drill the gas block passage connecting the gas port to the gas tube at the same time and with the same drill as when they do the set-screw hole. If the gas block is like that, you only need to tap the gas passage, use a ported 10-32 screw, and then you can still use the rear set-screw. Plug or bottom taps work well, as you can tap to a depth where the ported set-screw bottoms out just short of the gas tube bore. If the gas passage is smaller than 0.159", like 0.125" which is also common, you can open the passage up with a #21 through the set-screw hole, then continue.
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I used one of those little screw thread pitch identifiers and came up with M5x.08 for the grub screws. Must be super close to 10-32. I used the grub screw that came out of that rear threaded hole. But I couldn't get the same sized tap through the threaded hole so I had to open it up to .220. I'm sure I could tap that new hole and order a larger pointed grub screw from McMaster Carr but I kinda think grub screws on gas blocks are a little insane. For non-precision ARs, I just use a little red loctite on the journal and pin the block to the barrel.
ETA, how were you able to tap through the rear hole without opening it? Skinny shanked tap?
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Even some of these port sizes are ginormous. I use .070" on 13.9 and 14.5 mid gas with high back pressure cans, milspec BCGs, and A5H2's. Runs unsuppressed and suppressed. I can't imagine a 96 thou. I've heard there's a slight difference in sizes barrel ports vs gas tube ports(in the case of BRT EZ tune tubes) to generate the equivalent pressure in the gas tube. I opted for the predilled .034" plates and I have a collection of small bits in 67, 70, 73, and 76 I can use to open them up.
Most 10-32 taps aren't long enough to reach through the gas block to tap the interior hole without the tap shank running into the exterior hole.
Ya, I bought one of those and it's still hanging on my wall. I think they have .067 port. It's dirt cheap at $20 but it would be nice if it would already be drilled for a dowel pin. Using the grub screws as hole plugs or manifolds just allows you to use gas blocks you already have instead of having to buy more or worse, dealing with Black River Tactical.
.063"
You need the major diameter of the grub screw to be smaller than .156" unless you plan on buying a custom tap or custom grinding an existing tap.
I bought my tap and vented set screws from Mcmaster car. Take a grinder and remove the rear threads on the tap so it clears the bottom hole as you thread the top. I also rounded the tap point to allow me to get deeper through the hole. Now the shortest setscrews will thread all the way up and into the gastube to keep from having to grind them smooth with the inside of the gasblock.
