So, I'm not a gunsmith, but I like to tinker. Once I got a suppressor, I discovered my brass was covered in soot and the action got very dirty very quickly. I considered buying an adjustable gas block, but the prices seemed high for what you were getting. It seemed simple to drill a hole, tap it, and install a set screw or two. A little internet research and I discovered that's exactly what others are doing to achieve the same effect. I'm no machinist, so I didn't get too fancy.
I started by removing the rail, gas block, and gas tube. I eyeballed a spot on the side of the gas block that seemed to be right in the middle of the gas tube opening and the barrel opening and in line with the gas port. Used a center punch and then drilled through to the gas channel. Then tapped for a 4-40 screw. Ideally, you should use a bottom tap for this. If you use a regular centering tap, you wont get threads cut deep enough. I used a centering tap with the end ground off. I started with this tiny screw because I could go a little bigger but not much and did not want to overdo it. This long screw was the only screw I had and I jam nutted it to hold it in place for testing. Reassembled the gas system but no handguard and test fired.
I know it's hideous, but it was just a proof of concept. But it didn't work. I still had last shot hold open without the suppressor which tells me A) the gun is crazy overgassed and B) I needed a bigger screw.
So I disassembled again, but left the gas tube connected to the gas block this time, as the roll pin is a pain to remove and replace and I didn't need to do it. This time, I drilled out and tapped for a 6-32 screw. Seeing as how the first time I tapped it, I ran the tap all the way in and the screw was kind of loose, I didn't bottom out the tap this time. I test fit the screw and it would barely start to thread in, so I tapped it a little more. This time the screw was snug and after I gently worked it in, it threaded in fully and I don't think it's going to move so a second screw from end, or a jam nut will not be needed.
I test fired with the screw fully turned in, and no suppressor. Voila! No last shot hold open! A couple more single rounds confirmed. I turned the screw out 1 turn and fired a couple single rounds. 2 of 3 held the bolt open. One half turn more and I called that the baseline for unsuppressed. With the suppressor attached, I turned the screw all the way in. I had last shot hold open every time. I had hoped I could turn the gas down more, but this is definitely an improvement. I am noticing less soot on the cases, the action seems to be cleaner, I am getting less gas from the ejection port, and the recoil is significantly less.
Here you can see the gas adjustment screw is accessible through the rail after it is installed. I plan to tweak this a little more to see if I can restrict the gas a little more, but to me, at least, it is an acceptable alternative to paying $75 or more for an adjustable gas block. I also realize there are many different ways to accomplish this same task and mine is very rudimentary, but it is a starting point. The next logical step would be to increase the size of the screw to 8-32 to further block the gas, but I don't think there is enough room. The thickness of the gas block between the barrel and the gas tube is only .165" and an 8-32 screw has a thread diameter of .164" so if I was off by just a tiny bit, I could hit the barrel or the gas tube. Maybe it would work, but I didn't want to chance it.
What say you all? Worth it? Terrible idea?
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Originally Posted by adcoch1
