AR Pistol Gas Block

[CTBay]

I need to sell a couple of my late fathers guns to cover a couple expenses he left for my mother. He had an AR pistol which isn’t my thing. I like aiming, not pointing.
Its 300 blackout and has an M-LOK hand guard. I have never shot it and before I offer for sale or auction I want to be sure its functional and safe. I took it out to shoot it and it won’t cycle another round in the chamber. Probably a problem with the gas block. So I disassembled the thing and sure enough the two screws at the bottom of the gas block are loose and it moved 1/4” forward so the holes don’t line up. I fully seat it and tighten the set screws. I try it again and it still won’t cycle.
So now I have the gas block completely off and I am noticing 2 additional adjustment set screws. One at the front and one on the side. What are these for? I blow in the tube and adjust the set screws only as far as they don’t restrict airflow. Now the stupid thing fouls on the hand guard.
I figured I would just replace this weird gas block with a typical basic one. I take the roll pin out to separate the gas tube from the block and its not coming out. Not sure why it was pinned. I am going to have to get a pistol length gas tube and replace both parts.
What is the deal with this fancy pants gas block? Why does it need all these adjustments with all these set screws? What are the adjustments for? I have put together 6 or so ARs so far and these is the first I have seen a gas block like this.

 

[I Love Bourbon]

I'm not familiar with that particular block but it's most likely adjustable for the amount of gas that is directed into the system. It can be tuned for specific ammunition etc.

 

[JEBland]

From a quick image search, looks like a Seekins Precision adjustable gas block: https://seekinsprecision.com/low-profile-adjustable-gas-block.html
As I understand it, one adjusts the gas, the other sets the place of the adjustment screw.

Haven't watched it through for myself, but here's a video from their YouTube channel.

 

[bcannon]

That's a Seekins gas block. The set screw on the side is to adjust the gas and the one in front is to lock down the adjustment screw IIRC. I'm not fully awake yet so I could be backwards and front screw could be adjustment and side screw lock down. I have a couple in my parts bin, I'll look and get back to you in a few.

 

[bcannon]

From a quick image search, looks like a Seekins Precision adjustable gas block: https://seekinsprecision.com/low-profile-adjustable-gas-block.html
As I understand it, one adjusts the gas, the other sets the place of the adjustment screw.

Haven't watched it through for myself, but here's a video from their YouTube channel.

^^^^ watch this instead, save me from digging around today..

 

[nucular]

And try to get that one figured out before you sell. Someone buying a 300 pistol will probably want an adjustable one especially if they shoot suppressed.

 

[CTBay]

It was suppressed. Not selling suppressor with it of course. Im going to check that video out after work.

Perhaps it would have cycled had I tried it with the suppressor to start.

Thanks everyone for your help!

 

[BigRed3588]

I need to sell a couple of my late fathers guns to cover a couple expenses he left for my mother. He had an AR pistol which isn’t my thing. I like aiming, not pointing.
Its 300 blackout and has an M-LOK hand guard. I have never shot it and before I offer for sale or auction I want to be sure its functional and safe. I took it out to shoot it and it won’t cycle another round in the chamber. Probably a problem with the gas block. So I disassembled the thing and sure enough the two screws at the bottom of the gas block are loose and it moved 1/4” forward so the holes don’t line up. I fully seat it and tighten the set screws. I try it again and it still won’t cycle.
So now I have the gas block completely off and I am noticing 2 additional adjustment set screws. One at the front and one on the side. What are these for? I blow in the tube and adjust the set screws only as far as they don’t restrict airflow. Now the stupid thing fouls on the hand guard.
I figured I would just replace this weird gas block with a typical basic one. I take the roll pin out to separate the gas tube from the block and its not coming out. Not sure why it was pinned. I am going to have to get a pistol length gas tube and replace both parts.
What is the deal with this fancy pants gas block? Why does it need all these adjustments with all these set screws? What are the adjustments for? I have put together 6 or so ARs so far and these is the first I have seen a gas block like this.

The video above is pretty straight forward and should solve your problem, but one part of your description caught my attention. I’ve had one adjustable block that fouled the handguard, but it was designed to bleed gas. It doesn’t appear the Seekins was designed to do that. If your adjustment screws are set, there’s probably an alignment issue with the gas tube.

 

[CTBay]

The video above is pretty straight forward and should solve your problem, but one part of your description caught my attention. I’ve had one adjustable block that fouled the handguard, but it was designed to bleed gas. It doesn’t appear the Seekins was designed to do that. If your adjustment screws are set, there’s probably an alignment issue with the gas tube.

The back of the MLOK nuts is what it was running into for all the stuff attached to the hand guard. So I took all the stuff off the hand guard.

There is really only one adjustment screw. The other adjustment screw is only to keep the first adjustment screw in place. Im blowing down the tube and adjusting the screw only as far as it begins to impede the air flow. Back it off a smidge and then set it with the front screw.

I try it again yesterday and it still doesn’t cycle. I cannot just shoot in my backyard. I have to ask a friend and plan ahead to test fire it. I left the hand guard off yesterday so I could adjust it right where I’m shooting it. Of course it wants to **** pour rain on me and I forgot my ears so I only got the one shot off.

Its shooting one round and ejecting the brass not very far and not chambering another round.

I also cleaned the tube to make sure it wasn’t gummed up with crap.

When I loosen the set screw any further out it extends outside of the gas block and runs into the hand guard. So I need to adjust it until it works, set it, and hopefully its not sticking so far out of the block it interferes with the hand guard. Its tight. There is very little room between the inside of the hand guard and the gas block. Not much room for any of the screws to be sticking out.

Its worked before, it will work again. Its missed the boat for the next auction with the other guns but oh well. I’ll fiddle with it Saturday.

 

[BigRed3588]

The back of the MLOK nuts is what it was running into for all the stuff attached to the hand guard. So I took all the stuff off the hand guard.

There is really only one adjustment screw. The other adjustment screw is only to keep the first adjustment screw in place. Im blowing down the tube and adjusting the screw only as far as it begins to impede the air flow. Back it off a smidge and then set it with the front screw.

I try it again yesterday and it still doesn’t cycle. I cannot just shoot in my backyard. I have to ask a friend and plan ahead to test fire it. I left the hand guard off yesterday so I could adjust it right where I’m shooting it. Of course it wants to **** pour rain on me and I forgot my ears so I only got the one shot off.

Its shooting one round and ejecting the brass not very far and not chambering another round.

I also cleaned the tube to make sure it wasn’t gummed up with crap.

When I loosen the set screw any further out it extends outside of the gas block and runs into the hand guard. So I need to adjust it until it works, set it, and hopefully its not sticking so far out of the block it interferes with the hand guard. Its tight. There is very little room between the inside of the hand guard and the gas block. Not much room for any of the screws to be sticking out.

Its worked before, it will work again. Its missed the boat for the next auction with the other guns but oh well. I’ll fiddle with it Saturday.

It sounds like you’re running it wide open, so cycling shouldn’t be an issue. Have you checked the gas key? A loose gas key will leak enough gas to cause the exact problem you’re describing. Throw a different BCG in it and see if you have the same problems.

If the gas key isn’t the issue, the block is leaking or it isn’t completely aligned with the barrel port. It sounds like you’re getting airflow through the tube and gas block, so just cover the hole on the block that aligns with the barrel port and blow into the tube. If air is moving, the block is leaking.

 

[CTBay]

It sounds like you’re running it wide open, so cycling shouldn’t be an issue. Have you checked the gas key? A loose gas key will leak enough gas to cause the exact problem you’re describing. Throw a different BCG in it and see if you have the same problems.

If the gas key isn’t the issue, the block is leaking or it isn’t completely aligned with the barrel port. It sounds like you’re getting airflow through the tube and gas block, so just cover the hole on the block that aligns with the barrel port and blow into the tube. If air is moving, the block is leaking.

I still haven’t got back to messing with it. Going to a military friends house Saturday. He is going to help me work it out.

You are probably right about the gas key. The AR pistol in question had a silver color (nickel boron maybe). I thought it was cool just because it was silver. I know from building my own 300B rifle that a 5.56 BCG is no different from a 300B BCG so I swapped the cool silver one into my rifle and put the black one I had in this one I am having trouble with. I planned to put the BCG that was in it back and see if that helps. The silver one also didn’t work very well in my rifle. It cycles but hangs every 3rd or 4th round. Its not extracting very far when it extracts at all. The gas key on that BCG must have been tuned for that gas block. Hadn’t mentioned that BCG swap but you nailed it.

It’s annoying when things don’t work but I am enjoying the education. Still working on getting added to the family trust so I can use the suppressors. Im interested in understanding how all these parts work together so I can get my rifles set up for suppressors.

 

[CTBay]

It sounds like you’re running it wide open, so cycling shouldn’t be an issue. Have you checked the gas key? A loose gas key will leak enough gas to cause the exact problem you’re describing. Throw a different BCG in it and see if you have the same problems…..

You were right. I put the nickel bolt back into the AR I was having trouble with. I noticed the gas key screws were loose. They also had been loose for sometime because there was residue all under it. I cleaned it and then put blue loctite on the screws as well as staking them again. It worked great after that. Problem solved. I still wanted to steal that nickel bolt carrier for my rifle. I tried to swap the whole BCG and it didn’t work. Ill bet I could tune the adjustable gas block to make it work. My friend said some guys drill the hole bigger to get more gas. Im not doing that. We tried swapping only the bolt carrier and not the bolt itself. Same problem.

Durkin tactical has nickel BCGs for $90, I can get what appears to be a really nice one for $150 at local shop. I’ll probably support the shop and get that one.


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[BigRed3588]

You were right. I put the nickel bolt back into the AR I was having trouble with. I noticed the gas key screws were loose. They also had been loose for sometime because there was residue all under it. I cleaned it and then put blue loctite on the screws as well as staking them again. It worked great after that. Problem solved. I still wanted to steal that nickel bolt carrier for my rifle. I tried to swap the whole BCG and it didn’t work. Ill bet I could tune the adjustable gas block to make it work. My friend said some guys drill the hole bigger to get more gas. Im not doing that. We tried swapping only the bolt carrier and not the bolt itself. Same problem.

Durkin tactical has nickel BCGs for $90, I can get what appears to be a really nice one for $150 at local shop. I’ll probably support the shop and get that one.


Sent from my iPhone using Tapatalk

I had a feeling it was the gas key. I had the same issue with a nickel BCG a little while back. It came from the factory with a loose key that hadn’t been staked properly. And here’s the best part…the manufacturer was FailZero. Nothing like dropping $235 on a BCG from a company that calls themselves FailZero and having to fix it out of the box smfh.