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What's involved with making a gas block adjustable?

challenger

Stainless
Joined
Mar 6, 2003
Location
Hampstead, NC-S.E. Coast
I am looking to make my AR gas blocks adjustable. I've read of people drilling & tapping for a set screw but I don't see how this will help adjust the gas pressure. What am I missing?
Thanks
 
I put one like one of these on my service rifle after rules changed to allow scopes and I ditched the sight block. It works great. Infinite adjustment. I have a pet load for 600 yd. and I just screw it shut, then open it about half a turn each shot until it cycles, then go 1/2 more and lock it down.


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An adjustable gas block does not alter gas pressure. Rather, it restricts gas FLOW.
It amounts to the same thing though. ;-)

Think of a taper tip projecting into the flow ports as the gas makes the 90 degree turn inside the block. Some military versions sport a multi position lever providing fixed restrictions at each setting.
 
I put one like one of these on my service rifle after rules changed to allow scopes and I ditched the sight block. It works great. Infinite adjustment. I have a pet load for 600 yd. and I just screw it shut, then open it about half a turn each shot until it cycles, then go 1/2 more and lock it down.

I do the same but use the JP adjustable A2

Works great and the JP sight is nice gear.

 
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I am looking to make my AR gas blocks adjustable. I've read of people drilling & tapping for a set screw but I don't see how this will help adjust the gas pressure. What am I missing?
Thanks
You really can't understand how a restriction in the gas path, can change how the gun cycles? Or did you think the set screw was to hold the gas tube in place?

Restrict the Flow/Pressure acting on the carrier or piston, and you restrict how hard you beat the piss out of the buffer or receiver. And yourself, in some cases. Per above, close it until the action will not cycle, open it until it will, reliably, plus a little bit to make up for losses from fouling accumulation, if you are not going to have the screw set up with a hand operable control on it of some kind (Knob, lever, etc).
 
You really can't understand how a restriction in the gas path, can change how the gun cycles? Or did you think the set screw was to hold the gas tube in place?

Restrict the Flow/Pressure acting on the carrier or piston, and you restrict how hard you beat the piss out of the buffer or receiver. And yourself, in some cases. Per above, close it until the action will not cycle, open it until it will, reliably, plus a little bit to make up for losses from fouling accumulation, if you are not going to have the screw set up with a hand operable control on it of some kind (Knob, lever, etc).
Sorry I'm such a dumbass.
I thought the screw adjusted bleed off and not simply restriction.
It seems, to me, that an adjustable block is a really good modification especially for reloads snd, "non standard", loads.
 
If you have a hold open device the standard way to set a gas regulator is to load a single round in the mag and adjust till the bolt stays back this ensures a full bolt stroke. You can give it little more to ensure reliability.
 
It needs to be more than a set screw, Should have a tapered Stem and seat. It is a very nice thing to have. 50 years ago I had an FN model 1949. It was 7X57 and it had such an adjustment. Open it to much and it could rip off a piece of the rim and throw the case 20 feet or more. Tune it in and the case falls at your feet and that excess energy goes behind the bullet.
 
You really can't understand how a restriction in the gas path, can change how the gun cycles? Or did you think the set screw was to hold the gas tube in place?

Restrict the Flow/Pressure acting on the carrier or piston, and you restrict how hard you beat the piss out of the buffer or receiver. And yourself, in some cases. Per above, close it until the action will not cycle, open it until it will, reliably, plus a little bit to make up for losses from fouling accumulation, if you are not going to have the screw set up with a hand operable control on it of some kind (Knob, lever, etc).
Flow and pressure are not the same thing. The gasblock is a basic needle valve, it adjust the flow rate (the volume of fluid ) able to pass through it... the pressure remains constant. The greater the flow, the faster down stream volume reaches pressure equalibrium performing a cycle of the action. For example If you are trying to use subsonic ammo, but your gun keeps jamming each cyle, you must determine if the cause is one of two things..... cycle time or insufficient pressure.
1) determine the minimum pressure and time is requried to ssuccessfully complete a cycle of the action of your firearm.
2) determine what gad pressure the subsonic ammo produces

If the gas pressure produced is equal too or greater than the min pressure required to cycle the action, then an adjustable gas block will correct the problem by adjusting the cycle time. BUT.... if the issue is caused by insufficient pressure produced by the ammo, then adjusting the gas block will not help, ie the firearm requires say 50 psi to perform a cycle but the ammo only produces 45 psi then no amount flow adjustment will help. To correct a low pressure problem you would instead need to replae the buffer with one that has a lower pressure spring.

So whether or not an adjustable block is worth it is determined by the circumstance.
 
I put one like one of these on my service rifle after rules changed to allow scopes and I ditched the sight block. It works great. Infinite adjustment. I have a pet load for 600 yd. and I just screw it shut, then open it about half a turn each shot until it cycles, then go 1/2 more and lock it down.


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I went Distinguished and HM with a standard a2 front sight and continued with a non adjustable low profile gas block after, never saw the need for restricting gas in an AR or adjusting Dwell timing like the old m14/garands did as theres no moving parts on the front of an AR gas system. Just another thing to break/fail in the middle of rapid fire lol.
I used to take old shot out service rifle barrels and cut them down to carbine length gas systems for blaster Ar's and would time the old gas port to use. THe gas port for a rifle is way bigger than needed for a carbine but i ran it anyway with the plans to drill and tap a set screw in the old port then drill it to proper size. Never needed to as the gun seemed to function just fine. Overgassed is not nearly as much of a problem as undergassed.
That said when making lightweight service rifle barrels for kids (think actual a2 under the handguard profile) from shot out WOA long gas system barrels I did need to drill and tap the gas port and put in the right gas port size as the guns would eject brass two shooters over, so there is a limit
 








 
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