Sun Devil MFG Adjustable Gas Key

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Sun Devil Manufacturing released their new Adjustable Gas Key at the 2015 SHOT Show. Dubbed the ADIGS (adjustable drop in gas system), their new gas key is compatible with both AR15 and AR10 bolt carriers. It’s adjusted via a self locking adjustment screw and is available in both a retrofit kit or already installed on one of Sun Devil MFG’s bolt carriers. Sun Devil MFG claims their new ADIGS helps reduce felt recoil and muzzle climb as well as help solve over gassing and cycling issues. The ADIGS kit retails for $59.95 over at Sundevilmfg.com.

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Ray I.

Long time gun enthusiast, archery noob, Mazda fan, Sci-Fi nerd, Whiskey drinker, online marketer and blogger. My daily firearms musings can be found over at my gun blog ArmoryBlog.com and Instagram.

Shoot me an email at ray.i@staff.thefirearmblog.com


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  • James

    Looks like another solution in search of a problem.

    • JumpIf NotZero

      A pretty clear statement that you don’t shoot suppressed, AND/OR, can not tell the difference between a properly gasses gun or not.

      • lucusloc

        So how does this prevent over gassing? The excess gas is still being tapped and vented to the BCG. All this does is prevent some of that gas from entering the BCG, and forcing it to instead act on the key itself.

  • Andrew Hobby

    Does this have “infinite ajustability”? Unless it has INFINITE adjustability I just can’t put it on my ultimate Tactical Operator Rig.

    Now where did I put my 45 degree sights?

  • J

    now what happens if you completely close it off?
    will it turn into a true DI system?

    • JumpIf NotZero

      The action won’t cycle at all.

    • Rob

      Yeah, this seems odd. They aren’t reducing the gas coming back from the front gas block. So if you close the screw all of the way, you still have a lot of pressure pushing on the closed gas key. It will tend to open the bolt carrier the same way that pulling on the charging handle would. The excess gas will escape into the receiver instead of most of it venting out of the bolt carrier vent holes. Not convinced it will work as advertised.

      • Christopher Armour

        Exactly, what problem is this product trying to solve? Overgassing? Nope, all the gas will still dump right into the upper no matter how you set the key. This product just might increase the likelihood of the bolt unlocking earlier than desired if too much pressure builds up on the set screw. The point of adjustable gas blocks is to adjust how much gas can even make it to the BCG.

        • FightFireJay

          Seems like it would increase wear and tear on the bolt lugs and barrel extention because the gas inside the BCG pushes bolt forward allowing less friction for the unlocking process.

      • lucusloc

        I too question the validity of regulating gas in this manner.

      • JumpIf NotZero

        “It will tend to open the bolt carrier the same way that pulling on the charging handle would.”

        Not even a little bit. But thank you for claiming you understand how DI in the AR-15 works while not actually having the slightest grasp of how the not-exactly DI system works.

        WOW, I can’t believe how many people ALSO don’t get this. I’m stunned.

        • Christopher Armour

          Really, well enlighten all of us ignorant enthusiasts. If this new wonder key was closed off completely, explain what you think would happen when a round is fired.

          • JumpIf NotZero

            Well, since I’ve done exactly that; pretty much nothing.

            OMG amazement that the AR15 isn’t 100% truely direct impingement! Call everybody!!!

            It’s almost as if the size of the expansion chamber and the shape of the bolt tail aren’t just arbitrarily designed. It’s almost (ALMOST) as if they “do” something.

          • Christopher Armour

            I understand how the expansion chamber uses the expanding gases to push the carrier back and unlock the bolt. But I’ve seen them at the very least short stroke with blocked keys. You’re saying you got zero movement on your BCG with a fully blocked key? The only way I can imagine that happening is on a very tight rifle.

        • DisqusIsBroken

          I’m pretty sure that you’re the one who doesn’t get it here.

        • Rob

          With the gas key completely closed the AR-15 gas system would be quite similar to the MAS-49. Without access to the expansion chamber the system will operate as a true DI. The gas volume maybe insufficient to completely cycle the action, but pressure in the gas key puts the same force into the bolt carrier as pulling on the charging handle. I suggest taking a Physics course, and losing the juvenile condescension.

          The expanding gas in the AR-15 both pushes the bolt forward and pushes the bolt carrier rearward prior to venting. But as all of the piston-operated version demonstrate, the system works just fine if you simply apply a reward force on the bolt carrier. Does that pass for a slightest glimpse?

          • JumpIf NotZero

            Without access to the expansion chamber the system will operate as a true DI.

            Except that it doesn’t.

            Perhaps you should ask Sun Devil what happens when you turn the screw completely off yea?

          • Rob

            As I said before the gas pressure into the gas key may not be sufficient to cycle the action normally, Force on the bolt carrier is a result of the gas pressure acting over a certain area. Essentially hydraulics. The cross sectional area of the gas tube is less than the surface area at the base of the bolt carrier, and the force exerted will be proportional to the difference in the areas. I don’t have measurements, but I would estimate the areas are maybe 10 to 1. So there is only 10% of the normal force present to open the action. This is more than “not even a little bit”, but how far back this moves the bolt carrier is hard to estimate. The force keeping the bolt carrier forward is the action spring, and the force is governed by Hook’s Law. The spring force is the least with the bolt carrier forward and grows as the spring compresses. So 10% of the normal force that would move the carrier all of the way back should move the bolt carrier more than 10% of the full distance. It is very difficult to observe bolt carrier movement with the naked eye. I would bet that it is opening slightly and then reclosing before you can see it. Run a piece of tape across the bolt carrier and the lower and see if it comes loose when you fire it.

          • raz-0

            Please tell me where this “extra” fouling will come from? Does the gas key magically put more powder in the cartridge to make more carbon? No. It miught move around where it comes from, but seeing that the inside of the carrier/bolt acting as a gas piston is where the fouling is nastiest, I’d suspect it is moving it away from there to areas that are already getting plenty dirty. If suppressed guns can run reliably, I’d say it’s all rearranging deck chairs within the margin of operation of the platform.

            That being said, sun devil and rubber city armory both have adjustable gas key products, and another company introduced a BCG with a switchblock type of gas adjustment for suppressed use.

            Both the sun devil and RCA keys are primarily intended for use on lightened bolt carrier groups. They are useful if you are stuck with permanently attached muzzle devices, or if you are rocking really long hand guards and don’t want to mess with super long allen wrenches, or cut holes in the side of your hand guards. Jury is still out on long term durability, but they do work very much like adjustable gas blocks as far as net effect.

            Similarly, I wouldn’t really consider them something you need for a standard mil-spec set up with decent sized gas ports.

          • Rob

            It is my understanding that a majority of the gas ported into the bolt carrier is vented out of the holes in the bolt carrier side when the bolt opens. If some, or all of the gas in the gas tube, is prevented from reaching the bolt carrier it cannot vent via the vent holes. This excess gas in the gas tube would then have to vent either back through the gas tube into the barrel after the bullet exits, or into the action. The hole back into the barrel is much smaller that the gas tube diameter into the action, so I would expect most of this excess gas to vent into the action.

            I am sure that there is always excess gas in the gas tube, and this effect only adds to it. How much of a difference it makes is hard to say. I am fairly certain that it will be dirtier than a system that regulates the gas at the source instead of at the destination.

            This product is probably useful for those who do not want to replace their gas block, and aren’t going to need to throttle the gas volume very much. I still think that it is solving the problem at the wrong end.

          • raz-0

            I don’t disagree with your understanding. I just think that dumping gunk in the upper in a general way is not really that big a deal in terms of functionality. Suppressors will do it, really effective comps will do it, and they don’t even cause less gas to foul up the bolt carrier internally. Also, it’s a niche product designed for gamey setups or specifics needs, The RCA, sun-devil, and gemtech offerings in this area are not sold or advertised as generally increasing reliability. They’re to fill specific needs.

    • Roy

      The bolt uses the gas going through that to unlock the action.

  • guest

    I like the option to have adjustable gas settings (cans, different ammo etc), but THIS specific solution is as half-a**ed as many others that rely on a screw without any means of locking it:
    It will either require some permanent thread locking compound that is not easely loosened (like ceramic compound), will not be easely adjustable after locking, and requires tools (!!!) for adjustment.

    Now look at Noveske’s adjustable gas block: very simple, very reliable, no tools needed, no compound, readily adjustable in the field.

    Oh and as far as such flimsy one-bolt solutions go: I had a Mini-14 gas block with a screw and a spring “holding” it in place. If memory serves me right it was made by ASI. After about 40 rounds the crew was blown out and never seen again. And I guarantee that someone will have this little screw shoot out into the lower receiver and cause all kinds of mayhem.

    • JumpIf NotZero

      Lol, no tools needed on the Noveske Switchblock? That’s funny. I’ve always needed a tool on mine, 1/2 because they seize up and 1/2 because of the heat. You also need a correctly length rail, and they aren’t cheap.

      This does not fill the same role as a switchable block. This is for tuning a gas system.

      • guest

        True, but at least you do not need to field strip the rifle.
        As for correct length rails – cry me a river. They have blocks with tubes of ALL lengths. I have mine (carbine) “inside” of a polylithic upper, which I dremeled out to fit. No issue.

  • Ethan

    Yep… that cutaway demo part is definitely colored with red sharpie.
    Been there, done that.

  • Wolfgar

    It is another option for tuning an over sized barrel port or ammunition. I love my SLR gas blocks, the screw will not back out, seize up and is adjusted by a simple allen wrench that they provide. This adjustable gas key is a less expensive alternative which doesn’t require the removal of the gas block. The more options the better:)

  • Rogier Velting

    Simple but (probably) effective… I like it. And anything that can further tune performance of a weapon is good, might even help improve accuracy a bit if done well.

  • Marc

    Adjustable gas is good. This is an option when adjustable gas blocks aren’t, otherwise I’d rather adjust the gas via the block.

  • Seems like a really bad idea to me. Take a gun that’s running fine, put this in and futz around with it and now your gun isn’t running so great anymore. Screw this. I want to simplify my gun, not add in more factors that could lead to failure.

    • JumpIf NotZero

      Cool story. I’ll let you know when I see an off the shelf gun that isn’t overgassed when suppressed. Oh, wait, that has never happened actually. hmm

      • So, I guess adjusting it with a switch at the Gas Block is too old fashioned… BEEN THERE, DONE THAT. Let’s make an adjustable Internal Part. Great idea. No… I’m well aware of supressor issues… and this idea is just a way to add more issues.

  • Shane

    Another solution in search of a problem.

  • your mom

    Hey JumpIF, you’re moron and a shill. It’s a stupid idea, as dumb as Gemtech’s new adjustable bcg. By stopping or restricting gas flow anywhere downstream of the gasblock, you are going to force more dirty gas into the upper receiver in and around the top and front of the bcg in the barrel extension region. OBVIOUSLY500 rounds with maybe 2 adjustments. When adjusting it, I use the tip of a round into the recessed switchblock button (which is made for a bullet tip) and just depress and rotate. Works perfect. The “off” position is true off, makes for a really quiet single shot suppressed with no bolt movement and no gas flow/fouling. You may have to mortar the gun a little to get the bcg loose if you turn the gas off and it’s really dirty…

  • lucusloc

    I know how the gas works in the bolt, the issue is you are still putting excess energy into the system. My question was how well this particular device would fix that problem, since it seems that the best solution would be to not allow the excess energy into the system in the first place (buy reducing the gas you port from the barrel).

    As others have pointed out above, We know that venting gas into the bolt is not necessary, since no piston driven AR does that, and they still work fine. (Yes, having the gas work in the bolt will get you more efficiency with the tapped gas, helping open your bolt faster than just having the gas work on the key.) The excess gas is still going to have an effect on the gas key, causing it to drive the bolt backwards. That is just how physics works. I have my doubts about how well this will help a truly over gassed rifle, or why we should replace varying the gas at the block with it.

    Could this actually work to slow the rifle down? I suppose so, buy virtue of making the gas you vent to the BCG less efficient (most of it will act directly on the key, not on the bolt itself), but that strikes me as “solving” the problem on the wrong end. Without actually knowing how much efficiency you gain by having the gas work in the BCG as opposed to on the BCG I cannot say if this will actually fix an over gassed rifle.

    A properly gassed rifle should short-stroke with a blocked key, I would not be surprised if you could make an over gassed rifle work just fine with a blocked key, but I have never tried it myself.

    • JumpIf NotZero

      but I have never tried it myself.

      Redundant when considered with all the text above it 🙂

      You guys need to take a step back and realize that this product WOULD NOT WORK if the gun ran “almost” on pressure on the key. It doesn’t.

      • lucusloc

        Given the existence of piston driven ARs, what exactly are we missing? The gun industry is famous for producing dubious and marginally effective products, as well as products that are complete and total BS. Most people here are trying to figure out weather this product fits into either of those categories. I have half a mind to run a test myself with an adjustable block set to wide open and see how far a blocked key will push the BCG back.