Adjustable gas key

[montana]

Adjustable gas keys have been around for awhile and I was wondering if anyone here has any experience with them and what their thoughts were with them ? They look like a good alternative to an adjustable gas block.

http://www.fourguysguns.com/articles/sundevil-adigs

[LRRPF52]

The advantage to this approach is that you no longer are choking the gas port, which is a factor in early port erosion on your barrel. We want gas to freely flow through the gas port into the tube, rather than hit a choke device in an adjustable gas block.

Critical to its functionality is going to be prevention of leakage in the rear of the key where the set screw is, and the continued ability to turn the set screw, which commonly is carbon welded in place on gas block systems.

I'll look into these myself and try one out. You want to degrease the carrier and key thoroughly before installing, which I would use acetone on heavily until it is bone dry. You also want to compression stake the Grade 8 fasteners with an appropriate tool.

[montana]

The advantage to this approach is that you no longer are choking the gas port, which is a factor in early port erosion on your barrel.

I have never heard about adjustable gas ports being a factor in early port erosion compared to non adjustable ports. If there is more information somewhere on this subject I would appreciate a link to it.

If the adjustable key is viable it would be a great alternative, "not to mention cheaper method" to controlling gas.

[LRRPF52]

Think about it. High pressure gas/plasma is expanding behind the projectile down the barrel, with enough force to spit a substantial little piece of metal out at anywhere between Mach 2 and Mach 3.

When that high pressure gas/plasma cloud passes your gas port, it follows the path of least resistance up through the port hole, into the gas block, then the tube.




With most of the gas systems, you are above 10ksi at the port. If we go ahead and introduce a choke, like a set screw or plate with smaller hole above the port, pressure will be contained in the port longer, which is why we get tuned reciprocating mass effects from an adjustable gas block.

With the pressure containment/choking in the gas port area, we will naturally see increased port erosion, with more need to dial down the gas.

The adjustable key eliminates this problem, which is why I kinda like the idea of it over a gas block. The main disadvantage is having to remove the BCG to make adjustments.

[Klem]

I have never heard of 'early throat erosion' being an issue with adjustable gas blocks either.

While the venturi effect in theory would place more pressure on the adjustable gas block one would hope the manufacturers have considered this and use the right metallurgy and components. If the block lasts as long as the barrel then that's good enough for me.

Seems to me there's little difference in an adjustable key or block; including disadvantages.

[montana]

Any gas operated firearm with a barrel port will suffer barrel erosion with use. My question is whether or not an adjustable gas block increases or doesn't increase barrel erosion compared to a standard gas block and if so is it even enough to be concerned.

Many manufactures over gas their rifles to obtain reliability with a variety of ammo. This can also have a negative effect on other operating functions of the rifle. The AK is notorious for this as are many AR rifles on the market. As the non adjustable gas block is used the gas port will erode more and more without any means of backing the gas down exacerbating the situation. If an adjustable gas block creates more barrel erosion than a non adjustable gas block how much more and is it enough to be a concern over the life of a barrel is the real question. Does using an adjustable gas block prematurely reduce accuracy life of a barrel compared to a non adjustable gas block and if yes how much? Do the benefits outweigh the negatives, does it matter in multi gun or could it be a concern with precision shooting? This would be a good experiment if it is thought to be a real concern.

[Klem]

I hear you, and fair questions, but also a fair amount of effort and ammo by someone to figure all this out.

My a priori theory is there is so little difference in barrel wear between adjustable blocks and non-adjustable blocks as to it not being a valid criterion in block choice.

If restricting the flow at the gas block increases the pressure in the barrel then it will always be still below that of a normal bolt gun with no gas system. And those barrels seem to last just as long as AR barrels that are not abused (i.e. no auto mag dumps).

[Lonehill]

I don't think the average person will ever shoot their rifle enough for this to be a problem. Would think the barrel would be shot out before this is an issue.