Maybe one of you here is a bit more knowledgeable on the topic.

Is there any advantage as far as the gas restrictions by utilizing one vs. the other? Eg. The gas being restricted up at the gas port on the barrel vs. right before it enters the carrier?

Topic came up today at the shop and I can't seem to really think if one is superior than the other.

I'm not looking for thoughts like needing to remove a rail to adjust the gas or removing the carrier if its on the gas key itself. Just strictly looking for thoughts regarding the gas flow.

Thanks!

Gas pressure is gas pressure: the bolt/carrier doesn't know where it's regulated.

That's kind of what I figured. Just wasn't sure if there was any knowledge out there that one had advantages over the other in terms of regulating gas or if its all the same.

If shooting suppressed, wouldn't the adjustable key leave you with just as much blowback as before?

Just a thought - not sure if you're shooting with a can.

If you're adjusting at the block, then the amount of gas allowed into the tube is going to be constricted.  If you're adjusting at the key, then the excess gas that has been bled off the barrel is still going to be dumped into the upper.

From the individuals I've spoke to who manufacture them, they say the excess gas is vented forward, through the "clover leaf" where the gas tube enters the upper receiver.

With an adjustable key, why is there any gas "bled off" into the upper?  Isn't it just an adjustable restriction, just like an adjustable block?
Restricting the gas tube at one end vs. the other?

I have to admit, I'm skeptical of that, but I have no hands on experience with the adjustable keys, I'm just working off of broad concepts.  

Wouldn't redirecting the excess gas forward require the bolt to stay locked artificially longer?  Once the BCG starts moving rearward, the gas isn't going to make a 180 on its own.

Regardless, though, why allow stuff into the gas tube if you don't want it in the upper?

It's still more dirty gas being blown in to the upper receiver. If you restrict the gas at the gas block you have a smaller amount entering the upper receiver.

Also do you really think the manufacturer of said adjustable gas key would talk about a draw back to the product they are trying to sell you?

I'm not convinced there's anything more than a negligible difference in the gas volume and fouling coming from the gas tube with either method in question here.  A large portion of the fouling that you see in the receivers comes back through the bore/chamber.  A reduction in fouling is seen after restricting gas flow to the carrier because it slows the action and delays the unlock of the bolt, allowing the pressure in the bore to drop substantially before it's open to the receiver via the chamber.  So, an adjustable gas key can do basically the same thing as an adjustable gas block if my thinking is correct.

I readily admit, that's a big 'if'.  I've tried a lot of different gas adjustment/restriction solutions, but I've yet to try an adjustable key.  I do plan to try one though and I personally don't expect to notice any more fouling in the receivers than a configuration where the gas is restricted at the gas block.

Yes, but the tube would have a "full charge" in it all the way to the key. Now would that slow the gas from coming down the tube after it hits the bottle neck in the key? I have no idea. We're talking a very short time period here.




Good question. I don't know the answer. I guess if anything it would just slow the bolt from unlocking. You're correct when you say the gas itself won't turn 180 degrees and vent out on its own. I guess I was picturing the gas hitting the key and directing back forward after the key came off the tube.




As the other poster stated, a lot of that comes from the bore itself. To answer your second question, yes. I manage an FFL and have a very good relationship with this particular company. We openly talk about stuff all the time.

Furthermore, the guy I spoke to flat out said, his thought and reason pursuing the adjustable gas key vs. gas block was that if there was an issue with the gas regulation you could just flip a regular BCG in there and you were good to go. He didn't state that he thought one was better than the other but suggested that perhaps the ability to quickly solve any gas issues that may arise vs. having to remove a hand guard to potentially play with it was an advantage. He also noted that the upper receiver was not as dirty as some of you were suggesting it would get.

I was just wondering if anyone had any practical knowledge as to if one system were better than another or if at the end of the day it was all the same as the gas entering the carrier group was getting restricted, one way or another.

FWIW, I think every solution to regulating the gas feed has pros and cons and no solution is the 'best' in all situations.  It's not that readily apparent what all those pros and cons are, and IMHO there are some big assumptions made about what's really happening with each solution (including by me).  

In the case of the adjustable carrier key, a big advantage to me is that it offers a solution for a situation where changing gas blocks, receivers (such as the W.A.R.), or other parts just isn't a possibility.  I like my LMT MRP uppers, but options are very limited for regulating gas on those.  I've been using a combination of the LMT enhanced carrier along with really heavy buffers to delay the bolt unlocking and lessen felt recoil, but still not quite happy when it comes to suppressed use.  The adjustable gas key would be an easy and relatively cheap way to regulate gas feed in one of those uppers to get it where I want it with a suppressor.

I've used both, and both work.

With a suppressor, most of the "gas face" is still what comes out of the chamber.
If you can slow extraction with either method, you're going to reduce that.

I put a RCA adjustable key on my .308, and it made a noticeable difference in recoil by slowing down the bolt.

I tuned it to just cycle/lock on my lightest loads unsuppressed, and it runs like a top with anything.
Before I was getting heavy extractor marks suppressed, and the brass was slamming off the rear of the ejection port, now it's a lot smoother and the brass will last longer.

My experience is only with standard DI systems and an RCA adjustable gas key.  I don't notice any difference in the amount of fouling produced by one system vs the other.  Like the others, the amount of fouling I see in the chamber is roughly equal to the degree of fouling on the bolt and carrier.  As for the questions about excess gas in the gas tube, I suspect that is a non issue since we are dealing with gasses (Boyle's Law, etc.), not solid objects with substantial mass and momentum.  

If you carefully consider what is happening in slow motion with an adjustable gas key, the bullet passes the port, gas enters the tube at high pressure, the carrier with its key begins to move with the tube still inside the key.  By the time the cam pin engages the bolt and begins to unlock it, the bullet has left the barrel and pressure has begun to drop.  During this interval, some gas has leaked around the head of the tube and out the mouth of the gas key, admittedly more than if pressure had been restricted at the block, but still not that much gas compared to the volume vented inside the carrier.  By the time the reciprocating carrier and its gas key clears the end of the gas tube, pressure (beyond atmospheric) has presumably dropped to near zero.  Any remaining gas in the tube simply comes to rest since the high pressure is gone, it does not have enough mass to continue jetting out the end of the tube.

Once you have tried adjustable gas, its advantages are obvious.  However, the net difference on fouling of either approach (block or key) should be negligible.  - CW

I'm quite curious to see how the adjustable gas keys hold up over time. I'd love to have the capability, but I find myself tending to prefer rifles with a FSB. I worry about the reliability of sticking a screw in the back of the gas key, to be blunt about it.

This is just a theory of mine, but wouldn't the set screw in an adjustable gas key hold up longer than the screw in an adjustable gas block since the gas is a lot cooler at the carrier than at the barrel?

Curious as to the round count that produced that....also, whether suppressed or un-.  Mine has less than 200 rounds since install, but have noticed nothing like yours.

Are you using the Gemtech BCG that they are supposed to be releasing soon?

Cool. I hate to sound like I'm talking bad about Gemtech, because I like their products/them as a company,  but I'd rather have internal components of my rifle come from you guys based on the quality of the parts I've seen you turn out.

Isn't there an adjustable gas tube as well?

Will you offer an adjustable standard weight carrier also?

That is cool.  I have GOT to try one with the can.  Is there a standard weight carrier?

You're killing me.