Adjustable gas block required for suppressed 18" 6.5G Larue UU kit?

Jul 11, 2010
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#1
After speaking with a friend who has a 243 LBC upper for his AR about the assembled Larue UU I ordered last week, he intimated that an AGB was going to be a must for running suppressed 100% of the time.

I use an AGB on my 12” .308 upper that’s run suppressed full-time, but haven’t seen the AGB ‘requirement’ mentioned here or on the 6.5G Forum for the 6.5G in general or the Larue UU upper specifically.

I’m having Larue leave the tranqilo brake off my upper as I’lm going to Rocksett an AAC 51T brake/suppressor mount in place once I get the upper in hand, but I could also install an AGB at that time if one is really needed.

Have also thought about just going with a Bootleg adjustable carrier and sticking with the Larue gasblock. Doing research now to see if the adjustable carrier gives the same end result as an AGB, realizing there's going to be gas/noise venting from the adjustable carrier vice going down the bore and into the can from an AGB limiting what enters the gas system from the outset.

Any insights or personal experience suppressing a Larue UU upper, or MLGS 18" barreled 6.5G in general, are welcomed

Thanks
 
Sep 16, 2009
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#2
I'm not sure about being 'required" but any precision AR benefits from a few tweeks and an AGB is top of the list. JP silent captured buffer is another.
 
Jul 11, 2010
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#3
Certainly agree with the idea that certain tweaks lead to a better end product, but was more so wondering if the mid-length gas and 18" barrel combo would be putting excessive wear on the upper assembly once the can was in place vice simply not being an optimal set-up.

I'll be handloading for this rifle after burning through 200rds of Hornady American Gunner, so getting a hotter load (with accuracy) will probably be happening. Hence the thought process of putting an AGB in place before the AAC 51T mount or just getting a Bootleg if the upper is slinging brass past 3 o'clock once the can is in place.
 
Jul 11, 2010
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#5
Thanks for the link to the SLR with proper spacing.

I'll be running an AAC SDN-6 30cal can, so I'm thinking back pressure will be reduced a bit based on it being over bore.
 
Mar 16, 2017
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#6
Yes, I'd consider it a requirement for running suppressed. (There are other ways to restrict the gas too, but for discussion we can lump them all under "AGB").

Any AR that's gassed correctly without a suppressor will be overgassed when you add a suppressor. If it's like the majority of ARs and is a little overgassed without the suppressor (this depends a lot on the load too), that just makes the problem worse. If you run it that way suppressed, best case is it just cycles hard and beats the gun up a little more than necessary, worst case is you end up with malfunctions and an unreliable gun.

If it'll be run 100% suppressed, I would absolutely want to tune the gas for that condition. A Bootleg adjustable bolt carrier is great for a rifle that will be used both suppressed and unsuppressed, but if it'll be suppressed full time, restricting gas at the gas block is better in my opinion.

One option that's a little more robust than an adjustable gas block (does the same thing but no adjustments to come loose or get stuck) is a bushing in your existing gas block. There was/is a company selling a kit to do this, but I forget the name. I do it by just tapping the gas block hole for the same size set screw as the retaining screws. The set screw gets inserted up into the gas block, then drilled out in small increments until the gun cycles correctly. Functionally this is the next best thing to having your barrel gas port sized exactly right for your gun. It does take some trial and error and is more work than adjusting a gas block, but is a more robust solution too, because that bushing won't lose adjustment.
 
Jul 11, 2010
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#7
If it'll be run 100% suppressed, I would absolutely want to tune the gas for that condition. A Bootleg adjustable bolt carrier is great for a rifle that will be used both suppressed and unsuppressed, but if it'll be suppressed full time, restricting gas at the gas block is better in my opinion.
This was my thought process as well. Before I put the AAC 51T mount on, may as well take the Larue GB off and slip an AGB on.

Won't have to deal with knocking out or putting in pins, so it should be a relatively painless swap that can save me some headache down the road.
 
Jul 11, 2010
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If it'll be run 100% suppressed, I would absolutely want to tune the gas for that condition. A Bootleg adjustable bolt carrier is great for a rifle that will be used both suppressed and unsuppressed, but if it'll be suppressed full time, restricting gas at the gas block is better in my opinion.
This was my thought process as well. Before I put the AAC 51T mount on, may as well take the Larue GB off and slip an AGB on.

Won't have to deal with knocking out or putting in pins, so it should be a relatively painless swap that can save me some headache down the road.
 

Snuby642

Sergeant of the Hide
Feb 11, 2017
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#12
I run a aac 30 cal can and all I have done was drop in 2 tungsten weights
to slow the bolt slightly, it's easier on the brass as well.

The gas could be turned to off and not hurt the can any, ie a bolt gun.

I'm not knocking the adj setups but do not think you will require all 3 of them.
 
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smokin.338

50/50 to Insanity...
Nov 3, 2013
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#13
You're running a Larue rifled barrel?
I've found the Omega to be high on back pressure.
Negative... BHW
In my experience over various .30 caliber cans... the Omega's blowback is on the lower side. Compare to a Saker or Specwar 7.62 or an AAC 7.62 SDN.


Tuning the gas system correctly is never "overkill".
Notice I said for my build, it's overkill... with an H2 and sometimes JP Silent capture. Suppress is as smooth as when not !
 
Mar 16, 2017
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#14
Guys, tuning the rifle for suppressed use isn't just about making it feel "smooth". Unlock/extraction timing matters, and besides how the rifle feels in recoil, it has an effect on long term durability and reliability as well.

Look at your ejection patterns - if brass is landing at 3:00 or forward with your suppressor attached, the gun is a bit overgassed, regardless how "smooth" it may feel. That depends on the load of course, a hot load of TAC needs more gas restriction than Varget or 8208, but I've never encountered a suppressed AR yet that didn't benefit from some gas restriction for suppressed use. Just using an H2 buffer is generally not enough to get it back to functioning the same as unsuppressed.