Are adjustable gas blocks necessary on short barrel AR’s?

I can see why they might be useful on barrels 16 inches or longer but for anything much shorter say; 5.56 with 11” or less; is it really necessary?

An adjustable gas block may be even more necessary on a short barreled gun. The shorter gas system and ammo loaded for a 14.5" to 20" barrel may or may not function. Adjustability gives you options.

The reason I’m asking;

I have a 10 1/2” with a car length gas port.  I think it’s 7 1/2 inches or perhaps 8”.  I will be using a suppressor most of the time that’s  designed for the 762.

From what I can tell, the gas port is a .075.

Not necessary in the least.

As long as the barrel is ported properly for the length, you can get 100% reliability suppressed and unsuppressed. No requirement for an AGB at all.

A gas port of .075" is a bit on the large side for my taste, especially for shooting mostly suppressed. It'll run, however.

If you want to reduce it down to a more appropriate .070", you can do so with a BRT insert rather than an adjustable if you prefer.

Not really, but I like them a lot when running suppressors to tune the gas system. Standard gas blocks work fine though.

No they are not necessary.

All good info.

It’s good to see all these different perspectives.  It helps a lot in getting a full circumspect.  

Since I haven’t received my stamp for the suppressor as of yet; I guess I’ll wait and see if the results require any adjustments suppressed.

Thank you everyone! This really helps keep  me from getting ahead of myself.

Anyone else feel free to chime in.

My experience across maybe a dozen rifles from 8.5-16" in various calibers is that some need it and some don't. I'd guess out of those it's about 8-9 run fine, and 3-4 needed tweaking.

My advice is to shoot it first, then work on stuff like agb, adjustable carriers, and adjustable gas keys only if needed.

If you want to run a wider range of ammo, they can be helpful. I pretty much only run M193 so for me, no.

It all depends.  I have SBR that work fine suppressed or not.  It’s about gas port size.  Adjustable gives you a chance to fix it.

My 11.5" runs fine both with and without a suppressor using a standard FSB.

All of my rifles suppressed and this is 100% correct. Once you start shooting you you might change buffer, get an adjustable BCG, or gas block. Some cans have a lot of back pressure while others have minimal. Suppressing a rifle creates a whole new system in a way. You have to tailor the configuration to that system

Gas port?

Do you mean the barrel at the gas block is .750?

Don't fuck with the gas port size.

Things will always work better on short barrel suppressed system with an adjustable gas block.

Carbine length is designed to produce more gas than needed to provide maximum reliability.

Adjustable gas gives you options and flexibility.

Agee.  You can use a normal BCG, pinned has block, and if the port size, buffer spring and buffer are a match, absolutely no need for an adjustable gas block.

They're never really necessary, unless your gas port is way to big. I've built many guns from 7" to 20" and never used one.
Adjustable gas blocks can only fix over gassed, not under gassed. You'd be surprised how many people come on here trouble shooting a short stroke issue with an adjustable gas block.

I run a 10.5 car suppressed and I run a spikes T3 buffer and that’s it.  Shoots great and easy to stay on target. Haven’t felt the need for an adjustable gas block.

After trying one, I  put  adjustable blocks  on all of my builds now. I don't see the downside and like the ability to tune the gas how I want it. I also shoot suppressed and unsuppressed, but I would still use them regardless. There's a significant difference in feel when using close to minimal gas.

Yes,  im aware AGB's are for reducing gas flow be-it throu restriction or bleed off for reduction of ware.  Seems most milspec choose a high gas pressure for relyabilaty in a here and now scenario.  It's understandable considering a wide range of environments.   But a private citizen position; if you run a gun hard through training or competition, would it not be beneficial in fine tuning with an AGB?   Seems like the epuipment would last alot longer.  I'm sure the last thing the military would want is a bunch of Corprals or PFC's messing with that and would be disastrous.         No offense to our great military members!!!

My main suppressed 10.3" CQBR with a fixed .070" gas port and MK12 gas block has just under 20k on the bolt, 15k+ on the Damage Industries Enhanced spring and the only maintenance replacement I've done was swapping in a fresh barrel at 17k. I'm not really sure how much longer you could expect parts to last.

Same specs as the military CQBR, which isn't an over gassed port size at all. If anything, Crane selected just about the perfect "do-all" port size for both suppressed and unsuppressed in 10.3.

Please heed krdt in this matter.

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.................................................................................................                       Wow!  Now that is impressive.   I don't have anything close to those numbers.  I guess i'm being a little paranoid about my G2 308...          Thanks,  I'm learner as allways & never stops.

With the price of adjustable gas blocks, I would say it doesn't hurt to have one. Ultimately you may not need it, but at the same time it is cheap enough to not be a huge waste.

A regular low profile gas block will cost about 25-40 bucks, whereas you can get a really nice adjustable one at just about 60 bucks. Not that much more expensive.

That sounds logical.  Never thought subsonic 5.56 was worth the effort.

.300 blackout;  is a cool round but it never really interested me.  
308 makes a terrific subsonic when tuned properly and has a much larger variety of utitlty when going up and down the scale of extreams via super or sub.

Any els who differs, please share your thoughts ??  

Perhaps a new thread could come from this perspective since the original question was of a different origin.

It mainly depends on the barrels gas port and ammo.

Most of my builds only require matching the buffer weight to the build.

I've had a couple of barrels that were way over gassed and needed to reduce it with an AGB.

It's more than probable that you won't NEED an adjustable gas block.  As many have said, it should run fine without it.

Still, after having messed with ARs for a number of years now, it is apparent that manufacturers still have to put out a product that will work with a broad range of ammo.  Many, on this site and others say that if your gas port is of the "correct" diameter, then you don't need an adjustable gas block.  But you have to ask, "correct" diameter for what?  If it is "correct" to allow proper functioning with both cheap steel cased ammo and true M193 spec ammo, it's going to be running more gas than the gun needs to function properly when you shoot hot ammo.

I don't worry too much about wear on my ARs.  If a part wears out or breaks, I replace it.  What I am concerned with is how the weapon shoots.  My latest build is a 10.5" on a Ballistic Advantage barrel.  It ran fine with the gas block that I had, but considering what specialty springs and buffers cost and what they can add up to by the time you've fiddled with this one and that one trying to find the right combination, I didn't think an adjustable gas block was a bad investment.

I'm glad I did it.  I'm now running an ST-T2 buffer with a milspec spring and a standard A2 flash hider and it shoots flat enough that I can keep the dot on target when doing drills.  I'm using an SLR Sentry 7.  Setting 5 for M193 spec ammo and setting 7 or 8 when shooting the cheap stuff.  It runs like a clock and shoots soft.  I don't think I needed it, but I think it was a good investment.  I think I'll be using one on all of my short barrel builds.