Adjustable Gas blocks for AR-15

[loose noose]

I'm sure this subject has been covered before, and hopefully I'm on the proper forum, to ask. Unfortunately, I couldn't find anything on my search.

My question is are these new adjustable gas blocks all the they are cracked up to be, in fact does that little screw go in or out in order to create enough pressure to eject the empty casing. I'm a bit confused, as I've built quite a few new rifles (AR-15's) for myself and friends but never before have I built one with the adjustable gas block. Perhaps I'm ignorant but I just can't seem to figure it out. I believe it is an "SG" or "SJ". Sorry I can't be more specific.

 

[LoonWulf]

you likely have a restriction type gas block. There should be TWO little screws, the larger one actually adjust your gas flow, and the smaller locks the larger in place (if you already knew this sorry, ive seen guys mistake the smaller one for the adjuster). Basiclly the screw acts as a plug to block flow from your barrel to your gas tube. So to increase gas flow, you back the adjustment screw OUT, to reduce flow you turn it IN.
One thing to keep in mind, with restrictive type blocks is gas flow will eventually erode either the screw or the block itself, cheaper the block, hotter you get it (and the higher pressure your ammo is at port) faster this happens. This means youll need to adjust your block from time to time, and perhaps replace parts as they ware.

The other type of gas block is the Vent/bleed off type, which diverts a portion of the gas to atmosphere at the gas block. These are supposed to be cleaner and cooler than restrictive types, but ive not used one so cant offer any first hand experience.

 

[Telekinesis]

The other type of gas block is the Vent/bleed off type, which diverts a portion of the gas to atmosphere at the gas block. These are supposed to be cleaner and cooler than restrictive types, but ive not used one so cant offer any first hand experience.

I have one of those vent type adjustable gas blocks from Superlative Arms. Well, I've had about 4. None of them worked and they got sent back to the manufacturer for various reasons such as bolts/gas keys shearing off (even when not torqued beyond spec) and such. Now after 4 months of warranty exchanges, the 4th one doesn't provide enough gas to lock the bolt back at max pressure setting. Looks like I wasted about a hundred bucks and will still have to go back to another gas block (probably a standard fixed block).

I really like the idea of the design, I think it's got promise, but execution of the Superlative Arms block leaves a lot to be desired. I would not recommend them at all.

 

[bangswitch]

I think you can do without an adjustable block if you have the rifle set up correctly and use it the same way all the time. Adjustable blocks can come in handy if you suppress, to keep from over-gassing the action when not suppressed. That said, I put adjustables on both my AR uppers; my 300BLK is probably the one that can use it, since there are so many types of loads possible, and it is a popular caliber to suppress. My 6.5G has one, it came with the barrel/BCG combo. I have it adjusted full open, at 3/4 it would occasionally short stroke.

 

[RainDodger]

I have never worried about it, through seven separate builds. I figure it's one less thing to mess with, one less thing to worry about adjusting (although it isn't difficult), and just one less potential problem with a rifle. Every rifle I've built works just fine with a non-adjustable gas block, providing you have the right buffers installed for the length gas tube you're using, etc. That's just my opinion of course.

 

[MistWolf]

Tube length has nothing to do with what buffers need to be used. What's important is gas port size. Adjustable gas blocks only work if the gas port diameter is too large for the configuration. An adjustable gas block cannot make up for too little gas flow.

Heavier buffers and spring rates can make up for too much gas flow only to a certain degree. It's better to set up an AR with the right buffer (H, H2) and spring and set gas flow to match. An adjustable gas block is an easy way to do this, especially when adding a suppressor

A venting type gas block is not cleaner. The FAL uses a venting gas block and there is plenty of fouling at the vent.

 

[Jackal]

I've used OdinWorks, Superlative Arms and SLR adjustable gas blocks. They all work great. For non silenced rifles, they are unnecessary. Once you add a silencer, they become a requirement.

 

[cougar1717]

Adjustable gas blocks are also useful for AR pattern rifles in calibers with significantly more powder capacity than 5.56, especially when you'd prefer a carbine stock. For reloaders of AR's in 50 Beo, 450 Bushmaster, 458 socom, or a LR308/AR10, and others that have powder capacities in the 30's to 40's (in grains) - they maximize the case life by reducing the amount of gas used to cycle the action. This slows the action down and allows the chamber pressure to further reduce before the case is extracted. These applications usually need more than the maximum available carbine buffer weight.
Adjustable gas blocks are nice, but not really necessary for 5.56, unless you have a race gun with ammo tuned for one load or you like tax stamps.

 

[MistWolf]

For non silenced rifles, they are unnecessary

Not necessarily so. Many AR barrels are grossly over gassed and an adjustable gas block is the simplest way for the owner to properly set gas flow

 

[ewlyon]

I have the JP adjustable block on three different AR barrels. They allow very easy tuning of the gas system. For me they are worth it just so the brass all lands in a small pile nearby without being dinged on the way. It also seems like the rifles shoot a bit smoother but that is just subjective.

 

[ford8nr]

I put one on my SW this past fall and tuned it for my hand loads. My loads are actually light around 2700 fps, so factory loads will definatly cycle the gun. I was surprised how far down I could turn it before I failed to cycle. My goal was to reduce recoil pulse for shooting timed tactical matches. Shot a match this past weekend and it was MUCH easier to stay on target for multiple shots.

 

[glc24]

Well maybe they aren't necessary, but I like the ability to "fine tune" my gas system. Plus having it suppressor ready is nice too.

 

[LoonWulf]

I personally liked adjustable blocks so i could in the past run a few different caliber and length uppers from the same lower with the same buffer/spring combo. While running all of them full open worked the action fine, a couple were way over gassed installing adj blocks on them allowed me to turn them down for smoother cycling while maintaining my less heavily gassed uppers reliability.

 

[Arizona_Mike]

I have a bunch of the no-longer-made Syracs (restrictive) and they work well. The Superlatives are supposed to work in either restrictive or bleed-off mode depending on user choice. In theory restrictive work better with silencers (high bleed off is why AKs don't suppress well). Some bleed off fans say in practice they are actually quieter in real life applications. It has the potential to become the next Ford vs. Chevy debate of the gun world.

In my experience, an adjustable gas block is the best way to tune an AR short of adding more and more ounces of buffer. In fact I run empty C buffers in my adjustable gas guns. It is also the best way to get short barrels, non-standard calibres, silencers, etc. to run right without drilling your own gas ports in the barrel.

Mike

 

[Decoy80]

Just my $.02 on the restrictive blocks. If you can get hands on some Nuclear grade anti seize a little dab sure keeps it easily adjustable. I hated it when I was working and had to use it daily as it wears off the skin and gets off your clothes only when you throw them away. I could have got all I wanted for free and a few years ago I found some on eBay someone else probably brought home from work and got two cans for 40 bucks. I use it on any bolt that im afraid may have to be removed in the future that could possibly seize up. If automakers used it only on exhaust bolts it would save untold amounts of labor replacing parts.

 

[ford8nr]

Problems with ADJUSTABLE gas blocks. Sighted my AR in Friday for a match today. When I got home Friday I noticed a backed out screw on the gas block. Having a senior moment and thinking it was the set screw I turned it I tight - WRONG. Shot the match today, first shot no eject ? Second shot no eject. Shot 20 rounds like a straight pull bolt action. I turned the gas port screw all the way in. Pulled the hand guard and set the screw back to original setting and tightened SET SCREW. Will have to function test it before next weekends 3 gun match.

 

[MistWolf]

The SLR adjustable gas block uses a set screw with a detent. It doesn't back out. The occasional drop of lube keeps it from seizing up

 

[Varminterror]

I've never had any issue with screws backing out in JP gas blocks. Have been very happy with them.

 

[Jackal]

With all the choices available on the market, there is no reason to buy a set screw adjusting gas block over the superior detent styles widely available now.

 

[Varminterror]

There aren't many clamp on style detent types, and none as cheap as the set screw style. Not sure I've seen clamp on detent's besides the JP and the SLR, both of which cost about twice as much as the set screw BTE, and 30-50% more than the set screw JP.

If a guy is bouncing between loads, or switching from canned to open muzzle fire, detent types are almost a necessity. If a guy is just wanting to meter his gas for a given load, it's not an advantage to use a detent type.

Besides, the same opportunity for fouling to seize a detent type exists, just as it does for a set screw type. Most of them are still a simple set screw which is scalloped at multiple increments per turn. The only difference is just a ball detent holding the gas limiting screw from turning instead of a thread-bearing set screw.

 

[Oldhandloader]

I've used OdinWorks, Superlative Arms and SLR adjustable gas blocks. They all work great. For non silenced rifles, they are unnecessary. Once you add a silencer, they become a requirement.

Jackal
Do you have a recommendation for an adjustable gas block for the Remington R-25 (308 cal) rifle? I am using a suppressor and it short strokes particularly on the first 2 or 3 shots. I found one but did not have the pic rail on top for open front sight. There is also a lot of blow-back through the back of the receiver; ordered a special charging handle with deflector.
Any advice would be greatly appreciated.

Dan
Louisiana

 

[Jackal]

You are going to have a lot of blowback regardless. An adjustable gas block will help a little, but the vast majority of blowback actually comes through the chamber, not the gas tube when shooting with a silencer attached. Thats the reason so many people are disappointed with piston AR rifles when they discover that they do little to nothing to combat silenced blowback. As for the R25, I assume it uses a .750 gas block. Its probably not short stroking, its likely just giving the appearance of a short stroke due to over gassing. Currently there are very slim picking for railed adjustable gas blocks of any quality, most good detent adjustable gas blocks nowadays are low profile, made for sitting under free float rails. I strongly recommend either SLR or Odinworks. Both make a good adjustable gas block, with detents, that dont seize up instantly. I used the SLR because the Odinworks wouldnt quite fit under my ultra thin handguard. The SLR on my DPMS GII works great. I have the extra Odinworks adjustable gas block I could offer you for a pretty deep discount if you need it.

 

[Oldhandloader]

You are going to have a lot of blowback regardless. An adjustable gas block will help a little, but the vast majority of blowback actually comes through the chamber, not the gas tube when shooting with a silencer attached. Thats the reason so many people are disappointed with piston AR rifles when they discover that they do little to nothing to combat silenced blowback. As for the R25, I assume it uses a .750 gas block. Its probably not short stroking, its likely just giving the appearance of a short stroke due to over gassing. Currently there are very slim picking for railed adjustable gas blocks of any quality, most good detent adjustable gas blocks nowadays are low profile, made for sitting under free float rails. I strongly recommend either SLR or Odinworks. Both make a good adjustable gas block, with detents, that dont seize up instantly. I used the SLR because the Odinworks wouldnt quite fit under my ultra thin handguard. The SLR on my DPMS GII works great. I have the extra Odinworks adjustable gas block I could offer you for a pretty deep discount if you need it.

Jackal,
Sound advice. I appreciate the offer but I think I will do the SLR as you did. My set up is similar to yours and I ain't going to argue with success. I think I will start wearing chemical goggles the next time I shoot with the can---that blow-back is a bitch.
Thanks from the deep South and keep your powder dry.
Dan

 

[loose noose]

I'm just a simple type of guy, reckon I'll just go with the standard gas block designed for the .223/556 cartridge and be done with it.

 

[IndianaBoy]

I have one of those vent type adjustable gas blocks from Superlative Arms. Well, I've had about 4. None of them worked and they got sent back to the manufacturer for various reasons such as bolts/gas keys shearing off (even when not torqued beyond spec) and such. Now after 4 months of warranty exchanges, the 4th one doesn't provide enough gas to lock the bolt back at max pressure setting. Looks like I wasted about a hundred bucks and will still have to go back to another gas block (probably a standard fixed block).

I really like the idea of the design, I think it's got promise, but execution of the Superlative Arms block leaves a lot to be desired. I would not recommend them at all.

I don't see how an adjustable gas block would cause gas keys to shear off?


Since they can only reduce gas, not increase it. The only way that I can see this happening is with improper installation causing the carrier key to impact an improperly centered gas tube. It is an easy enough thing to do. It doesn't take much misalignment to cause some contact there.

I would venture a guess that your fourth example may not be centered over the gas port on the barrel.