Which Adjustable Gas Block for these AR-15 variants...

[SMTGWKD]

I shoot nearly 100% suppressed and have noticed the actions being fairly violent compared to unsuppressed on these rifles. I know a lot has changed in the past 2 years (to my knowledge Syrac and Micromoa are now out of the game) so I'm looking for current input on the likes of SLR, Odin Works, Superlative, etc for the following:

DD 16" 5.56 mid length
DD MK18 10.3" 5.56 carbine length
BCM 9" Pistol Length 300 Blk (I run both subs and supers here with a JP silent captured spring)
18" 6.5 grendel mid length gas system

I'd also be interested which buffers and springs you use with adjustable gas blocks. I assume it really doesn't matter since I'm using the block to adjust, but thought I'd throw it out there...

 

[Yondering]

You can use whatever buffers and springs you want with adjustable gas blocks, but they might as well be standard carbine (or rifle) parts, no reason to use anything else unless it's just what you already have.

The suggestion for gas blocks has no bearing on what type of AR rifles you have now, just pick something that matches your barrel diameters at the gas block journal, and is compatible with your handguards. Most gas block manufacturers offer the different sizes you might need, but .750" is the most common by far. There are so many variations of AR rifles out there now, even with manufacturers changing specs for a given model over the years, that you really need to measure what you have to figure out the right size.

Personally I use Seekins gas blocks; I set them once and leave them, so they do what I need. If you're shooting 100% suppressed, this is all you need; other brands offer detent adjustments which are easier to change on the fly between suppressed and unsuppressed.
I'm strongly of the opinion that the Superlative "bleed-off" blocks are silly though; the whole premise is just marketing fluff for people who don't really understand them IMO, so obviously I wouldn't recommend them.

If you shoot a mix of suppressed and unsuppressed, the best setup I've found is to combine a Seekins adjustable gas block and a Bootleg adjustable bolt carrier. You can tune the gas block for perfect function unsuppressed, and then select one of the four positions on the bolt carrier for suppressed use. That's the quietest suppressed setup I've used yet, and results in absolutely no gas in my face. It's not a cheap combination, but good performance costs $$.

Hope that helps.

 

[BurnOut]

FWIW, I just tuned my 5.56 AR with a Syrac (the project has taken a long time) and the off-the-shelf Gen I JP SCS. Shooting my go-to load for that gun (Fiocchi 50 gr Vmax), i lucked into a single gas block setting that will give me bolt lock back on an empty mag both suppressed (SiCo Omega) and unsuppressed.

Gun is an 18" RRA Varmint running a mid-length gas system.

 

[padom]

SLR clamp adjustable. I have probably 10 of them. SLR customer service is top notch too

 

[SMTGWKD]

Thanks so much for the input!

I just watched a video of the superlative and I think that's off the list. It sounds like a seekins may be a good choice as long as I don't plan on changing it and it's small enough to fit under my rails.

The Odin works has my attention as it has an inconel screw

 

[Sendit6.5]

I went for the superlative block since I can't get Syrac blocks any more. Mainly because I have a dimpling jig that I used for Syrac blocks and the Superlative blocks use the same .500" spacing between the set screws. Plus, they offer a block for the .875" seat that WOA uses on their Predator contour barrels.

I would have gone with the SLR if they used the .500" spacing but I wasn't going to spend another $60 for an additional jig just so I could use SLR. I prefer using a set screw over clamp on. I'm sure the Superlative will work just fine.


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[SMTGWKD]

Now to the details...

The DD slim rail measures 1.08" in diameter
The MK18 rail measures 1.257" in diameter

In your experience, which low profile gas blocks will fit under these rails? The Grendel still doesn't have a rail/handguard so I can choose accordingly.

 

[padom]

Geez, with those ID measurements it will be tough.... SLR AGB meausres 1.40 for set screw and 1.44 for clamp and you will want some clearance. Do your rails have a channel running down the top inside from muzzle to chamber?? If so it will most likely work since the top part of the gas block will go up into that channel. If you have a truly round or square rail then they wont work.

 

[SMTGWKD]

SLR clamp adjustable. I have probably 10 of them. SLR customer service is top notch too

It appears the SLR may be one of the few that will fit under the two rails I list above. Have you had any concern with the screw not being inconel? As I shoot nearly 100% suppressed I likely won't be touching the rifle once set. In your experience, how many rounds before the screw melts down and requires adjustment?

Thanks so much!

 

[padom]

The set screw can be adjusted but will take you working it out, not in per SLR to break if free if you fire a ton of rounds out of it then decide to adjust it again. I have always been told that clamp gas blocks are better than set screw, they make a tighter seal around the barrel. How true that is I dont know and I own both...

 

[Potss]

Best out there by far is the Superlative Arms, quieter with a suppressor and even less gas in the face. SLR is a close second though, I have a few and love them too.

 

[SMTGWKD]

Best out there by far is the Superlative Arms, quieter with a suppressor and even less gas in the face. SLR is a close second though, I have a few and love them too.

Interesting - do you run yours as a bleed off or restrictive? I really don't like the loss of velocity due to bleed off...

 

[steelheadr99]

On my Grendel build I used the Odin Works low profile adjustable gas block and I am very happy with it. It is easy to adjust and has worked well. As for which buffers and springs I use the BCM Milspec Carbine Stock Hardware MOUNTING KIT with the standard carbine buffer with no problems.

 

[Potss]

Bleed off. The <1% velocity loss over restricted (none over normal gas block) is nothing compared to less gas in face and noise to the shooter with a suppressor. Also the hardest to gum up.

 

[Yondering]

Sorry but the bleed off thing is still stupid. The correct amount of restriction with a normal gas block can give you the same results regarding gas in the face and noise; you don't have to vent pressurized gas to get that done.

 

[SMTGWKD]

Sorry but the bleed off thing is still stupid. The correct amount of restriction with a normal gas block can give you the same results regarding gas in the face and noise; you don't have to vent pressurized gas to get that done.

That's the way I've been looking at it - the physics (by my limited understanding) provide the following:

Bleed Off Pros
1. Possibly Quieter Suppressed (subjective at best from what I've seen)
2. Less fouling of the adjustment screw as the fouling is blown out the front
Bleed Off Cons
1. Loss of muzzle velocity as compared to a restrictive block (admittedly similar to regular gas block, but I ALWAYS like increase fps with existing barrel length)
2. Mess under/around handguard
3. Bleed off isn't capable of working with SBR 5.56 from what I've learned - not enough bleed off to substantially reduce gas to the bolt

Restrictive pros and cons are pretty much the inverse of the above. I have a feeling if I purchase a Superlative Arms gas block it will be used as a less expensive alternative to an SLR Sentry that can fit under some low profile rails like the Daniel Defense Slim rail...and will be run as a restrictive block.

 

[Yondering]

The Seekins is a low profile block too; all of my handguards now are slim rails from various manufacturers and I haven't found one it doesn't fit. The only reason I'd get something else is if I wanted click adjustments instead of set-and-forget. There was an Asian adjustable gas block similar to Seekins available for a few years, and I've used a handful of those as well, but they aren't available any longer.

It's also worth considering whether you want side or front adjustment. I prefer side adjustment gas blocks because they're easier to access and adjust. The downside is you may have to machine or grind a small access slot in the handguard, but when done cleanly that can still look good.
Front adjust blocks are OK if the gas block is near the front of the handguard, but are a pain if the handguard extends very far in front of the block; you need a special long hex wrench to access it, and can't easily adjust more than ~3/4 turn at once.

 

[SMTGWKD]

Thanks for the input. I think I have what I need to settle on a solution. I think the MK18 will be a set it and forget it situation as it really hurts to shoot unsuppressed (concussion).

 

[padom]

Id be pissed If I bought an AGB that I had to grind an access hole in my forend to access the adjustment screw... SLR all the way and they give you an adjustment Allen to access from the front of your forend. Their customer service is top notch.

 

[SMTGWKD]

Id be pissed If I bought an AGB that I had to grind an access hole in my forend to access the adjustment screw... SLR all the way and they give you an adjustment Allen to access from the front of your forend. Their customer service is top notch.

I actually just bought 3 of them

 

[Yondering]

Id be pissed If I bought an AGB that I had to grind an access hole in my forend to access the adjustment screw... SLR all the way and they give you an adjustment Allen to access from the front of your forend. Their customer service is top notch.

I wouldn't, because it's easier access and form follows function.

 

[SMTGWKD]

Just a quick wrench in the solution - any experience of adjustable bolt carriers as compared to adjustable gas blocks?

 

[Yondering]

For me - see post #2

I'd consider using just an adjustable carrier if I didn't have the tools to install an adjustable gas block, but don't think they're as good by themselves. It depends a lot on how overgassed the rifle is already though.

 

[SMTGWKD]

For me - see post #2

I'd consider using just an adjustable carrier if I didn't have the tools to install an adjustable gas block, but don't think they're as good by themselves. It depends a lot on how overgassed the rifle is already though.

That's funny - I looked into the seekins but missed the bootleg part! I've researched in a circle back to your post. I won't bias my needs with my limited understanding of the bcg vs agb, but what would you do for each of the following:

All with Omega Silencers
16" DD Mid length - I shoot this out to 1100 yards and the recoil with the suppressor is surprisingly sharp. I want to tame recoil and tame the effect on brass. Currently running an H buffer

10.5" DD MK18 Carbine Length - I simply want to reduce recoil and make follow up shots more manageable while suppressed. Currently running an H2 buffer.

9" BCM 300 BLK Pistol Length - runs perfect with subs but is pretty stout with 110 Vmax. I'd love to reduce recoil but be able to shoot both subs and supers reliably.

All will be shot suppressed, but the 300 BLK seems to require the most use of variable gas switching.

 

[Yondering]

Honestly the decision of what to do with each has a lot more to do with whether you'll only shoot suppressed, or a mix, than what the rifle is and what results you want from it. All of them will benefit from tuning the gas correctly via a simple adjustable gas block, but whether you need two different tunings for suppressed and unsuppressed is up to you.

The 300 Blk could benefit from the switch adjustments on something like an SLR block or a Bootleg carrier, but really should be fully functional with both supers and subs without changing anything. I accomplish this on mine with standard carbine parts and adjusting the gas block to just lock back on subsonics suppressed; beyond that I just shoot it and don't change anything.

 

[SMTGWKD]

Honestly the decision of what to do with each has a lot more to do with whether you'll only shoot suppressed, or a mix, than what the rifle is and what results you want from it. All of them will benefit from tuning the gas correctly via a simple adjustable gas block, but whether you need two different tunings for suppressed and unsuppressed is up to you..

This is good perspective. I purchased 3 SLRs already and was second-guessing my purchase vs an adjustable BCG. It seems that the difference may be as simple as clicking 5 positions on the AGB vs 2 positions on the BCG. Outside of the annoyance of the gas block removal and install it appears to be a solid solution. Thanks again!

 

[A5scott]

Another vote for SLR. Great company, high quality products, including great hand guards.
I'm of the camp that bleed off types are louder because hot-high pressure gasses expanding thru a nozzle rather than thru the can. Plus depending on the orientation of the vent, they can burn thru a suppressor wrap. But otherwise, Superlative are supposed to be very good too.

Scott

 

[Scotts556]

My superlative arms gas is the bees knees. I like it better than the SLR block it replaced. I feel the bleed off gives a better finer adjustment.

 

[Schroedernd]

You can use whatever buffers and springs you want with adjustable gas blocks, but they might as well be standard carbine (or rifle) parts, no reason to use anything else unless it's just what you already have.

The suggestion for gas blocks has no bearing on what type of AR rifles you have now, just pick something that matches your barrel diameters at the gas block journal, and is compatible with your handguards. Most gas block manufacturers offer the different sizes you might need, but .750" is the most common by far. There are so many variations of AR rifles out there now, even with manufacturers changing specs for a given model over the years, that you really need to measure what you have to figure out the right size.

Personally I use Seekins gas blocks; I set them once and leave them, so they do what I need. If you're shooting 100% suppressed, this is all you need; other brands offer detent adjustments which are easier to change on the fly between suppressed and unsuppressed.
I'm strongly of the opinion that the Superlative "bleed-off" blocks are silly though; the whole premise is just marketing fluff for people who don't really understand them IMO, so obviously I wouldn't recommend them.

If you shoot a mix of suppressed and unsuppressed, the best setup I've found is to combine a Seekins adjustable gas block and a Bootleg adjustable bolt carrier. You can tune the gas block for perfect function unsuppressed, and then select one of the four positions on the bolt carrier for suppressed use. That's the quietest suppressed setup I've used yet, and results in absolutely no gas in my face. It's not a cheap combination, but good performance costs $$.

Hope that helps.

Just ordered a Bootleg adjustable bolt carrier I plan to use on an 18" grendel. I will be running it suppressed all the time and wanted your thoughts on the BCG. Not much on the web about it.

 

[Yondering]

The Bootleg carrier - I really like that it's adjustable through the ejection port without taking the gun apart. Most others (Gemtech, etc) seem to adjust from the other side, so you have to remove the carrier from the upper to adjust it. I do wish the Bootleg carrier could be adjusted by hand without tools, but understand the space constraints, and it only needs a flathead screwdriver, knife, tip, etc.

There are 4 adjustment positions with detents. The adjustment is a bleed off style; I'd like to try a restriction style but the Bootleg does work very well.

I got the best results by first adjusting my Seekins gas block for unsuppressed use, with the Bootleg carrier in the "U" (Unsuppressed) setting. Then with the suppressor attached, I figured out which carrier setting worked best for suppressed use; note that you can use different settings for different loads if you need to. Marking the optimal setting with a white paint pen seems to work well for easy reference.

This combination gave me the fine tuning ability of a screw-adjustable gas block, combined with an easy way to switch to a suppressed setting with a clear visual reference. It's not a cheap way to go, so I haven't done it on all my rifles yet, but is worth the $$$ IMO.

 

[Schroedernd]

Thanks for the response. Don't have the funds to do an adjustable gas block and the carrier right now so when I am home next year I'll try just the Bootleg carrier to start.