Suppressed AR15 - Observations & tuning.

[IndianaBoy]

Last year I picked up an AAC 556SD.

AAC was running the Damn The Man promotion and a local shop was doing $100 off for Black Friday. Too good of a deal to pass up.

Initial host was a 16" carbine gassed AR with a semi-auto carrier and an H2 buffer.

http://img.photobucket.com/albums/v239/gnieman/1432914553033_2096830537_7c713306_resized_zpsm6jplfb2.jpg
Even with the RTV sealant I would get a fair amount of gas to the face. Charging handle is a BCM gunfighter.


I wasn't satisfied with my only suppressor host being an iron sights only rifle so I parted it out and put together a new upper.

16" mid-length. M16 carrier.

Now I was waiting on a UBR to finish out my lower build the way I wanted it so I put the new upper on my 3-gun lower initially which has a JP captive spring setup to mimic the JP Low Mass buffer.

http://img.photobucket.com/albums/v239/gnieman/20151122_091202_resized_zpsv9pyria2.jpg
The volume of gas was much much less but I could still feel it on my cheek.


Then the UBR arrived and I had everything setup like I wanted it. Upper does not have a forward assist installed. I considered getting the gas-bleeding replacement that goes in the forward assist port because I thought that gas venting out of there might come right back into my face. That is not the case so my plan now is to leave the forward assist assembly out entirely.


With the setup as it is now.

http://img.photobucket.com/albums/v239/gnieman/20151222_010618_resized_zpslsdnbamn.jpg
Mid-length gas. (not sure on gas port size.)
Standard low profile gas block (I figured I could always add an adjustable later if it was really warranted.)
M16 carrier, H2 buffer, bcm charging handle with RTV sealant.

I am getting no discernable gas to the face/cheek whatsoever.

Another thing that is harder to quantify is that it seems like the ejection port pop is markedly reduced. I always felt like my old carbine upper was way overgassed and the addition of the suppressor exacerbated that situation. New upper seems much much quieter as far as I can perceive it. I presume that delaying unlocking with both the added weight of the carrier and more properly regulated gas would give the gas more time to expand and cool, and let more of it vent out the end of the suppressor rather than back down the barrel.


Mid-length upper runs great suppressed and unsuppressed. Zero shift is minimal but honestly I don't plan to shoot it with the can off. Recoil is very mild and that is comparing it to my tuned 3-gun setup that simply doesn't move.


So in my experience an optimized gas port location, adding some mass to the equation and a few small tweaks to the upper setup have made a tremendous improvement in the performance of my suppressed rifle.


Ancillary benefit. The new upper is much more accurate than the old one.

Overall I am very impressed with the performance of the suppressor.

[jmnielsen]

Since it seems like you built your uppers, why didn't you just get an adjustable gas block like a Syrac or similar?

[IndianaBoy]

Since it seems like you built your uppers, why didn't you just get an adjustable gas block like a Syrac or similar?

I've used them in the past. Still have one on my dedicated 3-gun upper. (JP.)

Never totally satisfied. You either loctite the shit out of them and then shoot them enough to trust the loctite +carbon to have them stuck where they need to be, or you leave them un-loctited and worry about them self-adjusting on you. Even the Syrac is known to freeze up if you leave it set for too long.


I considered the Micro-MOA which looks to be a real viable solution to have a block with a unsuppressed-suppressed-adverse setting that always works.


It was a given that I was going to an optics setup and I sold my old barrel for nearly the $ as my new barrel so slapping an adj gas block on the old barrel was not an attractive option.

Went melonited over chrome lined with the new barrel. Old barrel never blew my skirt up in the accuracy dept. so I was happy to divest it.


I am still considering an adjustable gas key although at this point I don't see the necessity.

The performance is much improved with what I have done so far and I don't think there is much left to glean and I don't plan to run the ragged edge of reliability with this rifle at all.

[redmist]

If you can choke the gas at the key, or in the carrier the excess will vent out of the clover leaf vent in my experience. As an example, look at this hand guard. That's 2000 rounds rapid fire, and 1000 rounds FA with the gas choked at the key on the first 2000 rounds.

Ryan

https://scontent-sea1-1.xx.fbcdn.net/hphotos-xpa1/v/t1.0-9/12107069_995687590452070_1292480009611470074_n.jpg?oh=be76b97efa02f520df58bfc116c23e68&oe=57223E97

[mic2377]

I also have a suppressor, albeit a Form 1 unit one intended for use on my 300 BLK, 5.56, and 308.

I originally ran it on the 300 BLK. It works great and besides subs being dirty due to low-pressure, works great.

I have also used it on my 18" rifle-gas 5.56. It is intended for 3 gun and has a smallish gas port. I get ZERO gas blowback, probably because it is 30 cal can on 223 and it is very conservatively gassed.

It makes sense that the different uppers would sound different. I have also used my can on my 308 AR, and it is much louder and more "gassy" than either of the smaller weapons. It is also much more heavily gassed.

I also agree that adjustable gas blocks are really a stopgap measure. I still use one on my 308 AR but a properly gassed weapon should be able to function suppressed or unsuppressed without one.

[Benito]

I also have a suppressor, albeit a Form 1 unit one intended for use on my 300 BLK, 5.56, and 308.

I originally ran it on the 300 BLK. It works great and besides subs being dirty due to low-pressure, works great.

I have also used it on my 18" rifle-gas 5.56. It is intended for 3 gun and has a smallish gas port. I get ZERO gas blowback, probably because it is 30 cal can on 223 and it is very conservatively gassed.

It makes sense that the different uppers would sound different. I have also used my can on my 308 AR, and it is much louder and more "gassy" than either of the smaller weapons. It is also much more heavily gassed.

I also agree that adjustable gas blocks are really a stopgap measure. I still use one on my 308 AR but a properly gassed weapon should be able to function suppressed or unsuppressed without one.

I'm not a firearms expert, but isn't any gun that's properly gassed unsuppressed going to be over-gassed when suppressed?

[IndianaBoy]

I'm not a firearms expert, but isn't any gun that's properly gassed unsuppressed going to be over-gassed when suppressed?

To a point, yes I would agree with that. However there is a happy medium where a rifle is completely reliable unsuppressed while not being absurdly overgassed with a can. Especially with high quality, consistent ammo.


While I use one on my 3-gun rifle, IMHO, adjustable gas blocks are the addition of a failure point. I think tuning with mass and springs can accomplish a portion of the same goals.

[mic2377]

+1 to what IndianaBoy said. There is some latitude to where the gas setting that will allow safe, reliable function. Some configurations are more amenable to this than others, and some companies do a better job getting the gas port "right."

An example of this is my 16" 300 BLK, which has a Noveske pistol gas barrel. Despite having a fixed/pinned block, it runs with 100% reliability in all configurations - subs/supers both suppressed and unsuppressed. There is no doubt that it is probably somewhat overgassed with supers/suppressed, but recoil is not excessive nor is the brass beat up. This is about the most extreme example possible but illustrates that adjustable gas is NOT absolutely necessary.

There is no question that the adjustable blocks are less reliable.

[TheChunkNorris]

Know my experience is a little different because I'm shooting a MR556 10.4" SBR but relates to the buffer/spring combo. It's no secret that the HK has an over-gassed system which helps in adverse operation and HK MR556s come with vented gas blocks. 14.5/16.5" HK416s run in that same gas block configuration with the swivel loops being the only different between MR556s, MRs don't come with those attachment points. Blow back isn't bad at all and that has more to do with the fact that the HK is a piston.

An HK416 in 10.4" runs a non vented(plugged) block. I bought a real deal chrome lined 416 light profile barrel and it came with the correct block. After putting that upper on the MR lower, I'd often run into some issues when shooting suppressed. Being that adjustable gas blocks aren't available, the other options is the buffer system. After going with a Vltor A5, 10z buffer and Wolff rifle spring... no more feeding issues and it runs 100% now.

[Brahmzy]

You need to look at the SLR titanium adj gas blocks.
They're on a whole new level of reliability for FA/Suppressed fire.
Even Syrac can't touch the reliability of SLRs latest Ti blocks.

[ArmsUnlimited]

I have ran thousands of rounds through a Colt 10.3 in standard configuration using a SureFire SOCOM suppressor and have never had any cycling or other issues. No need to adjust gas, those suppressors were designed for use with standard Colt rifles.

Piston guns seem to have issues with suppressors, point of aim point of impact being way off. There was a police department I dealt with who had PWS piston rifles and bought surefire suppressors. Well the shots were way off when they fired suppressed and they were convinced it was the suppressors, until they saw the suppressors ran on a military spec Colt rifle.

I've had many bad experiences with AAC suppressors and steer people away from them when I can. Especially the handgun suppressors

[BufordTJustice]

You need to look at the SLR titanium adj gas blocks.
They're on a whole new level of reliability for FA/Suppressed fire.
Even Syrac can't touch the reliability of SLRs latest Ti blocks.
I've got one on my soon to be suppressed 11.5" Sionics with reduced size gas port. It will be my second SLR Ti adjustable block, the other is several thousand rounds in on my 18" faxon gunner profile with .081" gas port.

As Brahmzy stated, it's wholly different and better than Syrac. I use barrel dimples, Knurled cup tip set screws, Resbond 907TS/Loctite red 271, and green Loctite 620 sleeve retainer on the gas block journal.

Zero gas leakage. None. The fouling around the adjustment screw seals that up in under a hundred rounds. You can still adjust, but leakage virtually disappears after that.

And you'd need a damn hydraulic press to get it off.

[Benito]

To a point, yes I would agree with that. However there is a happy medium where a rifle is completely reliable unsuppressed while not being absurdly overgassed with a can. Especially with high quality, consistent ammo.


While I use one on my 3-gun rifle, IMHO, adjustable gas blocks are the addition of a failure point. I think tuning with mass and springs can accomplish a portion of the same goals.

Gotcha. OK that makes sense.
For buffers and springs, would one of those heavy buffers and something like a Red Sprinco spring be enough to tame an overgassed beast?


+1 to what IndianaBoy said. There is some latitude to where the gas setting that will allow safe, reliable function. Some configurations are more amenable to this than others, and some companies do a better job getting the gas port "right."

An example of this is my 16" 300 BLK, which has a Noveske pistol gas barrel. Despite having a fixed/pinned block, it runs with 100% reliability in all configurations - subs/supers both suppressed and unsuppressed. There is no doubt that it is probably somewhat overgassed with supers/suppressed, but recoil is not excessive nor is the brass beat up. This is about the most extreme example possible but illustrates that adjustable gas is NOT absolutely necessary.

There is no question that the adjustable blocks are less reliable.

I have read this before about adjustable gas blocks.
Having installed an SLR Sentry on my AR-10, I am curious what specific failures people have experienced - e.g. stuck adjustment screws, etc.

[tom12.7]

I'm not really in this game anymore, so I have no real dog in the fight.
I have a strong preference to dedicated porting. Porting that gives other options is preferable to those that do not easily. I would much rather do a simple buffer swap to attain an intended goal than to go into other unknowns.
A system is balanced out better in general for function overall, if that system has the option to increase or decrease action mass for prefered function.

[TheChunkNorris]

I have ran thousands of rounds through a Colt 10.3 in standard configuration using a SureFire SOCOM suppressor and have never had any cycling or other issues. No need to adjust gas, those suppressors were designed for use with standard Colt rifles.

Piston guns seem to have issues with suppressors, point of aim point of impact being way off. There was a police department I dealt with who had PWS piston rifles and bought surefire suppressors. Well the shots were way off when they fired suppressed and they were convinced it was the suppressors, until they saw the suppressors ran on a military spec Colt rifle.

I've had many bad experiences with AAC suppressors and steer people away from them when I can. Especially the handgun suppressors

Is that observation with the AAC can or the PWS? At 100 yards with a 10.4" barrel and a Saker 556, I'm about 1.5" from point of aim. That is from my HK MR556. My LWRC M6-SL is about the same and has a 16" barrel.


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[MistWolf]

Getting an AR to run properly is a balancing act. Yes, you can tame an over gassed beast with a heavier buffer and a stiffer spring, but excess gas is still vented at the receiver. A suppressor only makes the situation worse.

It turns out Colt originally designed the gas system of the M4 to run with an H buffer, carbine spring and (if I recall correctly) a .0625" diameter gas port. Later, they switched to an H2 buffer for M4s with burst/full auto fire.

Tuning an M4 to run on a heavier buffer, like an H3, means more gas to the face.

I have an SLR adjustable gas block on a shorty AR and have put a few hundred rounds through it with no problems. I almost went with the Syrac, but fortunately, CoryCop firmly guided me to the SLR, for which I'm grateful. The SLR does have a couple more moving parts, but its usefulness far outweighs the added complexity

[henschman]

I'm glad you found a setup that works for you. I would be interested to hear the details on which components you went with, particularly the barrel. Always nice to see mfg's properly sizing their gas ports.

I hear what you're saying about the old straight set screw gas blocks... I had a JP on a .308 build, and it is nothing I would trust for a fighting rifle or anything like that... but I went with a SLR sentry on my recent SBR build, and it is a great design. It has detents with click adjustments, which solve the problems of the screw self-loosening, and allows for repeatable adjustments for switching between suppressed/unsuppressed.

[tom12.7]

While I appreciate the understanding in function that some may have observed with adjustable gas blocks, I am less than convinced that there is a commercial product that could be issued for possible serious use.