Home Forums Hunting & Shooting AR and Tactical Rifles I need Help!(suppressor/gas issue...)

Gentlemen, let me start by stating that I am an AR novice. I've had one(or two) for years but never really got into them enough to know anything about how they work, especially in the suppressed form.


That said I recently ordered a CMMG Dissent in 300 BLK and last Friday it showed up at my FFL guy. Friday evening I got it setup to shoot and yesterday afternoon I took it out for a test run.

First shot was with a CGS Hyperian K and Federal subsonic 220's. The second shot wasn't happening as the 'bolt' got 3/4 into battery and stopped. I pulled the charging handle back and the shoulders of the unfired cartridge had little indentations in them and the chamber was filthy dirty with gritty residue.


Cleaned the gun as best I could and repeat the same scenario. Cleaned it again and pulled the can and it shot okay. Action was still gritty but it functioned 90% of the time for about 30 rounds. The 'bolt' would hangup every so often but I think it was just because the action was still dirty.


I am thinking I need to open up the adjustable gas block to help the action work better suppressed but the amount of gritty residue was insane.

Several youtube vids show guys shooting these 'pistols' suppressed without issue so I'm wondering what in the hell is my problem?

Any ideas and advice would be much appreciated, thanks.

Adjustable gas block will surely help keep things cleaner, but they can be touchy with subsonics.

Barry, I've read that it's better to be over gassed versus under gassed for positive action function but by opening up the gas block screw it seems like that would make the rifle run even dirtier or do I have it backwards?


I need a long stem 5/64th allen wrench to adjust the screw and of course I couldn't find one in town so had to order.

Yeah, the more gas you have, the better the action will function... (if no can is used and the factory block works, which yours appears to be working fine without the can)

But the can will add lots of back pressure, so you can adjust to function using less gas with the adjustable block.

There's guys here that know a lot more about that stuff than me. I have a piston rifle with an adjustable gas block that doesn't let anything gas or powder foul back into the action/bolt area. Got friends that shoot gas w/ cans though, and we've had to combine wits to get them functioning cleanly... and I use "cleanly" meaning less dirty.

Okay, that makes sense.

What buffer weight and spring are you using? Are these factory or reloads? If reloads, lots of powders work well for supers, but only a few work well with subs.

I don't have an adjustable gas block, so I use a buffer and spring that gives reliable service with my subs, but is not over gassed for my supers.

When you shoot supers, where is the brass being ejected?

Factory Federal subsonic 220 grain ammo.

This is a funky pistol design, no rear spring.

[quote=SamOlson]Factory Federal subsonic 220 grain ammo.

This is a funky pistol design, no rear spring.



OK, don't know anything about those. I was able to play with buffers and springs to get reliable, clean service with subs and supers. If the gas block is all you have for adjustment, I'd start wide open for the subs and adjust down as needed. The suppressor should add back pressure and make it more reliable and in theory need less gas.
Maybe an issue with those factory loads?

Why not give CMMG a call. My br-in-law bought a 300bo unsuppressed pistol from Gunfighter Tactical and had similar issues with cycling. He didn't know much about ARs at the time and gave it to me to troubleshoot. I ended up calling GunTac. explaining issues. They had me pull off gas block and give them ID on it. He said "sorry we installed wrong gas block". They had installed suppressed gb with smaller gas port. Sent correct and it runs great now.
You mention "gritty residue" and that seems concerning. I've had dirty but never gritty with my ARs.

I just sent CMMG an email describing the issue.

Did some ammo research and found that subsonic ammo uses some type of filler in with the gunpowder? Evidentially that is the 'grit' that blew back through the gas tube.

Ordered some different ammo as well. It'll work out one way or another, thanks for the ideas.

Yikes. Time to load your own. The case is small enough not to need fillers.

no need for fillers is right. Unfortunately with factory ammo you often get what you get. I've tried small charges of even red dot with and without kapok.. Can see no difference. FWIW.

for loading your own subsonics and running a suppressor 1680 is your best friend.
reloader number 7 is very good also. shooters world Blackout is very close to 1680 and works great with some Sonic loads also. VV110 for me it's been the borderline it won't function correctly without the suppressor on but with a suppressor it does.

Powder availability varies, but I can get 1680 pretty easy, so that's my go to for subsonic loads. I use Lil Gun for my supers, which are primarily 125-135gr bullets. I've read issues about 1680 being dirty, but I really haven't noticed. I'm also not running a thousand rounds at a time either.

running suppressed I've not found anything that I would qualify as clean... I run my supers (125gr)with h110/296

Okay, here's a quick update.

I emailed CMMG and got great feedback, they were prompt and helpful.

I sent these pics to the them and they said that the little sand like particles are unburned powder. I had thought the same thing until I read about the filler that is supposedly used in some subsonic ammo.

They also recommended turning the gas screw out a couple clicks. The tech said that when running subsonic ammo even with the can there just isn't enough pressure to begin with to properly cycle the action. This is were I get confused, it would run better without the can than with and you would think there would be more back pressure with the can.

I just emailed them back and asked about that as i was busy working earlier and didn't think about it.

This is after one shot.

Maybe this isn't even dirty but I thought so.

this is awesome I think they'll take care of you this [bleep] is made right here in my own state.. actually know a few people in that factory.. they will take care of you if they do not let me know I will pull what little person things I have

Oh yeah man, I ain't worried.


It'll be a badass little gun when I get it figured out.

Chuck that piece of schit into the Missouri and screw your can onto a 223. Even if a subsonic 300 Blackout is running correctly it's still a rainbow trajectory turd and you might as well have a 22 LR.

Put some fire to that residue and see if, or how, it burns.

Shouldn't be hard to tell if it's powder or filler.

Bro, I'm setting this up for a sub 100 yard barnyard coon pistol.

I have a 223 in the pickup at all times as well!

Yep, and you'll have about a 5" high midrange trajectory with 100 yard zero - enough to miss a raccoon at 50 yards and listen to the bullet ricochet off through the saddle shed.

That's not a bad idea, I might try it when I go to clean the gun.

Truth be known I haven't even looked at the trajectory chart for the subsonic 300BLK.

Might not hurt to do that!

I don't really bother with the subsonic centerfires.

I can get the same quietness out of my .22lr M&P22 shooting suppressed if needed, or a .357 cal integrally suppressed airgun, although I don't mess with airguns much anymore either...

For hogs and stuff I use full power .308's out of an AR 10 that has sound mitigation too. It works for coons on a slow night.

That .308 leaves a nice spray pattern!



Or the .22lr when you don't want to shoot 3 miles... (I love that little M&P22!)

Yeah, the 22 hits as hard as a 240 grain subsonic... solid advice there.. and if you can't deal with trajectory of subs in a 300/221 then you have issues. We kill out to 200 really easy with ours and 198 subs....

Suppressors on direct impingement AR's are insanely dirty. I've heard a piston style is better, but I would think all you're doing is changing where the crud ends up. Seems to me it would foul a piston gun pretty quickly too.

An adjustable gas block on an AR is almost mandatory. You'd also be surprised how much dialing the gas back will cut down on recoil. I have the factory adjustable gas block on my POF Revolution .308, but I've been looking at the ones made by Rifle Speed. No tools required for adjustment and they have index numbers, so you can return it to a particular setting for a specific ammo or sub/super/suppressed use.


RifleSpeed gas block

That's where I'm at too, especially for varmints. Just wasn't seeing that the subsonic heavies were worth the downsides (increased ricochets, increased cost, etc.) over the utility of a rimfire. I had a 17 HMR upper for a while and that was a superb suppressed varmint rig from a terminal performance perspective, but I wasn't quite happy with the upper itself. So a 22 LR it is when going for ultimate quiet and chasing basic raccoon sized varmints.

That all being said these newer expanding subsonic bullets for the Blackout, 7.62x39, and others might make for a better mouse trap. I've used the 190 SUB-X on rabbits thus far at subsonic speeds and they certainly worked.

Lehigh has had expanding bullets for years now. Big holes in deer and pigs. Expanded bullets are over an inch wide....

I’m well aware. The Lehighs are also over a buck a bullet.

led to water....the rest I cannot help with if its a problem.

We’re talking about blasting raccoons here, dollar a piece bullets or 2-3 dollar per round ammo is retarded for such pursuits.

I'm not a sub or 300 BO expert, but those pics of the unburned powder are worse than I've ever seen & are a different matter than just dirt.

Do you get ANY of that unsurpassed.

We built a BO for my son & basically had no issues even close to yours.

MM

Not all gas blocks are the same.
Superlative arms makes some GBs that vent out the front.

Good product from my experience.

Piston driven helps, especially with a can, a lot less gas in the upper, and cleaner.

Personally I lile a piston system, but thats not how they were designed. There are some negatives, but I think the positives outweigh the negatives.

I have a 8" 300 BO in a piston driven, functions reliably. I had some issues getting it dialed in, I found it nearly impossible to setup and function with both 150G and subsonic 200G plus.

Finally decided to be happy with 200G subs as that was more or less what I wanted to shoot.

You might try some different ammo as your pics of the upper look pretty dirty.

There's a saying that ARs schit where they eat, especially true with a can. LoL

All I know is I have a flow through can and it’s not even close to what your pic showed. I don’t think that’s normal for DI and even old school cans. Something is not right for sure.

Just cleaned my 300BLK after 200 rounds suppressed. Was dirty, but not a single grain of unburned powder.
I'd try different ammo. Something just doesn't seem right. Even if it doesn't cycle correctly, it should still burn all the powder.

The CGS suppressor is a high back pressure design, trapping lots of pressure that goes into the action when it opens, so it's going to be problematic on an AR.

It's very possible the high back pressure can combined with ammo that is not burning the powder is the issue. I have never seen that kind of fouling.

High back pressure cans are great at reducing the signature at the muzzle but have a down side in the AR as the action opens before the can "blows down".

Like most things there are tradeoffs. The best bolt gun suppressors are not the best AR suppressors.

Gentlemen, I have an update for you regarding the Dissent.

I got a hold of the right allen wrench, it's a 3/32" not the 5/64" that is listed on CMMG's gas block info page. I also ordered some different ammo and that showed up earlier this week.

So I get the allen wrench and screw the adjustment screw all the way in and record the number of clicks, 18-19. I then back it out 10 clicks and fire a round. Bolt doesn't move at all. I then back out 10 more. Gun goes bang and cycles the next round and ejects the empty about 3 o'clock. I inspect the receiver area for dirtiness and there is none. I then shoot a couple more and zero issues, spent brass is still landing at 3 o'clock so I turn the screw out another click. We are now out around 2-3 clicks from factory setting.

Should note that I am shooting Winchester Super Suppressed 200 grain. I then load up 10 rounds and zero issues and no sign at all of powder flakes. Load up another 20, no issues, repeat, no issues and no sign of powder residue. Sweet!

I then load up some of the Federal 220 grain that I shot the original time and here is the weird part, they cycled fine and showed no sign of dirtiness. I can't figure that out but I'll take it!


So what in the hell caused the gun to be so dirty initially but now it runs fine for 50-60 rounds and no sign of powder flakes?

Bullets can get pulled out of the case in semi autos with the power spilling into the action.

That amount of power would be consistant with a bullet pull and power dump.

One wants to be sure the bullet is not still in the barrel if there is powder in the action.

and this is the Burns we can all appreciate.

not the Rick and Johnny jack off show that's currently going on in a few threads tonight.

Who knows, but at least you've got it working now.

I set mine up to eject the subs around 4:30. That puts my supers at 3:00. Maybe not ideal for the supers, but it runs both without any issues so I can switch back and forth without any adjustments.

Great news, Sam!

Okay guys, thanks for the input.

I made a crude vid yesterday to try and see how the pistol operates without the use of a brace. And as noted in the comments someone pointed out the inconsistent brass ejection.

And I obviously had a brain fart and was off 90 degrees in my incorrect description of ejection at 12 o'clock.

Do you think the ejection variation is ammo, gun or related possibly to inconsistent pistol grip?


And obviously I don't intend to actually shoot the pistol like this in any serious situation, this was simply a test.

Trying to remember but I think the gun had more consistent ejection with the brace but I'm not sure.


And please don't make fun of my winter beer belly...lol

The ejection pattern looks pretty good. They say 3-4 o'clock or so is about right.

Most of the variation is probably the variation in how it's being held from shot to shot.

Thanks Shane. It was beyond awkward shooting the pistol with the scope like that but I had to try just to see what the hell would happen.

Just ordered some more subsonic ammo(Sig 220's and the Winchester 200's I was shooting in the vid) to test out in this thing and will have to remember to set the camera up when testing the ejection.

I'm still wondering about the first couple shots that I fired both of which were suppressed out of a brand new suppressor.

Is it possible for chit inside the suppressor to get blasted back into the gun?

Google.

https://www.reddit.com/r/NFA/comments/17bv3mx/cgs_hyperion_excessive_particulatedebris_from/

There's a sling technique you can use to get a lot more stability even without a brace. Basically, pushing the pistol forward against sling tension to tighten everything up.

I've played with it a bit with a AR pistol. With the AR style the buffer tube on the cheek makes another point of contact to help stabilize the whole works.

This is a single-point sling technique,

A technique with no sling or brace,

Two-point sling technique,

Thanks again Shane, more research for later when I get home and out of this wind!