Suppressor Anomaly

[Jerry R]

Something interesting happened at the GriffonSec Fall Shoot.

Running an 8.5" 300 Blackout Pistol with, and without, an AAC 762-SD suppressor. Shots fired at 25 yards only, as this was a "sight-in" session. I wanted to make this a dedicated suppressor host for sub-sonic ammunition.

The pistol's accuracy was good without the suppressor, using a variety of sub-sonic rounds. Test included S&B 200 / Winchester 190 Sub-X / and Hornady 208 A-Max. They all grouped well un-suppressed. After the S&B appeared to be something the can didn't like, I eliminated them from the next test.

I fired one group of five, un-suppressed, with the Winchester and the Hornady. I then fired one group of five, suppressed, with the Winchester and the Hornady. The target below shows the results. Again, this was only at 25 yards. I pulled a shot with each of the 190 and 208 un-suppressed ... those are on me, and noted on the target. The RDS is a Romeo-5.

As a side note, I did not see this anomaly when using the 762-SD on the 11.85" PWS MK111 Piston Upper with sub-sonics. So, my thoughts are that this is not the barrel, ammunition, or the suppressor, but something in the combination.

One last item ... this did not happen when firing supersonic ammunition in the 8.5" 300 Blackout, or out of an 8.5" 223 Wylde Pistol, also using supersonic ammunition.

Any thoughts, comments, or opinions are much appreciated. I will be contacting AAC for their opinion as well.

6980

[gatordev]

I may be misreading, but it didn't sound like you shot another group unsuppressed. Is that correct? If you didn't, I'd start there and if it's still wandering, I'd be looking at the optic. If you did and it came back to the first group, then I'm not sure. Maybe the mount is loose?

[Stone]

Agreed, I would pull off the RDS and shoot some groups with the iron sights as a baseline, with and without the suppressor. If you can, do it from a supported and seated position to get the shooters best accuracy...

[Joelski]

Jerry, Are the un-suppressed rounds all in the ten ring and the suppressed ones progressively angling away from the target? Seems as though perhaps the shoulder for the MD is not concentric and perpendicular to the base of the MD, which could consistently angle the can off center from the bore axis. Another possibility is it could be off in a similar fashion and alter the transitional ballistics just enough so that the bullets path of travel is altered. i.e. could the bullet be passing close enough to the baffles to alter it's aero without a full fledged baffle strike occuring? To test that theory, the spread would continue to veer off target at greater distances. Probably not much help, but maybe?

I haven't thrown a scope on my blackout to check for MOA accuracy, or drift at distance. With the red dot, I am keeping it in the pizza box lid at 50 - 80 yards. Any farther and the dot obliterates the target.

[Jerry R]

Sorry I didn't provide enough information. We did shoot unsuppressed after, and the shots were back in the original area, and grouped. We also shot a 16" Sig 716 in 308 after this (with the 762-SD) and the groups were centered and tight. I shot 124g 300 BO supersonics after this, also with the can mounted, and that ammo was centered and grouped. The RDS mount is tight and I used blue lock-tite. We tried to eliminate as many variables as we could.

[Former11B]

What’s the twist rate? I’d inspect the inside of the can very well even for a tiny copper colored spot. Sounds like the gun preferred lighter ammo and while unsuppressed with heavies, the rounds weren’t making contact/ thrown off due to the lack of the can

[Jerry R]

Twist is 1:8. Good idea, I have a lighted bore-scope "snake". I'll take a look. Thanks.

[voodoo_man]

what muzzle device?

[Jerry R]

what muzzle device?

It's an AAC "Blackout 51T Flash Hider".

6984

[Jerry R]

I’d inspect the inside of the can very well even for a tiny copper colored spot.

YouTube video below is from my Endoscope view of the inside of the can. I don't see anything that looks like a baffle strike, but some of the baffles are oddly shaped. The only spots I see on the edges of the baffles appear to be (possibly) flakes burned off the bottom of FMJ's. But ... I don't know what the hell I'm looking at [BD]


https://www.youtube.com/watch?v=4E2UpRuC-c4

[Joelski]

Interesting. I wonder why the hexagoal?

[alamo5000]

Maybe check the mount itself for debris and also the other internal ratcheting parts on the can itself for possible failure points. Either something got stuck on or interferes with the internal mating surfaces of the can (where it mates up with the muzzle mount inside the can) or the mounting system is starting to possibly have issues.

I would get a 1 inch round steel pipe brush and give it a good few twists inside the mount end of the can.

[Jerry R]

Interesting. I wonder why the hexagoal?

Unknown - I am curious as well.


Maybe check the mount itself for debris and also the other internal ratcheting parts on the can itself for possible failure points.

Photo of the mount before cleaning. This was the first time the pistol was fired, mount installed using RockSett, with no shims, and torqued to spec. That is not grease on the threads. The can indexed to the same point each time it was mounted.

6986

[alamo5000]

What about on the suppressor side?

Just to be clear... what is the white stuff? Is that the Rocksett on the muzzle device?

I don't have any AAC cans, but I would put my bet on something on the mating surfaces was causing an uneven blast wobble or it could be a minute uneven space on the barrel itself. For example, when I got my very first can I was excited to try it out so I just put the MD on the gun without timing it. Later on in my evaluation even having the orientation of the bare MD altered would change my POI by a lot. It was very noticeable.

I don't know how locked up that can gets when mounted, but if there was anything caught in between the can's mating surface and the MD's mating surface it can cause things like this. It can happen if the shoulders of the barrel are not exactly even on both sides as well. Both of those things will induce things like this. I helped one guy who had terrible horizontal stringing so I had him remove the MD, clean everything with a stiff brush and install again with shims which he did not have the first time. Problem went away with about 15 minutes of easy work.

[Jerry R]

What about on the suppressor side?

Just to be clear... what is the white stuff? Is that the Rocksett on the muzzle device?

Not sure what you mean "on the suppressor side"

The white stuff is firing residue. The threads only align the can, the teeth lock it up, so there is a little blow-back around the threads. That particular mount does not have to be timed (per AAC) and they recommend not using shims.

The problem I have with this whole situation is, the can works (on this pistol) with super-sonics ... no stringing, and good groups. Only the subs string. One of the other shooters suggested turbulence due to projectile speed; but not enough to cause a baffle strike. Interesting problem, and I'm not sure it can be "fixed". I may have to stick with supers on the 8.5" and use the subs on the 11.85" (which groups well, without stringing - same type mount.)

I'm gonna drop it into the ultra-sonic cleaner, and then brush the insides of the main chamber. But the can probably has less than 300 rounds through it.

And ... I appreciate all the responses, thanks guys.

[gatordev]

The problem I have with this whole situation is, the can works (on this pistol) with super-sonics ... no stringing, and good groups. Only the subs string. One of the other shooters suggested turbulence due to projectile speed; but not enough to cause a baffle strike. Interesting problem, and I'm not sure it can be "fixed". I may have to stick with supers on the 8.5" and use the subs on the 11.85" (which groups well, without stringing - same type mount.)


I missed this before. Seems like that barrel may just not like subs. Why that's the case could be explained by your other shooters, as that's beyond my knowledge, but that might be the issue.

[Jerry R]

Seems like that barrel may just not like subs.

Actually, groups great with subs ... without the can. Target is nothing but groups of the subs with and without the can. This is way above my pay grade too.

[gatordev]

Actually, groups great with subs ... without the can. Target is nothing but groups of the subs with and without the can. This is way above my pay grade too.

I got nothin'.

[Former11B]

The hexagonal baffle apertures are...baffling...me lol

AACs baffles on the inside are manufactured odd and angled due to the process they use, which isn’t finalized with a round wire EDM...the Mini 4 I have in jail looks mostly round but has some small angles I can see once I zoom in and brighten it

I’d email their C.S. and maybe see if theyll pay for you to send the upper + can in

[Jerry R]

Opened a ticket with AAC. Initial question from them was twist rate, and comments on stabilization. I detailed the events, added the target photo and video link in my reply. This was their response:

6987

I explained that we tried three different weights, which were three different brands, and told them to close the ticket.

Oh, well. [BD]

[BoilerUp]

I suspect it is just harmonics. As I've gotten into reloading over the past couple of years I've been surprised to learn how much POI can shift laterally with different loads (i.e., a few inches of lateral shift from changing only the charge by a grain or two)

[Joelski]

Sounds like a magic combination of weight, twist rate and velocity, all interacting in a bad way. As mentioned, harmonics and damping effect by adding the silencer can lead back to the barrel as the main agonist in this combination of poor ballistics. I haven't seen a benefit to having a barrel under 10" (Increased concussive force, increased muzzle flash, increased unburnt powder, etc.), other than the blackout powder allegedly burns off within 8" and I haven't seen velocity-related complaints from the guys shooting 16" .300 B.O.

[Jerry R]

increased unburnt powder, etc. other than the blackout powder allegedly burns off within 8"

Side note: This one is an 8.5" barrel, and the BCG has a crap-ton of un-burnt powder on it.

[Former11B]

Jesus their CS aint what it used to be

Sold out to big business

[cjd3]

Side note: This one is an 8.5" barrel, and the BCG has a crap-ton of un-burnt powder on it.

What powder? My 190 subs are dirty, but all the AA1680 seems to burn. This is on an 8.3” with an Omega.

[Jerry R]

What powder?

Unknown ... all factory ammo so far. Lot of brass saved though [:D]