How much noise reduction from a 10.5" 9mm?

Mobuck

My "PDW" AR pistol project is about 1/2 complete and I was able to access a 9mm suppressor for a test run. Function is fine although I'm still using the "endo-mag"/standard AR lower until I get the dedicated Glock lower finished. The issue seems to be the question of just how much suppression I should expect.
Using UltraMax reman 147 HP , I found the noise level noticeably reduced with the borrowed suppressor but not to the extent I was expecting based on experience with 22lr, 300AAC, and even the 5.56 & 6.8 SPC both of which are 2x supersonic. My next step is to check the ammo over my Chrony to see if it's just hot enough to make supersonic and that's the factor.
I did find that even w/o a can, the muzzle blast is NOT the face slap concussion of a 10.5" 5.56 and with the can isn't what I'd term "uncomfortable" although not certifiably "ear safe".
My first experience with a pistol caliber specific can. Am I expecting too much considering this was not a $1000 can (nor is the one I have ordered)?

mark christian

The blast from a 10" 9mm will be nothing like the concussion from a 10" 5.56. 9MM carbines can be surprisingly tricky to suppress. 147gr loads, which are sub sonic in handguns can often reach supersonic velocity in 10 inch barrels (they almost always do in 16" barrel rifles) so you may need purpose loaded subsonic ammo- which is expensive I have 8" and 10-1/2" uppers for my 9mm SBR and normally run only the 8" barrel suppressed.


I use an AAC TiRant 9 can which is modular- you can remove the front third of the can (with the front set of baffles) which reduces its OAL from 8" down to around 5". The longer can with extra baffles obviously gives better suppression, but of course it increases OAL and if I recall correctly, you plan to carry the PDW inside your vehicle where space is often limited.


Just like selecting the correct .22LR ammo, you may have to try several brands of 9mm before you find one which works best for your suppressor/carbine setup.

By the way, if your suppressor has a Linear Inertial Decoupler (LID) device, and most pistol cans do, then you will need to remove the internal spring and replace it with a piston block, which is a metal sleeve that will prevent the piston from moving when it is attached to a fixed barrel firearm. Shooting a LID suppressor on a fixed barrel without the block will pound the piston to death in short order.
L-R: Rear end cap, 1/2X28 piston with the LID spring, 1/2X36 piston shown with the sleeve/block.


To ensure that you cannot screw a 1/2X28 5.56mm caliber suppressor onto a 9mm carbine, 9mm carbines tend to us the 1/2X36 thread.

Mobuck

When I can find a bit more time, I'll run a few of the 147 grain ammo I have on hand (2 choices at this time) over the Chrony just to see if I'm hitting the super sonic threshold. If so, I'll need to find some that will stay sub sonic--may have to go to the slightly heavier bullets.
I will say those heavier, slower bullets certainly slap steel with authority.
In the short term, I'm stuck with nothing more than a "blast forwarder" on the muzzle. That gets me 1/2 way to where I want to be.
Thanks Mark

buschmaster

they probably will be supersonic, and you probably will have to roll your own to get subsonic out of that barrel.

gun shop guy was talking about this exact problem. he sold a bunch of suppressors to a PD and they came back saying they aren't really working, what's up. determined that (you guessed it) the ammo was supersonic out of the 11" barrels. PD says oh no, get us some subsonic ammo. he says that ain't gonna happen with those barrels. they couldn't find any anywhere. PD called Winchester and asked to make them a run of downloaded ammo. no dice. they were out of luck.

Mark is saying "they can be finicky" so maybe he can elaborate on that. otherwise my guess is you got what you got. have to roll your own subsonic.

if you don't make it, and that "blast forwarder" is good enough for you, might think about removing the can and using a cone like what's on a Krinkov. the implosion creates back pressure and helps reliability. that's what it was for, not the muzzle flash.

Mobuck

I can see all sorts of ways a blow back "long barrel pistol" could be problematic when a muzzle device is mounted. The combination of parts required to make the thing work in the first place now hampers function in certain ways. At this point, I have determined that the package will function either open or muffled with the ammo I have. Worst case scenario, I'll give up some level of noise abatement to ensure 100% functionality. The difference between BANG and bang is less important for my expectations than the difference between bang and click.
The "blast forwarder" is only a crutch while enduring the interminable year long holding pattern. If not for the legal hoop hopping, the muffler would be in place by the time the lower is finished.
I still have some options on the ammo choices that need checking out. I see some 147 HP self defense type ammo listed in the high 800's to low 900's fps. This may be from a 3-4" barrel and may still hit 1050 from the 10.5". If so, there's the 158 grain option that might just barely fit the niche. Somewhere in my stockpile, I think I have some 147 Gold Dot ammo that I really want to test. Gold Dots have been a winner for me and I do want to have some expectation of expansion to enhance terminal performance.