subsonic ammo isn't

[Mobuck]

The 9mm muffler for the AR9 PDW showed up last week and the mounting adapter arrived today. I'd done some chrony testing earlier and was fairly sure the factory 147 grain ammo was a bit too fast for "movie quiet" suppression. That was proven today so although the muzzle blast is fairly quiet, the downrange sonic signature is significant(even barely above speed of sound larger diameter, flat nosed, and flat based bullets create quite a shock wave). I didn't have much time today but will try some of the other purportedly sub-sonic factory ammo and my known to be sub-sonic handloads in the next few days.
I'm hoping for that totally cool "PFFFT" sound from this setup. As it is, the outfit is hearing safe and had no problem hitting the 3" swinger @ 50 yards.

 

[loaded round]

Your suppressor will never be ''movie quiet'' and you must expect some noise even with subsonic ammo.

 

[TX Nimrod]

To prove what he states, the OP needs to provide chrono data. I’m not saying he’s wrong, but actual data is superior to a guess from a “calibrated ear”.




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[Paul B]

No supressor or "silencer" if you prefer can completely block out the report of a firearm even with subsonic ammo. To do so it would have to be constructed like the muffler of car where the sound passes through a zig zag passage before allowing the exhaust gasses to pass out the tail pipe. No one has yet figured out how to accomplish that feat regarding the passage of a bullet. :lol:
Paul B.

 

[wwb]

No reference to barrel length in the OP....but ammo that is just barely subsonic in a pistol with a 5 inch (give or take a bit) barrel may very well be supersonic if you add a couple inches to the barrel.

 

[Mobuck]

"No reference to barrel length in the OP....but ammo that is just barely subsonic in a pistol with a 5 inch (give or take a bit) barrel may very well be supersonic if you add a couple inches to the barrel."

Correct. I failed to include that part. The AR9 has a 10.5" barrel and pushes the 147 grain "sub-sonic" factory ammo to supersonic velocities. My sub-sonic handloads run 1050 fps from the 10.5" barrel.
A properly sized suppressor with the right ammo should make very little more noise than the sound of the cycling bolt and the loudest sound should be the bullet striking the metal plate downrange.

 

[TX Nimrod]

So, what are these “supersonic“ velocities? Why not state the actual velocity? Enquiring minds want to know....



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[Mobuck]

I'm getting there. Shooting is on a "when time allows" basis these days.
I'd like to be just under 1050 fps but even that will get a sonic crack in some conditions so I have to go lower to leave some tolerance. I tried a few of the Federal 150 grain polymer coated bullet loads and those seemed to stay sub-sonic. Man do they smack the steel with authority.
I may have to drop back to a 7" barrel to get the results I want with factory loads.

 

[TX Nimrod]

I didn’t mean to appear to be combative or to doubt your comment, just curious. The speed of sound at sea level and 68*F is 1125 fps. I can’t see how there would be a sonic boom at lower speeds unless it was very cold or above 15,000 feet.

https://www.weather.gov/epz/wxcalc_speedofsound


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[Mobuck]

The shape of handgun bullets (short, fat, and blunt nosed) causes more air disruption at a given velocity than more streamlined bullets.

 

[98Redline]

Also bullets that are moving just subsonic may have areas around the bullet where the air is still supersonic and will still generate a shockwave.

https://www.youtube.com/watch?v=BPwdlEgLn5Q
Jump to 5:00 for the subsonic info.

 

[Mobuck]

I think I'm about where I want to be on the handloaded ammo. Right at the 1000fps mark from the 10.5" barrel, hearing safe with the muffler, cycles the AR9 consistently, and the bullets achieve .5"+ expansion in water filled plastic jugs. Interestingly, the penetration and expansion are both around 10% less than the full power factory loads using the same bullets display in ballistic gel(ballistic gel performance information taken from numbers quoted on "Ammo to Go" website). My test distance was 20 yards which is more typical of actual use scenarios for a PDW type weapon IMHO.
This level of performance is well within the parameters I feel comfortable applying to the perceived need for the AR9 PDW.