If you had

3 quality suppressors. One for the 9mm, one for the 40S&W, and one the 45ACP

3 identical handguns. Say 3 full size M&Ps chambered for the 9, 40 and 45

Would the 40S&W be the best to suppress with off the shelf ammo?
The 9mm would be supersonic without loading your own or buying subsonic
The 45 ACP has a thin barrel to thread and a short impulse. It would seem to me to be very difficult to suppress

The 40S&W should be the most quiet

I don't see a question. Subsonic centerfire pistol is pretty much all the same dB.

http://www.youtube.com/watch?v=a0cMuEpV ... 3&index=29

Even though both the 40 and 45 are subsonic, the 40 S&W will have much higher pressure than the 45 ACP

In the Form 1s that I’ve built, higher pressure made the baffles work better
These were 22 mono-cores but they worked much better on pistols than rifles
Matter of fact, they worked excellent on pistols and not very well at all on rifles

I’ve also heard the 9mm can be finicky to suppress

JimmyB wrote:I’ve also heard the 9mm can be finicky to suppress

I've never heard that. Subsonic ammo in 9mm is readly available, easy to load if you would rather, but lots of factory out there. Not all 40 is subsonic, only the heavier bullets. Maybe I'm missing something but just how is the 40 running a higher pressure than 45 when both are at <1100 fps.

JimmyB wrote:Even though both the 40 and 45 are subsonic, the 40 S&W will have much higher pressure than the 45 ACP

In the Form 1s that I’ve built, higher pressure made the baffles work better
These were 22 mono-cores but they worked much better on pistols than rifles
Matter of fact, they worked excellent on pistols and not very well at all on rifles

I’ve also heard the 9mm can be finicky to suppress

Every .22 suppressor I've ever used has been quieter on a rifle than on a pistol. The rifles need subsonic ammo to prevent the crack, but the longer barrels really help reduce the signature because of the lower pressure and reduced heat. I'd be very curious to see the design you used that is working better on pistols than rifles, not because I doubt you (no reason to) but because I'm the curious type, and when someone else has an experience very different than mine, I have a desire to understand why.

As for the other question, based on my (non-pro) experience, I would tend to believe the .45 would be easier to suppress due to the lower pressure.

The .40 S&W runs at 35K PSI chamber pressure max, with the .45 running at 21K PSI chamber pressure max. Without my copy of quickloads handy, I can't give you the pressure after 5" for either, but I can assure you the .40 uncorks with a higher pressure in a pistol barrel than does the .45.

JimmyB wrote:Even though both the 40 and 45 are subsonic, the 40 S&W will have much higher pressure than the 45 ACP

In the Form 1s that I’ve built, higher pressure made the baffles work better
These were 22 mono-cores but they worked much better on pistols than rifles
Matter of fact, they worked excellent on pistols and not very well at all on rifles

I’ve also heard the 9mm can be finicky to suppress

I won't say pressure is irrelevant, however in the three pistol cartridges, 9mm is the quietest when subsonic ammunition is used. There is quite a bit of factory subsonic 9mm available, I reload 124 grain bullets for minor power factor and they are subsonic.

Out of a pistol, 147gr 9mm is subsonic without being made intentionally weaker the way that subsonic 22 LR is weaker.

45 tends to be the loudest because there's almost always a big hole in the middle of the suppressor for air to escape from.... bigger than a 45, in fact.

40 is second quietest...
... and 9mm is the most quiet.

22 rifles with subs are quieter than 22 handguns using the same can.

Here is the loudest to quietest:
45
40
9mm
22 handgun
22 rifle

You should note that the 22 handgun is the only one of that bunch that doesn't require subs to be quiet. This isn't because of some amazing technology for 22 suppressors, but because 22 LR needs more barrel than most handguns have to go supersonic -- so even high velocity 22 stays subsonic.

TROOPER wrote:Out of a pistol, ...

Yeah, I'm not sure why the 9mm sub/super distinction is being made based on the idea that you have to buy subsonic ammo since the same issue exists for 40 S&W, 22lr and even 45 ACP. Subsonic and supersonic rounds can be purchased in every one of these calibers and subsonic produces the best suppression results so the 9mm point is moot.

I'm not sure what the thin barrel and short impulse has to do with anything unless the question being asked is about the machining difficulties involved in engineering a suppression device for a particular firearm/caliber combination. Maybe two different issues are being muddled together?

Also, are we talking total number of dB suppressed or final dB value after suppression ... 30dB suppression of a 160dB shot is more efficient as a percentage than 30dB suppression of a 150dB shot but 120dB is a hell of a lot quieter than 130dB ... can someone define what is meant by "easiest" or "best" or "most quiet"?

This topic is vague.

At any rate, the data exists to illustrate and support Trooper's point that the effectiveness of suppression parallels aperture or caliber. Comparing the best designs on comparable platforms it is a fact that suppression ranges from worst to best in calibers from largest to smallest.

When you look at pistol cans, almost all have the same tube only difference is baffles. Thus a 9mm can would have the most volume for the given caliber. The .40 and .45 would more or less off set given the same volume, with the differences in pressure. Thus a subsonic loading (which while there are factory offerings they have been rather scarce in terms of availability) of 9mm would be the least noisy. Its not so much about bore size as it is about volume and baffle design. Since most .45 cans are no bigger than most 9mm as far as diameter is concerned, you have a loss of efficiency.

Now take an osprey in each caliber and you will have similar numbers across the board.