OK, I have a firearms realism question about 9mm vs. .45 ACP which, shockingly and potentially disappointingly, does not have to do with "stopping power". Instead, it has to do with suppression.

My understanding is that if you wanted a truly silent firearm in 9mm you would need to use not only a sound suppressor but also you would need to use a less energetic powder load in your 9mm cartridges so that the bullets themselves would travel at less than supersonic speeds. On the other hand, since .45 ACP is normally a subsonic cartridge to make a weapon firing .45 ACP truly silent all you'd need is a suppressor; you wouldn't need to fool around with the powder load in your cartridges.

If this is true, why does anyone bother with suppressed 9mm weapons at all? Neither 9mm nor .45 ACP will do well against armor, so that's not a reason, and the conventional wisdom is that .45 ACP is more likely to randomly incapacitate someone than 9mm. Is the only reason that people suppress 9mm NATO standardization, or is there an actual good reason to use suppressed 9mm over suppressed .45 ACP?

the only good argument that springs to mind is that if you go with 9mm subsonic, you don't have to buy whole new gun. attach a suppressor to your standard-issue Beretta, pop in a clip of subsonic, and voila--suppressed weapon. likewise, take off the suppressor and load a clip of normal rounds, and you've got a sidearm that can accept the standard ammo your organization uses. if you wanted to go with a .45 weapon, though, you'd have to get a different gun, and the suppressor you got for it wouldn't work on your Beretta even if you wanted to use it.

Not all subsonic 9x19mm loads are less energetic than average, it just means you have to go with a heavier bullet. For example, instead of a 115-grainer at 1200fps (368ft-lbs) you could go with a 147-grainer at 1020fps (340ft-lbs) -- and there's the added benefit that the heavier loads are more likely to penetrate the necessary 12", light and fast 9x19mm loads often lacking in that respect. AFAIK, all the common 147 grain loadings for the 9x19mm are subsonic when fired out of a 4" pistol barrel. The KE will be less than +P or +P+ loads, but terminal effect is not necessarily gimped: a quality 147gr JHP at 1000fps will reliably expand to 0.6+" and penetrate to 15+".

You have to make sure your ammo is subsonic with the .45 ACP as well. 185-grain +P loads break the sonic barrier handily, as do some 200-grain +P loads.

Really, the arguments are largely the same you get for 9x19mm vs. .45 ACP when sound suppression isn't involved.

no firearm is truly silent unless you can keep the slide from racking on a semiauto or the cylndar from rotating on a revolver. You might make the "firing" of the road silent but th slide racking makes noise. The SEALs/Special Forces have a special .45 that they can "lock down". When the pull the trigger, the slide doesnt move, it doesnt eject the spent round, nothing. And with the silencer it is the closest thing to truly silent. These are not your average .45 handguns but very expensive ~$5k handguns with special features.

Even at under 300m/s, a projectile large and fast enough to kill people at range is going to make noise. Plus a railgun isn't a firearm.

Maybe if you used electrical energy to launch an arrow-like projectile at 70-150m/s you'd get closer to "silent" but still have it be lethal. Of course, the advantages of that over an actual bow are pretty marginal.

I was sort of joking.

A video of an actual subsonic rail gun located at http://www.powerlabs.org/railgun.htm (15kJ power shot) shows that the capacitor discharge would produce auidable noise. However, I'm not sure how much was the noise was the capacitors discharging and how much it was the rails vaporizing, sending out a plume of plasma and turning the projectile into a brilliant tracer..

I think that the poit was the 9mm is the NATO standard and it the standard for many law enforcement agencies. If you can legally obtain a silencer without jumping through a lot of red tape then you probably work for an organization that issues a 9mm pistol manufactured by Baretta as its standard.