What's a quieter cartridge?

you would have to have a dB meter to see.

I'd bet lunch neither you mention would be signifigantly louder or quieter than the other.... both will wake the dead, cause hearing loss is a person persist in exposure and will wake the dead if shot indoors

Shorter? Just because the case is shorter won't mean much. The powder formula and pressure it creates and barrel length are all part of the sonic signature of a cartridge

This is actually a difficult question, mostly because of the age of the .45acp and the loadings available for it.

In its native configuration, the .45acp fires a 230 grain projectile at around 850-950 feet per second. That is below the speed of sound. So all you have to contend with is the actual muzzle blast of the shot.

However, there are many combat loads, especially in the ligher bullet weights and +p pressures, which raise the velocity to around 1150 fps, which is supersonic. So now you have a larger muzzle blast AND the supersonic "crack" to deal with.

The .45gap, with its shorter casing and higher pressures, behaves similarly to the .45acp +p, although the numbers are still a little fuzzy depending upon where you get them. The 185 JHP in the gap comes in right AT the speed of sound, which is 1100 fps. The 230 grain .45gap is slower.

Because the ballistics are similar, the sound will be similar. Length of shell casing has very little to do with it.

But the loadings which are supersonic, in EITHER cartridge, will be significantly louder.

Doesn't matter. It's like asking what's wetter, the ocean or a lake?

In reality (most times) the lake is, because saltwater has a higher amount of disolved solids than fresh water. In actuality you would never see a difference. The same with those 2 handgun rounds, you would need equipment to tell the difference. And that's assuming they're both being fired out of the same type of handgun with the same barrel length. Any deviation between the 2 would marginally affect the volume of the discharge.

45GAP would be louder. Cartridge length has nothing to do with it. Case pressure however, does. The Gap is a high pressure cartridge. They are both loud, and I am sure the difference is negligible.

45 ACP is lower pressure, so marginally quieter, however you can't tell unless you're shoot them fro ma rifle... with a 25" barrel. they also don't make 45 acp/45 gap rifles with a 25" barrel.

Pretty sure the human ear couldn't detect the difference.

Indoors they'd both be equally loud.

You would not hear the difference.