I was wondering why it that most standard 9mm and .40 ammo is supersonic but standard .45 ammo is subsonic... I just can't wrap my head around the concept. Anyone know the reason why?

The .45 ACP is a heavier bullet than the other two and it doesn't carry much more powder in the shell. The speed of sound is 1080 ft/sec at sea level. .45 ACP can be loaded to +P+ with a 185 gr. bullet to muzzle velocities in excess of 1200 ft/sec. Not all .45 ACP loads are subsonic.

It's just the original design of the .45 ACP round. The round was designed a long time ago, and it was designed to be a powerhouse. That's why it's slow in comparison to the other common pistol rounds out there.

Think of it like this... Bullet velocity OVER the speed of sound is roughly 1100 feet per second (750 mph) making it SUPER sonic. .45 ACP travels at about 850-900 feet per second. Now, if you take all three rounds into equal material, you will see that speed does not always equate to overall damage... Hence the reason the .45ACP was handed down from John Browning himself as THE bullet of choice. Subsonic AND packs a hell of a whallop. JD

JD has a good point. Would you rather be hit by a fully loaded Mack truck at 35, or a Honda CBR at 60?

I understand the physics. But I don't understand the whole '185 gr. bullet'... is that indicative of the bullet mass? How do you determine the approximate powder load for different ammo?

"There are 252.7 grains in one cubic inch of water. To calculate the total bullet weight in grains, the bullet volume, in cubic inches, is multiplied by the specific gravity value, and then by 252.7. The product is bullet weight in grains. " Lilja Rifles has a great page dedicated to this study and understanding of what and how. It's very informative. As to determining what load to use behind what bullet, that is WELL beyond my meager understanding, that is why I use reloading manuals. JD

Yes, 185 grain is the bullet weight. There are tables for handloading. The indicate what bullet weight and what amount of which type of powder to use to get a given muzzle energy and velocity.

Heavy/slow vs light/fast is kind of like torque vs horsepower. They both do work but in different ways.

A milisecond between when the bullet hits home and if placed where it should be a milisecond from death. Might just be me but this question is a moot point unless your a supper ninja that moves so fast where supper sonic and sub sonic matters. Yep the 45 round is slower but unless you can slow time it will end up exactly where indtend a milisecond latter.

indeed but im pretty sure your chances of surviving the CBR collisision are significantly higher than the mack truck even if they are both pretty slim. thats why the .40 is such a good middle ground between the 9mm and the .45. 9mm is the CBR, .45 is the mack truck...that makes the .40 an GMC sonoma