What is the difference between a low velocity and high velocity gun?

I don't know if this answer will satisfy you, but there is not much difference. Higher velocity is higher speed. But 1100 feet per second (appx) is the speed of sound, and guns that have a "subsonic" bullet are much quieter than guns whose bullets break the sound barrier at just a slightly higher velocity.

Answer:

To truly discuss firearm velocity issues would require the writing of a book, but it suffices to say that one of the usual differences is chamber pressures and barrel life. The super high velocity calibers such as the 220 Swift generate so much heat that the rifling can be worn from the barrel in as little as 3000 rounds, whereas a lower velocity round such as a 30.06 barrel has a longer barrel life.

The next obvious difference is trajectory. As it takes a certain velocity to break from the earth's gravity, the same holds true with bullets. The faster it is traveling to longer it takes for gravity to lower it from its aimed point.

Last, but not least. Hollow point bullets require higher velocities to properly expand and release more energy into it's intended target. This becomes a real issue when fired from a handgun.