system
Given the following post, respond as if you're commenting on Reddit:
human
When does a bullet reach its maximum velocity?

I was wasting my time on youtube watching gun videos and this got me thinking. The bullet has to reach Vmax from standstill in some time, then is slows down due to air drag. It should be somewhere in the barrell, but is there a way to know when and where?
Also is this related to the force the gun kicks back with?
gpt
Probably right as it leaves the barrel. For many cartridges, firing the same bullet from a longer barrel will result in higher velocity because it doesn't "waste" as much of the gas expansion.  Imagine a very snub nosed revolver: there's a huge flash of fire out the barrel *around* the bullet, and all that gas expansion is "wasted" (it doesn't push the bullet any more)