Generally speaking, ammunition that hits its target is destroyed or rendered useless, while ammunition that misses has a 50% chance of being destroyed or lost.
Does this rule apply to firearm ammunition?
Does this rule also apply to magical ammunition?
Unlike other types of ammunition, firearm ammunition is destroyed when it is used, and has no chance of being retrieved on a miss. No part of a cartridge can be reused to create new cartridges.
That answers one of my questions.
Go throw a tiny marble, or miniature black dice out into the middle of a lawn, preferably using a sling shot. Go try to find it. Indoors? perhaps find a large messy public area and do the same thing. Of course if you miss indoors, the bullet is going to hit "something", most likely the wall, and that would destroy the bullet.
Now, even if you could find the ammunition, how long do you think it would take to find just 1 bullet? It is a big difference than trying to find a two-three foot long arrow, or even a golf ball sized sling stone.
You can't recover ammunition, even magical. It clearly says in the rule it is destoryed, it doesn't differentiate between magical and non-magical. If you've never shot a gun, it doesn't matter what kind of ammunition it is, you're not going to recover a usable part of the lead bullet. If you're talking about modern style ammunition you can recover the cases from spent round, but not the lead. Most firearms in pathfinder are musket like and fire a ball, which would be destroyed upon impacting anything (which it eventually will).