For me it depends on what it is & what the manufacturers instructions are. Most pistols I run about 100 rounds of fmj & a couple magazines of whatever JHP ammunition I plan on using. My main purpose is to make sure everything works & the JHP ammunition I plan on using will feed.
When I bought a Kahr CM9 the manufacturers instructions said it needed a 200 round break in. I did what they said then tested the carry ammo I planned on using in it. The only malfunction I had was due to my thumb pushing down on the slide stop & keeping the slide from locking back. That things is small. Of course that happening touches on the other purpose of doing all of this. Before I carry a new gun I need to be familiar with all of it's controls, the ergonomics, etc.
When I bought a Kahr CM9 the manufacturers instructions said it needed a 200 round break in. I did what they said then tested the carry ammo I planned on using in it. The only malfunction I had was due to my thumb pushing down on the slide stop & keeping the slide from locking back. That things is small. Of course that happening touches on the other purpose of doing all of this. Before I carry a new gun I need to be familiar with all of it's controls, the ergonomics, etc.