9mm or 45ACP always works. Even 22lr will do.
I used to run the pin event at Blackwing with my B.I.L. He still does, I opted out as they kind of pissed me off.
We always liked to see folks using off the shelf, center-fire ammo of any caliber instead of handloaded bunny-farts as we tried to make the event use something more than point and shoot, square range skills.
Not always a success.
While the event is meant to be fun and relaxed (it really is) we viewed it as an opportunity to practice the basics. Target transitions from one side of the rack to the other, mandatory reloading, specific order of target engagement to force some brain activity etc.
If you've never been to one I suggest giving it a go. As I stated, it's meant to be fun and the only real stress is what the shooter brings with them to the firing line.
EDIT: Pin count will vary. Depends on the setup for that particular event. I don't recall ever having less than eight or nine.