You are unable to tweak the bleeding chance for projectiles (i.e. bullets, throwing darts, icicles, etc.) unless they're spawned from a held item (via adding a bleeding chance for that item), and even then, hitting an entity with the item will cause bleeding, even if realistically it doesn't make sense.

It would be nice if you could change the bleeding chance for projectiles, or alternatively disable bleeding chance for hitting a mob with the item itself (although it wouldn't work to well for mob-exclusive projectiles)