The way you are doing it will work, but will quickly make your events unreadable. If you are only going to have two bullet types, this may be fine. If you add any more, it won't.
If you have a license, families would really be the best way to do this. Add all the bullet objects to a family and create a family level event for these collisions.
If you are using the free version, families are not available but there is still an easy way to have this collision event work for all your bullet types. Just use the same object with different animations for your bullets. So, instead of having a Cannon Ball object and a Fire Ball object, you would have a Bullet object with a Cannon Ball animation and a Fire Ball animation.