As an example, I created a Projectile Object Channel which is blocking by default but the spheres are Projectile Object Type and ignore Object Responses of that type:
So the projectiles can bounce off everything bar themselves:
https://i.gyazo.com/1cc09a3d16637a2b…f6b6cb36ce.mp4
Do note that you can adjust this dynamically, too - lets say 1s after spawning the bolts can block each other again if necessary for some mid-air collision shenanigans.