Collision channels are usually sufficient, but if the shooter and the target are both on the same collision channel then the projectile could collide with the person/weapon that fired it. To avoid something like this, you can try using the “Ignore Actor When Moving” node. I’ve done this in C++ and it works but I haven’t tried it in blueprints. Just call that, once with the character and once with the weapon (if necessary). Note you can also turn the ignore off, so if you want it to be able to hit its owner but still fire properly then you can call that node again after a given distance/delay.
There is also a system that lets you ignore actors by flag but I’ve never been able to get that to work.