You can set up meshes from projectiles pack, like bullets, in your realistic blueprint weapons. But I think, if you want to add support of blueprints in realistic blueprint weapons pack, you should rewrite a lot of blueprint code in it. Or you should contact with developer of this pack and ask him to add a support of blueprints.
Projectiles pack implements projectiles blueprints in a way, when you just need to spawn projectile(look at first person character blueprint for example) to make things work. It means that all projectile logic, like line trace for target and applying damage are inside it and you don’t need to implement this logic again in your weapons. But you can change this approach if you want, by adapting code from different packs on your own needs by yourself(because different packs may be incompatible with others, or implements the same functionality).