This is just a wierd idea, but : If shooting 100 projectiles in one frame is too much, pre-spawned projectiles isn’t good but you absolutely need to have 100 individual projectiles to be shot, how about changing your shoot mechanic so instead, when using the “shoot” button, it’s shooting 10 projectiles per frame for the next 10 frames? Or shoot 20 projectiles per frame for the next 5 frames?
5 frames isn’t that noticeable during 60+ fps gameplay (less than 10th of a second) and it’d give your “shotgun”-like shot a more realistic look and some variety since even with realistic shotguns not all bullets exit the gun at the exact same time.
If you want to counter this so bullets end up at the max bullet distance at the same time you could give the bullets that get spawned later a slightly higher speed (set bullet speed = normal bullet speed + small bonus speed depending how late that bullet got spawned) so they arrive at the max distance at the same time with the bullets that got shot on the first frame.