I am investigating ways to make a "40mm Buckshot" munition (there was a real-life version before the M79 was made effectively obsolete by the M203). I tried just altering the projectile to use the buckshot, but then I ran into the problem of impact data; these little pellets of buckshot were kicking up huge clods of dirt with every shot since the default impact data set in the WEAP form is for frag explosions.

So I switch it to use a fake explosion to override the impact data set. That problem's fixed.

But now I have another problem... I have to put a monstrously huge damage modifier ammo effect onto it, since the WEAP form's damage value is just 2 on the rifle and launcher, and a problematic non-identical 5 on Mercy (IIRC, don't have the GECK open now).

I got to thinking... make small-radius fake explosions to deal the damage.

However, in testing another thing I'm working on (coins scattering everywhere with Coinshot, which uses placed impact object fake explosions), I discovered that fake explosions apparently don't apply damage... or at least the dummy fake explosion included in the archives doesn't...

Any tips on how to make fake invisible explosions inflict damage? This would also allow me to disable Hitscan on the coinshot so you can see the coins in flight as well, if it works (due to non-hitscan projectiles inflicting no direct damage if set to explode on impact).

Explosions only apply damage to anyone with their actor node in the explosion radius, and actor nodes are usually at their feet, so it doesn't really work. Also, if you put an explosion on a Missile-type projectile then the actual projectile itself does no damage (outside of VATS), just the explosion.
It's a very annoying problem.

Well, you definitely need to be using a projectile with no explosion set. The problem is that Impact Data Set is a property of the weapon itself. So, you'd basically need to change the impact data set somehow. I'm not sure if there's a way to change this via script, but if there is, there are ways to determine what ammo you have loaded and to do stuff to your weapon in that case.