I seem to be having issues with hp_firepoints in my gun models.

The way I set up a weapon to get ingame is like this.
I position the model on the axis so that the axis is where the knuckle of the first finger would be when holding the gun.
I create a triangle mesh, place it at the front of the gun barrel, name it hp_fire, and hide it.

Upon export, the gun is properly held, but the muzzleflash and ammo come from the axis as well, instead of the hp_firepoint.

Milkshape 3D appears to be incapable of handling nulls, so I figured I'd just use meshes.

Can anyone tell me what is wrong?

Your problem is that you're hiding the msh. What I would suggest doing is giving your hp a transparent texture and then hexing trans onto it when you export. If that dosn't work, than you have to do it by way of putting your model into XSI and then using mshex.

Well, it still doesn't work even if I don't hide the mesh.

EDIT: the mesh doesn't appear ingame, but the firepoint is still incorrectly placed.