(I did this with the shotgun, but u can do it with any weapon u want)
First open up DotHalo open up the map u want then scroll down to weapons tag and select the shotgun. now go to the dependencies tag and change the
proj - objects\weapons\rifle\shotgun\projectiles\shotgun_ bullet to
proj - objects\weapons\grenade\plasma_grenade\plasma_gren ade now save changes and go up to the proj (projectile) tag and select plasma gernade and change inital projectile speed and final projectile speed to 400 (u can make it wutever speed u want, 400 is jus what i did) now save changes and close DotHalo. Then open up H2X then open up the map u want then scroll down to thw weap tag and select the shotgun then open up the meta editor and go over to the Projectile option on the left hand side and change bullets per shot to 50 ( u can change it to wutever u want but at 50 it lags when u shoot it with automatic fire but u can do wutever u want) then press the blue save changes then the white save changes.
Now jus resign, ftp and there u go u now hav a plasma nuke