To explain very basically. You'll need external programs to achieve PartMerging, like I did with the Juggernaut, Oneshot, Vulcan Fury and Blackhole. Simply adding sniper barrels to revolver barrels is not gonna cut it. PartMerging is prob's one of the most advanced Custom Weapons/Items forging skills out for BLCC.
As for if the Hellfire being made by it, I dunno. I'd have to check its individual .upk file to see if it did, but from what I can see from the itemcard. It didn't. Whatever he/she did to make this weapon, it turned out to be a heckjob.
Could you send me the Hellfire's' .upk file?