You....could also probably commission a professional 3d artist that understands the craft to produce a good unique nail shotgun design. Weapon models aren't the hardest asset to produce, the weird parts are just the MD3 tags and the "hand" (which is an animated tag for 7 frames)
The OA model is quite trash, I'd advise to not bother with it. It's a hasty byproduct of entitled release pressure that exists more to end warning messages. I haven't even started my reboot's nailgun model yet and i'm still going with my blue notUnreal crystal motif.
(small fun fact: the earliest Q3 1.25 point release beta patch contains code for the chaingun/prox/nailgun, leaking Team Arena functionality in a way, a few months early..)
Edited 13.08 minutes after the original posting.
That's not what I meant at all...