Oh, and here are the source images (that's almost a pun, since these were ripped from gmod rather than the real game.)
http://filesmelt.com/Filehosting2/downl ... ceimgs.zip
UBER late update, but here are some (rough) plasma grenade sprites based on the mortar in Duke Nukem.
They need the hand without a grenade part, but the main thing only needs some sequentially aligned duplicates aside from that. I'd look at the powerslave grenade for that.
Also, I suppose it could be a bio-amp or psi-amp or geo-amp or whatever amp someone might need.
I will state, ONCE MORE, if you want to use the grenade, download the zip, it has the mortar projectile and the properly sized grenade. Look to the doom-handed powerslave grenade for supplemental hands.