Well I like "Der Schprocket" as in "time for schprockets to dance!" But to tell you the truth, the damn thing reminds me of a "hogie."
The French refer to their FAMAS G2 rifles as le clairon, *the bugle* due to its short appearance and musicle instrument-like sight mount/carry handle.
Russian troops in Chechnya and elsewhere refer to the lengthy SVD Dragunov sniper's rifle as *the oar* and to some British troops still claim their SA80/L85A2 bullpup rifles as *The Enfield* or *Tin Nelly.* I hope the XM-8 manages a little better than any of those. *Eightball* seems an unfortunate but likely possibility.