Dr. Marneaus
.270 WIN
This is where the shockwave is in its' own little area.
And the area leaves very little with no room to wiggle.
If it ever had a BUTTSTOCK, then it can't be shortened to below 18 inches, else it would turn it into an SBS. Barrel length is in the federal regs.
As for pistol gripped shotguns, it could depend on how Mossberg recorded the listing they have to provide the feds, and if you bought it new, could also depend on how the FFL transferred it to you.
On the 4473, the 3 choices are long gun, handgun and receiver/other.
In the case of the shockwave, it should be listed as other on the background check and also in the FFL's acquisition and disposition book because it is neither a long gun (shoulder fired), a handgun (pistol--also nothing above .500" caliber are allowed in handguns) and the only thing that would fit the FIREARM is "other".
So, there's really a pretty narrow path that the shockwaves pass legal scrutiny. It's not just whether the gun only had a pistol grip or not.
Hmmm, my recollection was that even before they were factory made options, that anything that came from the factory as a PGO firearm, remington or mossberg, regardless of barrel length, was sold as being PGO, never having had a stock, and therefore was not a shotgun, and these were the ones you could convert yourself before the factory started producing them.