I went to the ATF sight and read about the NFA and title 2 and the AOW rules. What I get out of it is that at production and importation this type of weapon had a pistol grip on it and would be considered a "smooth bore pistol, pump operated" or "AOW, pump operated". Barrel length and overall length doesn't matter at this point. With the 18.5" barrel I can put a shoulder stock on the weapon and it would be a legal shotgun. Put a shoulder stock on a gun with a 14.5" barrel and it would cost me $200. But as a pistol, the barrel can be shortened as long as it has never been a shotgun? So if I wanted to, I could cut the barrel, but would need to dispose of the shoulder stock?