In short, an assault weapon is:
The 1990 law states:
"A semi-automatic shotgun with either a magazine capacity exceeding six rounds, a pistol grip, or a folding stock."
The 1996 AG Guideline states:
"a semi-automatic shotgun that has at least 2 of the following:
1. a folding or telescoping stock;
2. a pistol grip that protrudes conspicuously beneath the action of the weapon;
3. a fixed magazine capacity in excess of 5 rounds; and
4. an ability to accept a detachable magazine."
The law is the LAW, and the guideline is a GUIDELINE. In this instance, the guideline contradicts what the law says. AFAIK, no one has been prosecuted for violating a guideline.