Location: Virginia, just outside of Washington D.C.
Posts: 3,788
That does look like fun and the ad is probalby right about it being VERY loud. But at only 18 inches I'm sure some law types are licking their chops with ruler in hand. He ought to make them 18 1/4 or 18 1/2 inches long so no overzealous type comes after you.
For $250 you can probably get a used Mossberg 835, which is overbored to 10ga dimensions. Cut that to 18.5" and you'll have something pretty well suited.
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