Dwestfall:
The longest extension for an 18.5" barrel would be a +4, which will give you 7 in the mag, 1 in the chamber, and one on the carrier, for a grand total of 9 rounds. I know some people who shoot Bennilli's with mag tubes which extend past the muzzle, with no ill effects. Hope this helps.
p1445
Oh yea,
From my understanding of the law(taken from the batf site), the largest mag capacity on a post ban, with a pistol grip is 5. So you could have 5 in the mag, 1 in the chamber, and 1 on the carrier, for a total of 7.
[This message has been edited by p1445 (edited December 26, 1999).]