T3PRanch says that: .389" is the thickness of the magazine
I have tried to get that info from the FX site and even from the US distributors to no avail. Given this .389" max, looks like I've got 4 slug possibilities from NSA:
34.7 gr. w/0.334" O.A.L.
36.0 gr. w/0.323 O.A.L.
39.0 gr. w/0.351 O.A.L.
44.0 gr. w/0.386 O.A.L (this one might be cutting it too close)
Thanks to all who replied. After I get the Warcat I'll let you know how these do-