LGV - The AGW "Simple tune" doesn't work for me

[Benelli B76]

Are you sure you're talking about the break barrel LGV or is it the underlever LGU?

AFAIK
LGU compression tube with TP length of 6 mm:
5,5 fpe "F"-version: dia 2,6 mm
12 fpe full power version: dia 3,2 mm. You may go to 3,4 mm.
17 fpe FAC-version: dia 3,5 mm

Sorry, you are correct, the guys reminded me it was an LGU underlever.

Baz