There are many Fox guns that letter as to barrel length but the tubes don't touch. I have an XE sixteen that fits that criteria myself:
I work on a lot of Fox's and I have still to see one with the space you pictured.....the ones I've worked on don't have enough space worth talking about......same with other brands as well.....
I don't think there are
many out there, but probably are some.....?.......
What I see look like this 1909 A Grade 12 that I did a refinish on recently:
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Besides customer guns, I personally own five Philly Fox's, 12's, 16's, 20's and they all have muzzle tube spacing like my 20 bore pictured below, basically touching.........all are lettered with Callahan and all are uncut with the original factory M/F choke configurations:
