I have a Burris 'Signature' in 3-9X and the tube length, not including bell ends - just the mounting portion of the tube - is 6" from end to end. (I'm only guessing the tube of the Signatures and FFIIs would be the same or very close.) I have a couple of Fullfield IIs but not in 3-9
Edit: Ooops, never mind, FDT's got ya covered! Scooped me by seconds!