http://www.ebay.com/itm/VINTAGE-BESSON- ... 7675.l2557
Photos not the very best, yet it may be seen that the extra loops attached to the first two piston casings reveal a compensator.
The oddity of this design is the 3rd loop passing through the 3rd before entering the 1st valve.
The achievement of a hand rest might be the official reason behind this design. My suspicion is that the real reason was about circumventing the Blaikley patent then owned by Boosey.
Klaus