Sorry I'm late to the thread, Dave.
The owner of the Venom tuned TX at the Boinger bash was BBS member, Snooper601/John, who's gun sported a left handed thumb hole stock, John won a Big FT event with this gun some time ago, it's also the first gun I ever hit the Quigley bucket with.
The Venom piston in this gun was running at MK1/MK2 stroke and had an alloy body, the total weight of the piston including bearings and seals was 180 gram.
There was another Venom tuned TX at another bash owned by Slinger69 which he'd just bought from AirArms David but we never opened that one up to take any measurements --- sorry.
All the best Mick