I cant help on that one mate. I have one with an old cut down Venom spring doing about 11.7 in .177 and another that came to me with a standard brand new spring also in .177 that I think is just under 11. I would add that both have gone over to ptfe however.
If you still have the lug attachment I wouldnt scrap the old cylinder by the way. I am sure there is someone out there with the skill to weld it back on stronger than it was originally?
Dave