For those that might be interested, here are a couple of pics of the Lancaster/Beesley mainspring-cocking limb. The broken spring pictured is from a body action "0" serial numbered Lancaster circa 1896. It is the original, factory spring. I believe this to be the change in design that was filed for in 1894, patent number 7242.
The other spring pictured is an unfinished-unfitted spring that would be found on an earlier patent (#425 of 1884) Lancaster gun. This spring was found in an old parts bin :-) too bad it couldn't be used on my job.
The replacement for the broken spring took approximately 11 hours to make, completely by hand from a small block of steel.
Broken spring...
Parts bin early type Lancaster mainspring...