The word is “cramp”. Unfortunately, I have no idea what it does. Nor have I seen a Lancaster in person with this feature. What’s the address on the barrels? 151 New Bond?
Cramping in the gunmaking term would normally mean a device the restricts movement, etc. The mainspring on Lancaster is long and flat. It requires no cramping (squeezing) to remove from the action, when the barrels are removed from the action, the mainspring is at rest.
Im not sure what this feature actually does🤷🏽‍♂️.