OK- I'm getting confused now. Is the "S.C." stamped on the barrel not indicative of a shortened "Lead" or "forcing cone" in response to change in bullet design? After reading this thread I spent an hour scanning all the usual references and this appears o be what is implied although I couldn't find any statement of exactly when it was first applied to SMLE barrels. Many references to accuracy experiments (in part pre MkIII) where a shortened lead was tested and, generally, found beneficial. I think jargon is starting to cause problems here?

Ridolpho