Correct me if I am wrong, (and I often am), but I thought we were talking about 'run-of-the-mill', out the box models not tuned rifles.
If that is the case I nominate the prototype Omega with the adjustable gas ram. I, and several people who have shot it, cannot understand why Webley never put it into production. Perhaps it had something to do with patents or the fact there was no safety catch fitted for the U.S. market.
ATB
Ian