I wonder if in many ways there is a question of how well used the rifles are: I suspect that the older conversions were often owned by people who really used them i.e. they are well run in and are consequently smoother compared to a lot of the later conversions which if the sales section is anything to go by, are sold all too soon after completion and have not been given a chance to adequately run in.

There is as Nick points out perhaps a changing trend in tuning for faster lock times rather than simply a smooth delivery?

Talking of tuning greats, lets not forget Mr innovation - John Bowkett.