As a gunsmith I can work happily in metric, Imperial, or a combination of both, but I tend to do all my design drawings in metric. As for the Enfield Inch; it is not worth worrying about as the difference is way smaller than any normal manufacturing tolerance. Curiously, the US, which is the last bastion of Imperial measurements, has only one official system of weights and measures, which is the Metric system and was adopted by Congress in the 1860's (probably the reason they don't use it much!). I have a 1991 GMC pickup which is made with a combination of metric and Imperial measurements!