I agree with most said above, the old english system is traditional and convenient to use if you are familiar with it. I'm from south america, and we (as ALL the rest of the world, and most major industrial U.S. manufacturers of everything but guns, U.S. millitary, etc...) was raised on the metric/international system, but notheless find it easy to use the US system (actually most everything made today with numeric tools can "tranlate" automatically any unit of measure). Mal H, with due respect, you are a bit too focussed on US cartridges, remember that many "traditional" loadings of continental cartridges were originally in grams (9mm Luger: 8 gr. = 124 grains, 8mm Mauser: 10 gr. = 154 grains, and so on...), what happened afterwards is that in recent times most of private firearms experimentation,ownership,tinkering, new shooting sports, etc. was carried out in USA, thus commercial suppliers, manufacturers, loading books, and most data available to the private shooter is according to the standards of this country. I´m sure that eventually the metric/international system will replace the english one in USA in everyday life (most people just don't realize that factories are changing now), but the question is when.