Dating to 1888, the 303 British was originally loaded with blackpowder and a round-nosed bullet of 215 grains at about 1850 fps, which was substantial velocity for the era and for any blackpowder chambering. This was nothing more than a stopgap measure as Great Britain already then knew it would be using smokeless as soon as it could develop a satisfactory smokeless-propellant formula. That happened soon enough with the original, high nitroglycerin (NG), version of Cordite. But, this was soon found to generate extremely rapid bore damage, so the original formula was replaced with a version having far less NG and a substantial percentage of nitrocellulose (NC). Barrel life was far more satisfactory with this version of Cordite and performance was just as good. With the adoption of smokeless, performance was improved significantly, first with the original round-nose bullet (about 2100 fps) and later with a 174-grain spitzer (2440 fps). Few folks realize how Cordite was loaded in bottlenecked rifle cartridges. This required a unique production process. Before necking-down otherwise finished and primed cases a bundle of a specific number of propellant cords of specific diameter and length was inserted into the case. The case was then necked down and the bullet was inserted. While odd by modern standards, this was actually a very good method for loading ammunition with an efficient propellant for that era. Cordite allowed the 303 to offer impressive performance from a relatively small case with perfectly normal Military battle-rifle pressure, for that era. Cordite had many advantages for Military use and remained in the arsenal as a propellant for cartridges of various types and as a solid-rocket-motor propellant for many decades. While little known by today’s shooters, the 303 remains one of the all-time great battle-rifle chamberings and a perfectly respectable round for hunting most big-game species worldwide. I would like to know where the unusual bore size came from. Usually, in that era, where the imperial measurement system still held sway, bores were measured in calibers (1/100-inch, by definition), e.g., 45-caliber (45/100-inch) using a bullet of 0.458-inch to fit the 0458-inch groove of a barrel with a 0.45-inch bore. For this reason, the 0.303-inch and 0.312-inch bore and groove dimensions of the 303 seems odd.