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"Nitro-for-black" loads are those which use a nitro powder to give the same ballistics as the original black powder 'factory load', at the same or less pressure. For example: in the .577 x 3-inch cartridge, the original BP load consists of a 540gr bullet over 165gr black powder, for 1650 fps at 10 tons pressure. The "nitro-for-black" load usually had a 650gr bullet loaded over 65gr cordite for the same 1650fps, at 9 or 10 tons pressure, and could be safely substituted in any BP-proved rifle. The full nitro-express load, on the other hand, sent off a 750gr bullet just over 2000 fps at perhaps 14 tons, and could not be safely discharged in a BP-proved firearm. |