Martini-Metford
In 1899, the Mark I, .303 Ball Cartridge was approved, using 71.5 grains of a pelletised Black Powder, with a 215 grain cupro-nickel bullet. The Mark II Cordite round was approved in 1893. The Cordite Mark II was more stable than the Mark I round, but generated greater heat, giving more velocity but increased barrel wear.
The Metford rifling was designed for black powder loads. When smokeless powder began to be used in the .303, the Metford rifling was not suitable, and eroded fairly quick for Military usage. The rifling was then changed to the Enfield type rifling, which did not erode so fast using smokeless powder. Metford rifling is seven grooves of .004 inch, while Enfield rifling is five grooves of .005 inch.
The Metford type rifling had shallow, rounded grooves, while the Enfield type rifling had deeper, squared off type grooves. Metford rifling was designed for better cleaning of barrels that used Black Powder propellant.
Light starting loads of a medium burning powder should be all right for your purposes, but a cast lead bullet should really be good. Be sure to choose a heavier bullet, with a more rounded nose, as that is what the rifling was designed for.
Check the Knox form on the barrel. Many of these Martini rifles were rebarreled with Enfield barrels---they have a "E" stamped on the flat of the Knox form.
Personally, if I were going to shoot this rifle, I would use lighter loads of medium burning smokeless powder, with a 180 to 215 grain bullet, either jacketed or a 1/10 Lead mixture. The problem with Black Powder is cleaning the barrel, and in the Martini, that must be done from the muzzle. If you do clean from the muzzle, I would use a bore guide, so that the rod does not wear on the rifling.
For the amount of firing you are likely to do with this rifle, I would not worry too much about wearing out the barrel. I would be more concerned with cleaning the barrel, so that it does not rust, pit, or corrode. The Metford rifling was designed for a service life of 5000 to 6000 rounds before coming unusable, as long as it was cleaned properly and promptly.
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