By Jeff Brown
Lately I have been working on a load for my .303 Pygmy (.303 British x 1.5 inches) that will produce field accuracy with a 180gr air cool wheel weight alloy (ACWW) and a muzzle velocity of 18-1900fps. The Pygmy has a case capacity similar to the 7.62X39mm so rather limited and to compound this situation and in order to produce the desired velocity in such a small case the pressures are likely to exceed the tensile strength of ACWW. In the past I have loaded the same bullet over a charge of Bench Mark, albeit with heat treated WW alloy, at the desired speed but such a hardened metal will not expand on game. The best way I deduced to reach the required velocity yet stay inside a pressure range suitable for acceptable accuracy with ACWW was to use a comparatively slow powder for a stubby little case. Bullet casters have reported very good results in the past burning a full case of VERY slow burning powder the likes of surplus .50 BMG propellent. The burn rate of the powder is so slow that there is physically no way to overload the cartridge and filling the case to the base of the neck then seating a suitable lead alloy bullet on top of it is the prescribed formula for a safe, modest pressure load. Looking over my stock of powders the slowest candidates on hand were IMR4064 (half canister given to me) and H4350 (AR2209 by ADI Australia). Both powders have a burn rate significantly slower than that of Benchmark however the challenge with the comparatively very slow H4350 was to get enough of this ‘coal’ into the little case to achieve the speed. 30gr of H4350 gives 1850fps but comes within 1/8th inch of the case mouth and when seating the soft ACWW to correct OAL on this charge the compression required was beginning to deform the bullet nose. Scratching my head for a solution I recalled my black powder cartridge rifle (BPCR) loading days and using a drop tube to squeeze the absolute maximum amount of black powder into a case. For the uninitiated, a drop tube is a length of tubing of a desired length down which a powder charged is trickled into the cartridge case at the bottom. The drop from height allows the powder to pack down tighter and thus allows for a larger charge to be loaded. My own drop tube is an aluminium arrow shaft approx. 2 feet long. Dribbling the charge down the tube into the Pygmy case packs the powder down approximately an additional 1/8 inch and sufficient to seat the bullet to the right depth in the neck without the need to greatly compress the charge and/or damage the bullet. I have been able to achieve 100% load density with a very slow powder in a tiny case producing workable field velocity at pressures that the relatively soft bullet metal will tolerate.
Below L-R: Drop tube with funnel set up on loading bench, cartridge case with drop tube in mouth, charge comparison L: drop tube, R: poured.
Lately I have been working on a load for my .303 Pygmy (.303 British x 1.5 inches) that will produce field accuracy with a 180gr air cool wheel weight alloy (ACWW) and a muzzle velocity of 18-1900fps. The Pygmy has a case capacity similar to the 7.62X39mm so rather limited and to compound this situation and in order to produce the desired velocity in such a small case the pressures are likely to exceed the tensile strength of ACWW. In the past I have loaded the same bullet over a charge of Bench Mark, albeit with heat treated WW alloy, at the desired speed but such a hardened metal will not expand on game. The best way I deduced to reach the required velocity yet stay inside a pressure range suitable for acceptable accuracy with ACWW was to use a comparatively slow powder for a stubby little case. Bullet casters have reported very good results in the past burning a full case of VERY slow burning powder the likes of surplus .50 BMG propellent. The burn rate of the powder is so slow that there is physically no way to overload the cartridge and filling the case to the base of the neck then seating a suitable lead alloy bullet on top of it is the prescribed formula for a safe, modest pressure load. Looking over my stock of powders the slowest candidates on hand were IMR4064 (half canister given to me) and H4350 (AR2209 by ADI Australia). Both powders have a burn rate significantly slower than that of Benchmark however the challenge with the comparatively very slow H4350 was to get enough of this ‘coal’ into the little case to achieve the speed. 30gr of H4350 gives 1850fps but comes within 1/8th inch of the case mouth and when seating the soft ACWW to correct OAL on this charge the compression required was beginning to deform the bullet nose. Scratching my head for a solution I recalled my black powder cartridge rifle (BPCR) loading days and using a drop tube to squeeze the absolute maximum amount of black powder into a case. For the uninitiated, a drop tube is a length of tubing of a desired length down which a powder charged is trickled into the cartridge case at the bottom. The drop from height allows the powder to pack down tighter and thus allows for a larger charge to be loaded. My own drop tube is an aluminium arrow shaft approx. 2 feet long. Dribbling the charge down the tube into the Pygmy case packs the powder down approximately an additional 1/8 inch and sufficient to seat the bullet to the right depth in the neck without the need to greatly compress the charge and/or damage the bullet. I have been able to achieve 100% load density with a very slow powder in a tiny case producing workable field velocity at pressures that the relatively soft bullet metal will tolerate.
Below L-R: Drop tube with funnel set up on loading bench, cartridge case with drop tube in mouth, charge comparison L: drop tube, R: poured.