No ‘lightweight’
My son recently began clay shooting with 21g 12-bore cartridges, mainly because of their lighter recoil. I mentioned to friends how well these cartridges have performed and was told lighter shot load cartridges often ‘punch above their weight’. Is this the case? I’m considering using the cartridges myself given their performance, reduced recoil and lower cost. Are lighter shot loads the way to go?
Richard says: You have discovered what many did when 21g cartridges were first introduced. Lighter shot loads pattern more tightly than heavier shot loads when shot size and quality, wad type and velocity are the same and fired from the same gun and choke. There are several reasons why this is so, but the key factor is the lower sectional density of the shot charge. Put simply, the height of the total shot charge in the cartridges, and bore of the gun, is shorter than of a heavier shot charge. This results in less crushing of the lower layers of pellets in the shot charge under the heavy acceleration forces upon cartridge ignition.
The huge set-back forces generated always crush and deform lead pellets to some extent, with lower layers of pellets subjected to increased crushing forces.
That is why premium-grade competition cartridges are loaded with harder lead shot so that pellet deformation is reduced and pattern density increased. Less deformed lead shot pellets will therefore fly more true, being less prone to extra deflection from true flight when forcing their way forward against air pressure. This is the key reason that similar-quality cartridges of lighter shot load in the same bore produce relatively higher pattern percentages through the same gun and choke than heavier shot loads.
The actual number of pellets in your pattern is unlikely to exceed that of a decent 28g cartridge as there will be 25% less shot to begin with. What actually happens is that when pellet hardness and velocity are similar, the 21g cartridge will typically put a higher percentage of its shot load inside a 30in circle at 40 yards. Typically this will result in a 10% (and sometimes more) increase in pellets in the pattern. This equates to achieving a full-choke pattern (70%) from a 1/2-choke (60%) gun/choke.
The result is that 21g cartridges can make up for some of their reduced pellet charge and therefore perform rather better than might be expected. They will not match premium cartridges, but they will break all but the longest-range, edge-on targets.