The creation of the first tranche of pattern data for the 2½” Eley “Trap” cartridge last weekend offers the possibility of a direct comparison between the behaviour of 2½” and 3″ cartridges which are essentially identical.
Allowing for the fact that differences in case capacity require either a different powder, or a different quantity of identical powder, the two versions of the “Trap” cartridge appear to be of common construction: there is no difference in wad, shot size, shot composition or crimp. We assume that the primers are also identical.
Thus, provided we compare the cartridges’ performance by percentage and not by absolute pellet counts, we can determine whether the simple fact of increasing the height of the shot column improves or degrades performance.
In fact, in the case of the Eley “Trap” brand, there is little difference.
The data collected at the time of writing gives a 42.5% average performance for the 2½” version of the cartridge fired through the 0.015″ choke of our test gun at 40 yards, compared with a 42.0% average for the 3″ version. The 0.020″ choke produces average pattern densities of 47.0% and 46.0% for 2½” and 3″ shells, respectively.
The SmallBoreShotguns team have not yet collected sufficient data to draw a firm conclusion for all chokings and distances, but thus far, we can say that if a longer shot column does significantly damage performance, it is not (yet) demonstrated by the Eley “Trap” loadings. In fact, the loss of performance in the 3″ cartridge is so slight that it will easily be outweighed by the greater number of pellets in the case, as the absolute pellet counts presented in the data clearly show.
We do not consider the Eley “Fourlong” (12½g / #7) and “Extralong” (18g / #7) to be equivalent-except-for-case-length: the former has a fold crimp; the latter a rolled turnover crimp.