Sometimes we hear from some hunters that their rifle is excellent with a type of powder or cartridge, but not with others, that it shoots well with big lead and not with small shots, with strong charges and not with light charges, or other way around. These hunters, getting excited with speeches barroom, talk about wonder weapons that produce shot patterns of the same extent in the short and long-distance shooting, or shot patterns with peripheral shots that are equal in ability to penetrate than the central ones.
Those statements hide many inaccuracies and erroneous assessments, with unlikely attempt to explain the phenomenon of variability of the performance of weapons and shot cartridges, a phenomenon observable by everyone engages the hunt or the skeet shooting. Someone, instead, blames the gun or the ammunition for all the misfires, or enhance the quality at every success, not caring so to deepen that the effectiveness of the shot not only depends on the characteristics of these instruments, but of many other variables.
It is known that the outcome of the shot depends not only on the characteristics of the gun or the cartridge, but also on the environmental and climatic conditions existing at the place of hunting. We can now speak of “temperament” of shotguns, because each weapon has its own temperament, manifested by the degree of compatibility with specific cartridges producing a high or a low value of velocity and pressure, or by the ability to produce pronounced or contained dispersions of shot. The weapons that have barrels of good length and small diameter can give acceptable ballistic results also firing cartridges with speed and pressure rather low, contrary to the weapons with barrels shorter and wider, which improves performance with powerful ammunition.
In the ammunition, on the pressure, on the speed and on the dispersion do not affect only the meteorological factors, but also the diameter of the cartridge chamber and of the bore, the extent of the choke and the angle of the barrel throat, the length and thickness of the tubes, and, minimally, the elasticity of the steel with which the barrels have been built. Therefore, the compatibility of weapons and ammunition is very important, although it can not compensate for an excessive sensitivity of the powder to the intense cold or to the environmental damp.
In fact, the ballistic performance of weapon and cartridge can not have “related” value respect to different “external” parameters to the system, because it also depends a lot on the atmospheric conditions existing in the place. Many hunters like to divide the cartridges in winter cartridges and summer cartridges.
A difference of atmospheric humidity of 10% can produce a variation of the initial velocity of lead of about 5 m/s with a single base powders, 3 m/s with a double base powders containing nitroglycerin. A difference of 1° C in the outside temperature, can cause a change in pressure in the barrel of about 3 bar. If this phenomenon occurs in a very short time, making unserviceable a cartridge that a few hours before killed a game, almost always the cause is found in the cartridge itself, and not in the atmospheric influence in so little time. In some areas of Italy, when there is an atmospheric change, the cartridges may lose all or part of their efficacy, without the powder has had time to warn the external atmospheric mutation and to change its temperature inside of the cartridge case, or to absorb moisture through the plastic tube.
So when a good cartridge loses its effectiveness, it does it in a period of time long enough; if the phenomenon is realized in a short time, we can not speak of a good cartridge but of a munition that has some defect.