Shot Distortion


I’ve been reviewing the articles on shot shells in this blog and various magazines. The consensus is that magnum shot is better because it is harder and there will be few flyers because they won’t go out of round on their trip down the barrel often rubbing the sides of the barrel and choke. However, there is another argument, especially when there is a concern of using steel shot that will scratch the barrel, that the shot rides all the way down the barrel inside the wad, so the shot never even touches the barrel. If it never touches the barrel, why do you need antimony? Will high antimony shot do a better job of breaking clays? Thanks for your thoughts.

Annapolis, MD


The shot does not entirely stay within the shotcup on the trip down the barrel. It is inside the cup at the start, but as it progresses down the barrel, the shot has built up inertia, while the shot cup develops friction against the barrel walls and slows down slightly. That can release some of the shot from the cup. It really depends on the exact load as to whether or not this happens.

One thing that does always happen is “setback”. Setback occurs when the primer ignites the powder and chamber pressure suddenly drives the shot and wad forward. The pressure push is from the back of the shotcup. The column of shot within the wad can be fairly tall in a heavy load or in a subgauge. The shot at the rear of the cup is pushed forward rapidly, while the shot at the front of the cup wants to stay where it is due to inertia. This puts pressure on the shot at the rear of the cup and can squash it slightly. This is setback. The longer the shot column, the more the setback. It also depends somewhat on powder burn rate, wad column construction and, naturally, pellet hardness. The harder the pellet, the less the setback. Also, the larger the pellet size, the less the setback or other distortion.

There! Confused yet? Yup, me too.

Best regards,
Bruce Buck
Shotgun Report’s Technoid

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