Altitude and Patterns


My question, which I don’t think you have addressed before (if that is possible), is the effect of altitude on choke and shot size selection.

I currently shoot sporting clays at a club where the course ranges in altitude between 2,500 and 3,000 ft. When I first moved here from the flatlands, I noticed that I seemed to be breaking birds with less choke and smaller shot size than my previous experience. I realize this is purely anecdotal. I don’t know for sure even how far the targets are, how may pellets were hitting the targets, let alone how much energy they were carrying.

Last year one of our members, who likes to pattern his shotguns, posted some limited data that the same shotgun with the same chokes and shells patterned at least one choke size tighter at our club than they did in Florida.

What does the science tell us about this?

Dear Stephen,

In school I slept through most of science class. They weren’t getting into shooting anyway. But I have learned a lot about how altitude affects patterns by listening to shooters who know a heck of a lot more than I do.

Shotgun pellets are affected by the density of the air they are shot through. Sounds pretty simple. The denser the air, the more the shotgun pattern opens up. Air at high altitude is less dense than air at sea level so patterns shot at high altitude will be tighter. This was certainly the case during the 1968 Olympics held in Mexico City, which has an altitude of over 7,500 feet. Shooters were told to open their chokes to compensate for the altitude. Many people have found that a choke which produces a modified pattern at sea level will shoot a full pattern at a significant altitude.

Other things affect air density which will affect the shotgun’s pattern too. In warm weather the pattern will be tighter than in cold because cold air is denser than warm. It’s the same with dry air being denser than humid air (though this seems illogical, that’s what Mr. Science mumbles to me).

So a hot, humid day at altitude will give you the tightest pattern, while a cold dry day at the seashore will give you your most open pattern due to the denser air. Thinner air means tighter patterns.

Now, instead of just worrying about chokes and shells affecting your pattern, you have to worry about the weather and altitude. Who said shooting was easy?

Best regards,
Bruce Buck
Shotgun Report’s Technoid

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