Shotgun Pattern Density Calculator (Choke, Shot Size & Range)

How it works

pellets = payload ÷ pellet mass, pellet mass = π/6 d³ ρ · pellets in 30″ @ 40 yd = count × choke % (cyl 40, IC 50, mod 60, full 70) · density scales ≈ (35 ÷ (range − 5))² · per-pellet energy from retained velocity, which falls faster for small, light pellets

A shotgun kills with a cloud of pellets, so two things must both be true at the target: enough pellets must arrive inside the vital area to guarantee several strikes, and each must carry enough energy to penetrate. The count comes from dividing the payload by the mass of one pellet, which grows with the cube of its diameter — hence small shot for dense patterns on small birds and large shot for energy on geese — and the choke sets what fraction of them stay inside a thirty-inch circle at forty yards, the industry's reference. As range grows the pattern widens and density falls roughly with the square of distance while pellet velocity decays, and whichever limit is reached first sets the effective range; steel's low density and tungsten's high density move that limit in opposite directions.

Worked example

An ounce and an eighth of lead #6 holds about 250 pellets; a modified choke puts 60% — around 150 — in a 30″ circle at 40 yd. On pheasant (90 pellets and 1.5 ft·lb needed) the pattern stays dense enough to about 50 yd, and each #6 pellet still carries roughly 2.3 ft·lb at 40 yd (about 2.0 at 45), so this is a true 40–45 yd pheasant load with density, not energy, setting the limit; steel #6 (355 lighter pellets) would be too weak beyond about 30 yd — steel #4 is the equivalent.

Frequently asked questions