By Phil Bourjaily

Patterning a shotgun is one of the essential chores that we all should do during the off-season. It's not fun, but neither is missing and losing birds. Testing your shotgun and load will tell you if the combination delivers enough pellets on target to make clean kills, and whether the pattern is broad enough to easily intercept flying birds. Skip patterning, and you're firing blind when you shoot at a duck or goose.

Here are seven things to keep in mind as you search for the perfect shot pattern for waterfowl.

1. No Two Patterns Are Alike

Like snowflakes and fingerprints, no two shot patterns are exactly the same. In fact, there's a surprising amount of variation from one to the next. Therefore, you need to shoot more than one pattern with each gun, choke, and load combination you are testing. Ammo manufacturers take an average of 25 shots, although there's a diminishing return after 10.

2. No Two Shotshells Are Alike

If you're interested in figuring out percentages, you need to know exactly how many pellets your shotgun shells contain. Open up five cartridges from the same box, count the pellets, and figure out the average. Pellet counts, and even sizes, can vary a great deal among different lots of the same ammunition.

3. There Is No Such Thing as an Even Pattern

The mythical "even" pattern doesn't exist. Patterns are denser in the center and sparser at the fringes of a 30-inch circle, which represents the maximum effective spread of a shot pattern. Within the bell-curve distribution of pellets in a pattern, you will find clumps and gaps. All patterns have them. Changing chokes is one way to reduce the number of gaps. At close range, many chokes are too tight, leaving gaps in the pattern fringe. At longer ranges, a tighter choke may put more pellets in the pattern, closing some gaps.

4. Altitude and Weather Affect Patterns

If you pattern your gun in Portland, Maine, near sea level, and then take a goose hunting trip to Colorado's Front Range, the thinner air at 5,000 feet will cause you to shoot slightly tighter patterns. On the other hand, dense, cold air tends to open patterns. If you hunt in single-digit temperatures, your gun will shoot a slightly more open pattern than it does when you test it on an 80-degree summer day.

5. Pattern at the Same Distance You Shoot Your Birds

Everyone wants to shoot 90 percent patterns at 40 yards, but what does that choke-load combination look like at 25 yards, where you shoot your birds? At that close range, chances are you'll see a tight clump of pellets in the center and a sparse pattern along the fringes, which provides little margin for error. If that's the case, open your choke or go to a load like Federal's Black Cloud Close Range or Winchester's Xpert, which often shoot more open patterns than other shells.

6. A Pattern Is a 2-D Picture of a 3-D Phenomenon

Shot clouds have height, width, and depth. A pattern on a piece of paper shows only the spread of the pattern, not the length of its shot string. That said, shot strings with hard, round steel pellets are fairly short. "Shot stringing," or the lengthening of the shot column, therefore becomes a factor only when you take long, 90-degree crossing shots that cause some pellets to arrive too late to hit the target. The majority of shots at waterfowl, however, are taken at closer ranges and at less extreme angles.

7. Pellets Kill, Not Percentages

Pattern analysis can be as statistical as you want, or as simple as counting holes. Generally speaking, if your choke and load combination puts 90 to 100 pellets inside a 30-inch circle, that's enough to ensure vital hits on large ducks. For geese, you want to see 55 to 65 hits, and for small ducks about 130.

Basic Patterning Materials All you need for patterning is a roll of paper at least 36 inches wide, a 4x4-foot sheet of ply-wood, and a staple gun. You can make a crude compass with 15 inches of string and a felt-tip marker for drawing 30-inch circles.