Shot Talk

Think how many times you’ve heard one of these bits of lore passed off as conventional wisdom: “When it’s cold, you need a different hunting load to compensate for the birds’ thicker fat and heavier muscles, which make them harder to kill.” Or “Late-season birds are tougher to bring down because of their thicker feathers and heavier layers of down.” Let’s examine the facts.
    The following is undeniable for wild birds. As fall wears on into winter—which means from about November 1 to the end of bird season in northern latitudes—waterfowl and upland birds have less access to food. This is due principally to snow cover. So fat layers and muscles of wild gamebirds do not get thicker or heavier as fall hunting seasons progress. If anything, these tissues become more depleted as wild birds’ overall body weights decrease due to lack of food.
    As far as birds being “more feathered out” late in the season, that’s another fallacy. By November 1 they have all of the head, neck, body and flight feathers that they’re going to get. So by December 15 they don’t have any more feathers than they do November 1. They may have slightly more insulating down. But in my necropsies of thousands of waterfowl and pheasants, down has never proven to be a significant inhibitor to pellet penetration, regardless of thickness. So, no, there is nothing significantly different physically about wild gamebirds in late fall and winter versus, say, October that makes them harder to kill.
    What is changing as the season wears on is the ambient temperature. As winter deepens, average daily temperatures decline. Many hunts in December and January in northern-tier states take place in sub-freezing temperatures. In addition, with wild birds, as the season wears on, the survivors become increasingly wary. The later in the season it gets, the farther away upland birds tend to flush and the poorer waterfowl tend to decoy. The result is that the average distances of shots taken by late-season hunters are significantly longer than the average distances of shots taken earlier in the season. And as distances increase, the ballistic effects on the performance of shotshell loads are exponential decreases in pattern densities and per-pellet retained energies.
    All shotshells—factory or reloaded—shed velocity and pattern density quicker as the temperature drops and the atmosphere becomes denser. The denser the atmosphere, the more air resistance confronts the projectiles. The denser the medium that a projectile has to pass through, the more quickly it slows down. If the projectile is deformed (as happens to the vast majority of lead pellets and most soft nontoxic pellets), it will diverge from the point of aim at an ever-greater angle the denser the atmosphere becomes. Both of these negative exterior ballistic effects increase as distance increases, and they show up as ever-declining velocities and patterns.
    This explains why shotgunners who take the time to pattern test are sometimes miffed when they see that their pet load that produced pattern-quality “X” during the summer suddenly starts producing lower pattern values during the fall and winter. If you take the time to set up downrange-velocity-measuring devices, the velocity measured for a given load during the summer is almost always higher than that measured for the same load from the same gun and choke during the winter.
    It is true that as temperatures drop, primers and propellants do not generate as much energy in the closed space of a shotshell load. This also contributes to lower instrumental velocities for any given load in cold temperatures compared to warm temperatures. How much of a drop in velocity occurs from warm weather to cold? The answer depends on the load.  Generally, those loads featuring slow-burning propellants and low chamber pressures suffer more velocity loss from the effects of declining temperature than do loads with faster-burning propellants and higher chamber pressures. All heavy-shot-charge loads—lead and nontoxic—tend to contain slow-burning propellants, so they’re especially vulnerable. It is not unusual to see such loads losing as much as 50 fps in instrumental velocity as the temperature declines from 70° F to 20° F. Loads with less-sensitive propellants might lose only 20 fps over the same temperature drop.
    How much of a change occurs in patterns from warm weather to cold? This is a function of choke. As a general rule of thumb, I have always found patterns from an Improved Cylinder choke open up more from the effects of cold weather than those from a Full choke. This change can open patterns as much as 15 percent for some lead loads when fired through a Skeet or Improved Cylinder choke at distances of 40 yards, and 20 percent or more when fired through the same choke at distances of 50 yards. From my testing, these same loads fired through a Full choke will generally lose more like 8 to 10 percent at 40 yards and about 15 percent at 50 yards. These declines in pattern density occur as outdoor temperatures drop below 40° F, and especially below 20° F.
    Now the important question becomes: Are these declines in downrange velocity and pattern quality important? For a hunter, any decline in pattern quality is much more important to the performance of the load than is a small decline in velocity. Long-range shotgunners, particularly those who pass-shoot at distances of 50 to 70 yards (common for goose hunters), are lucky to develop marginally lethal patterns at 60 yards through their pet guns and best chokes with their pet loads at 70° F. When the temperature falls to 20° F, these same shells through these same gun/choke combinations often become sub-lethal in pattern quality. This can greatly contribute to wounding losses—and the perception that the birds have become harder to kill. Unfortunately, hunters who are developing marginal killing patterns at extreme range during early season temperatures really have no choke options to improve pattern density as the season wears on and ambient temperatures drop. Why? They’re probably already using their “best” chokes. Another negative of increasing atmospheric density is that shotshell pellets retain less energy over all distances. This is a poorly appreciated aspect of shotgunning, but it is a very real problem. 
    Many waterfowlers and upland hunters switch to larger pellets later in the season as they find their early season choices becoming increasingly ineffective. Often they switch to pellets one size larger to get the same per-pellet energy during cold weather. For example, as a gross rule of thumb, a No. 4 lead pellet at 20° F behaves about like a No. 5 pellet at 60° F. The same can be said for a No. 1 steel pellet versus a No. 2 steel pellet—and so on. So it is indeed a good move during the late fall and winter to go up one pellet size to compensate for the energy-eroding effects of a denser atmosphere. But if you can’t get a similar pattern density with the larger pellets, then a decrease of about 10 yards in maximum shooting distance also becomes necessary.
    So the culprit in late-season shooting is not that the birds are harder to kill; it’s that ammunition performs less effectively and shots are typically farther away. The solution is to go to one-size-larger pellets and to be willing to decrease maximum shooting distances.

To correspond with Tom Roster or to order his reloading manual on buffered lead and bismuth shotshells, his HEVI-Shot reloading manual, his updated 75-page Shotgun Barrel Modification Manual or his instructional shooting DVDs, contact Tom Roster, 1190 Lynnewood Blvd., Klamath Falls, OR 97601; 541-884-2974; tomroster@charter.net.