Best Shot Size for Trap – Understanding Shotgun Shells and Their Specifications

Contributed by Ted Kozloff, Brays Island Property Owner

best-shot-size-for-trap-understanding-shotgun-shells

Shell Length

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All 12 gauge shells for shooting competition trap fit a 2 ¾ inch chamber. That doesn’t mean you have to use 2 ¾ inch shells, but if you don’t you are going to feel a little lonesome. But nothing is simple. If you measure a trap shell you will find that it is a little less than 2 1/2 inches long. That’s because shells are measured uncrimped – i.e. before the shell is loaded with powder, wad and lead. The 2 ¾ inch measurement actually refers to the length of your gun’s chamber, which has to be 2 ¾ inches long to allow the crimp to unfold.

“Well,” you say, “I want to use my duck gun to shoot trap, and it has a 3 inch chamber. Can’t I use 2 ¾ in. trap shells in my gun?” The answer is yes, although some people feel that using a shell that is shorter than the chamber can adversely affect the pattern.  (A long time ago, I used a Remington 1100 with a 3 inch chamber to shoot trap, but I was such a lousy shot it was impossible to tell whether the chamber size contributed to any of the misses.)

I should emphasize that the reverse is not true – you can’t use a 3 inch shell in a 2 ¾ inch gun.  A 2 ¾ chamber won’t allow a 3 inch shell to unfold its crimp correctly. You risk blowing up the gun. Very bad idea.

So how do you know what size your gun’s chamber is? Easy – all modern guns have the chamber size engraved on the barrel near the breach, or they say something like “Use 2 3/4 inch shells”.

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Gun Powder

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You frequently see the 2 ¾ number on a box of shells twice. That is not just an empty repetition. The second reference is to the amount of propellant in the shell. In this case, the 2 ¾ number is usually followed by these letters: “Dr. Eq.” That refers to “Dram Equivalent”, and is supposed to relate to the equivalent amount of black powder (measured in drams) which will give the same muzzle velocity to the shot in the shell as the more modern powder used in the shell.

This is really archaic, and now many shell manufacturers also state the power of the propellant in terms of muzzle velocity – the velocity of the shot as it leaves the muzzle. In fact, sometimes the box states only the muzzle velocity, and not the “Dr. Eq.”

The problem with the muzzle velocity statistic is that different shell manufacturers seem to have a different idea of what muzzle velocity a certain Dr. Eq. will generate. I have three different shells in my ammo supply that all say they are 3 Dr. Eq. The problem is that each one has different muzzle velocity, ranging from 1200 to 1250 ft. per second. Go figure.

As to the amount of propellant you want in your trap shells, here’s what I do:

  • 16 yards – 2 ¾ Dr. Eq. or a muzzle velocity around 1140 fpm
  • 24 yards – 3 Dr. Eq. or a muzzle velocity around 1200 fpm
  • 24 yards and windy – 3 1/8 Dr. Eq. or muzzle velocity around 1240 fpm
  • Doubles – First shot 1 oz. lead, 2 ¾ Dr. Eq., second shot same as handicap

(I use only size 7 ½ shot. More on that in a minute.)

12 gauge shotgun shell closeup

Shell loads are truly a case of personal preference. The suggestions set out above are common, but by no means universal. You will find a lot of different opinions as to how your trap shell should be loaded. I suggest you start with my preference, then try different shells and see whether you like something else better.

On the subject of gun powder quality…… What follows is just my own personal observation, and it relates only to factory loads. It seems to me that the powder in the less expensive shells is dirtier than the powder in the more expensive shells. I reached this conclusion after examining my receiver (and sometimes the barrel) following shooting cheaper shells.

I find more black residue (probably unburned carbon) when I shoot cheaper shells. It also seems to me that cheaper shells kick more. I think that is due to the fact that the powder burns more rapidly, and possibly unevenly. Your mileage may vary.

Amount of Shot

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The weight of the shot in the shell can vary significantly and still be legal for trapshooting. Amateur Trapshooting Association (ATA) and Pacific International Trapshooting Association (PITA) rules specify that you cannot shoot more than 1 1/8 oz. of shot in a single shell. But you can shoot less if you want, and a lot of people do, using loads as small a 7/8ths of an ounce. (I use 1 1/8 oz. for all my shells, except for the first shot in doubles, where I use 1 ounce loads.) Note that as the amount of shot goes down, the muzzle velocity goes up, assuming the same amount of powder is used.

hunter loading shotgun

Size of Shot

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There are some real differences of opinion regarding size of shot – should you use 7 ½ or 8? I have even seen some people use 9’s. (Naturally, unlike shoes, size 8 is a little smaller than size 7 ½ – why should it be simple?) The proponents of 8’s argue that more shot means a better chance of hitting the target; the supporters of 7 ½’s say that you need a bigger pellet to break the target; the smaller ones may not do the job.

I’m going to take sides on this one – I think that the people who shoot size 8 shot in trap are just plain wrong. Here’s why:

  • Assuming you are shooting 1 1/8 oz. shells, then regardless of the size of the shot, the total weight of the lead in the shell is fixed.
  • If your choke does its job, the distribution of the shot inside a 30-inch circle should be pretty uniform. That means that the amount of lead per square inch in the pattern is going to be the same, regardless of which size shot you use.
  • Thus, if you place the target inside the 30 inch circle, it is going to be hit by the same amount of lead, regardless of which size shot you use.

However:

  • Smaller shot has a greater ratio of surface area to weight. (This is easy to understand – take a cannon ball that is 6 inches in diameter. It will have a surface area equal to about 113 square inches. Now cut the ball in half.  You have added 28 inches of surface area with no increase in volume or weight – thus smaller shot size means more surface area per volume)
  • More surface area means more area to “rub” on the air as the pellet flies, so a smaller pellet slows down more quickly than a larger, heavier pellet because of friction with the air.

All of which means that when size 8 shot gets to the target, it is not going as fast, and therefore doesn’t hit the target as hard, as size 7 ½ shot.

Did you ever wonder how the shot sizes are derived or why size 8 shot is smaller than size 7 1/2? The answer is quite simple. Think of  .17 inches. Then subtract the shot size from .17 to get the diameter of the shot. So size 2 shot is .15 inches in diameter; size 7 ½ shot is .095 inches in diameter.  

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Quality of Lead

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Not all lead is created equal.  The more antimony that is mixed into the lead when it is refined, the harder the resulting shot will be. Hardness translates into resistance to deformation, and resistance to deformation means that the sudden shock to the lead when the powder ignites creates fewer oval shaped pellets. The problem with an oval shaped pellet is that it doesn’t fly straight  – the odd shape causes it to veer to one side, resulting in a pattern that may have holes in it.

But antimony is expensive  –  it costs 2 to 8 times as much as lead, and the cheaper shells use less of it. (Antimony levels can go up to 6 %, but anything over ½ of 1 percent can legally be labeled “hard shot”. Don’t be fooled – find out what the actual percentage is.)

Another source of misses attributable to the quality of the lead relates to the uniformity of the pellets. Cheaper shells have more variation in the size of their shot. It is easy to see that this will affect the uniformity of the pattern as well as the length of the pattern –  the smaller pellets take longer to get there. (This is one of the major drawbacks to using reclaimed shot –  no effort is made to size the shot, so your lead can be a wide variety of sizes, which results in non-uniformity in the pattern.)

The information presented here is just the tip of the iceberg when it comes to discussion of shotgun shells. For example, did you know that the method for making shot in sizes suitable for trapshooting changed radically in the 1960’s? I didn’t.

Intrigued (or just confused)? Just talk to me on the trap range or check out my trap shooting tips.