Speed, Distance and Time
The formula is an old one most learned in school, but it has a strong relationship to the shooting sports. Next time you prepare to shoot, take a minute to better understand the top of the shell box in regard to the feet per second (FPS) and the shot size. There is a direct correlation to the shot size and the FPS because heavier shot requires more power and thus can produce more speed. For basics, take a look at the 2.75” shot shell in a #8, 1 ounce load with 410 pellets in the shell. A 7/8 load would have slightly less pellets (359) and a #9, more pellets (585). Now a heavy load of say steel for waterfowl at a #2 shot size 1 ounce load would only have about 125 pellets. What starts to differ to push these pellets is the speed. Those #8 loads at 1200 FPS and those #2 loads at 1550 FPS differ because of the weight of the load. Along with that speed comes recoil. Finally keep in mind the speed of sound is roughly 1125 FPS, so some loads exceed the speed of sound at the muzzle.
Now back to the old formula of speed equals distance divided by time (S=D/T) and how it relates to your trap loads. Others also look at this as a way to understand lead. So, a slight difference in the formula lead equals the velocity of the target times the time of flight. It is known that a pattern of shot takes about 0.12 seconds to travel 40 yards, and we know a target moving at about 50 MPH (73 feet per second) will travel almost 8 feet in those 0.12 seconds. Math then tells us we need a eight-foot lead to break the target. I know that seems a lot, but let’s convert that to the width of a barrel as one looks at the target and estimates the lead. To do this we simply divide the lead in feet by the length of the barrel. So that eight-foot lead is now 3.7 barrels for a 26” barrel, 3.4 barrels for a 28” barrel and 3.2 barrels for s 30-inch barrel.
By substituting 32 yards (96 feet) for the distance we typically break trap and knowing from the use of a Garmin Xero S1 that most pull the trigger at about .5 seconds we get a FPS of 192 FPS. So, what gives? That is a far cry from the box top that says 1200 FPS. What one needs to understand is that “1200” FPS is at the muzzle of the gun and so many variables are reducing that speed until it hits the target. That also helps to explain why we cannot see the shot leave the barrel, but many do see it as it approaches the target. Sometimes the muzzle velocity makes for confusion as the mental picture is we can shoot directly at the moving target because we have shot moving at such a high rate of speed. But in reality, soon after it leaves the barrel the shot is slowing dramatically and might take over a second to reach the moving clay. In that same period the target moving at almost 50MPH has traveled nearly eight feet in that one second.
Wow, that’s a lot of information! What I want readers to understand is what is on the box top plays a role in how one breaks targets if you simply do the math. Of course, we don’t simply do the math we grab a box of shells and go shoot. What stands as most important is the lead has to be accomplished and perhaps how we explain what we mean by lead is supported in this article. Sit down with your youth shooter and walk them through how lead is both formulated, perceived and how lead is functionalized. A final thought is a quote I posted sometime back that goes like this, “When you miss, 80% of the time, it is because you were behind it. The other 20% of the time, it is because you were way behind it”.