Chronographs
Chronographs are a very useful tool that the airgunner can use for research and for honing one's ability to replicate a good shot. Let me explain:
PCP airguns use a reservoir of pressure for their power source. And if you are shooting an unregulated PCP, then your gun will have what is called a "sweet spot" in the bell curve of the fill pressure. For instance, I have a PCP gun that fills to 3000 psi. The first 5 or 6 shots of the fill are slower because the pressure in the tube is slightly greater than what the ideal pressure is for the valve to close the same speed each time, thus allowing the same amount of air through for each shot. As the fill pressure nears the "sweet spot", the velocity goes up and is constant for a series of shots. And eventually, the velocity begins to slow down as the pressure is less than is optimum for repeatable performance from the valve.
How do I know this? I tested the gun over a chronograph. It shows me where in the shot count I should be able to expect repeatable performance for a known pellet weight, for a known number of shots. This is especially crucial to the competitor, and it also has a use for the hunter as well. Competitors need to know that their shots will go exactly where they want it to in order to score well. Hunters need to know the limits of their gun, how many shots they have to bag the game, and how powerful the gun is to begin with.
With a chronograph, you can measure the speed of the pellet, plug it in to a ballistic calculator and find the footpounds of energy your gun delivers. And the level of energy is different with each kind of pellet due to the different weights they are offered in by the manufacturers. Knowing that your airgun puts out 30 fpe, you can feel confident in taking that shot at a groundhog. If your airgun is putting out 6 fpe, you need to pass on the groundhog and get a more powerful airgun.
I often cringe when I hear politicians and gun control proponents claiming that an airgun shooting an 8 grain pellet approaches the power of a .45 caliber centerfire cartridge because it shoots as fast. All they looked at was the velocity. If velocity killed, then we'd all be dead because we are bombarded each day with rays of light that are going at almost inconceivable speeds. It is a combination of the weight of a projectile, coupled with the velocity, that gives it the power to harm. And there is a world of difference between an 8 grain pellet and a 200+ grain bullet!
Chronographs work by measuring the shadow of a projectile as it passes over the sensors. The best way to get a good measurement is to make sure you have an adequate light source (don't use fluorescent bulbs....the flicker they give off makes it impossible to use them with a chronograph) and that you shoot your gun from a common distance each time. This can be done inside if you have room and an adequate backstop, or outside. I've found cloudy days to be especially useful when shooting outside. The clouds diffuse the direct sunlight, and you get some very good readings. If shooting inside, you need to position lights over the sensors, and often need to place diffuser panels between the light and the sensor itself. Take a look at the chronograph selection and you will see some examples of different chronographs, the diffusers, and some light sources.
So use a chronograph for research, honing your skill, and determining the power level of your gun. But be careful....you can get addicted to your chronograph, and you will become a slave to it. I use my chronograph to check my gun's performance if I haven't shot it for some time, to remind myself of a particular pellet's performance from that particular gun, and to test new equipment. But I don't live behind one, and neither should you. So go enjoy your air gun shooting!
