…. because posting about pellet guns is not remotely as depressing as posting about politics…
So…. some thoughts on accuracy.
I am probably crazy when it comes to accuracy. My expectations are probably totally out of whack with reality. Especially when you consider all the variables that go into shooting a pellet 30 yards or more downfield.
How accurate is “good enough?” Well, for most purposes “good enough” accuracy is defined as “1 inch groups”. That’s because the “kill spot” on most small game animals is about the size of a 1″ diameter circle. Even larger game sometimes have small kill spots too, and obviously more accurate is always better than less accurate. “Aim small, miss small” is a maxim in shooting that has been true since people first started launching sticks into the air with atlatls.
Some people aren’t happy with 1″ groups though. Particularly at close distances like ten meters (which is an Olympic sport, btw… the US has a 10m pellet gun team competing in London this month). Serious shooters expect to have groups well below 1/4″ at ten meters.
Obviously that’s not much room for error, considering the following:
1. Pellets are rarely uniform. Even the best commercially available pellets are produced through the use of multiple pellet molds, and as such, even if each batch was molded and de-molded perfectly, there would be differences in weight and size just due to the differences in the different molds. Add in the tendency for cast metal to have flashing, bubbles and other defects and it’s amazing that there is any consistency at all. It is not uncommon for the weights of commercial grade pellets to vary by as much as 10%, and the same is true for size.
2. Air pressure is rarely consistent. This is actually a big problem. PCP guns tend to operate at 2,000 – 3,000 psi air pressure. Air reservoirs are not highly sophisticated devices. In fact they are generally nothing but a bottle with a valve on top. The valve is held closed by a spring. When you want to put air into the bottle, you push down on the valve to open the airway and then force air into the bottle until it’s full and then you allow the valve to close. To get air out of the bottle you do the same thing. (Some bottles actually have an input and an output valve, but those are more expensive bottles). So the way this works is that you “tap” the valve to open it for a split second, which allows a burst of air to come out before the spring slams the valve shut again. The way most guns do this is with a “hammer” which slams against the valve. The hammer is cocked by compressing a spring and when you pull the trigger the spring is released, the hammer flies down a tube and smacks the valve, the air is released and flows into the breech where it then propels the pellet down the barrel. How much air is released, and how fast, is determined by the speed and weight of the hammer, the distance the valve has to travel, the air pressure inside the tank and the size of the airway in the valve. Each time you hit the tank the air pressure is reduced. Most guns get about 15 to 20 shots before the air pressure in the tank is reduced to the point that accuracy suffers and you have to “top it off” again. One reason I got the AirForce gun is that they use a massive air reservoir which allows for many more shots in the “sweet spot” before you have to pump more air into the tank.
3. All of the things that normal guns have to deal with come into play as well. How is the scope mounted? Is the barrel straight? (No barrel is actually straight, in fact determining the direction of barrel bend is part of the job of gun builders.) The trick is to have the barrel’s bend be in line with the scope or barrel sights. Gun barrels are graded the same way fishing rods are, their natural “bend” is marked and the barrel is mounted on the gun with the natural bend set so that the projectile won’t “drift” when fired. Other things that come into play are torque, vibration, flexture, etc…
So… considering all of this, how the heck can you shoot accurately?
Well, all of the things in #3 are well known and have solutions that have been in place for firearms for hundreds of years now. So that leaves items #1 and #2.
For #1 serious shooters grade and separate their pellets by weight and size. Yes, they do. Seriously. They use digital scales to weigh each pellet and they use different techniques to separate according to size. Then they put the graded pellets in tins with the weight and size marked on them. Plus they clean the pellets, removing all flash, discarding all malformed or incomplete pellets and they even wash them and in some cases lubricate them. (Some shooters believe lubricated pellets gain up to 10% more velocity than un-lubricated pellets).
For #2 the only real solution is what is called a “regulator.” Yes, that’s the same thing that scuba tanks use, and it serves the same purpose. A regulator changes the outgoing pressure of a tank from whatever the internal pressure is to a consistent pressure. Usually the regulators in use are set to 2,600 psi or something like that. A good regulator will allow the gun to have nearly identical air pressure and air volume shot after shot until the internal pressure drops below what the regulator is set at.
Regulators ain’t cheap. A decent one can cost well over $200. But serious shooters use them. Most shooters who use regulators also use 4,500 psi tanks, which are usually carbon-fiber and very costly, but they provide a lot more shots.
Really, REALLY serious shooters use what is called a “tethered” system. Instead of using a portable air reservoir bottle, they have a huge scuba tank and a regulator and run a long tube from the scuba tank to the gun. This allows thousands of shots at the same pressure before the scuba tank needs to be refilled.
So… am I gonna grade my pellets? Am I gonna buy a regulator?
Dunno. Let me see how the gun works first. But if I ever get really serious about this… mebbe so.