What’s the ‘sweet spot’? Does it affect accuracy? Our guru knows
I shoot an Air Arms S510 PCP rifle and I’ve heard people talking about the sweet spot, but I don’t know what it means. What is it and how does it make a gun more accurate? My gun will shoot ¾” groups at 35 yards all day long, but if I could make it better, then I want to.
Hello Phil Unless your rifle has a regulator, the velocity of your pellet at the muzzle will be affected by the pressure of the air in the reservoir, and only the latest S510s have one fitted. The way most PCP rifles work is as follows: As you cock them, you compress the hammer spring so that when you press the trigger, the hammer flies forward and hits the knock- open valve in the end of the air reservoir. This opens for a tiny fraction of a second, allowing air to flow through the action and up into the barrel to drive the pellet. As quickly as it opens, the remaining pressure in the reservoir closes it again.
When the reservoir is at its maximum fill pressure, the hammer can’t open the valve to the maximum, so the gun shoots a few per cent slower. As the reservoir pressure reduces, the force of the hammer can open the valve for longer and velocity increases. Finally, as the reservoir pressure drops below the optimum amount, velocity tapers off.
Patiently shooting your rifle through a chronograph, from maximum to minimum pressures, and logging the figures will show this clearly. The sweet spot is the part of this curve where the difference between the highest and lowest velocity is so small that it makes little difference to the trajectory. I ran that test on my Air Arms S410 and found that between 180 and 150bar the velocity change was very small and I got some 45 near- perfect shots, which is more than I’ll ever need from a hunting gun.
ABOVE: Learning which fill pressure works best is an easy job
RIGHT: 45 precision shots is enough for anybody