The recent thread on crossover suggested that some people are not aware of how a pellet moves in the air when fired from a rifled barrel. Everyone knows that as soon as a pellet leaves the barrel it starts to accelerate towards the ground giving a curved trajectory. However, any spinning projectile also flies in a curve to the right or the left of the barrel line of fire depending on the barrel twist rate, twist direction and on the pellet aerodynamic design. This curvature is much less pronounced on a pellet out to 50 yards but it still exists whereas you are looking in a straight line through your sights. This means that as you look through your sights the pellet will only truly be in the position you are viewing at one point which is your zero range. Figures 1 and 2 will hopefully help to explain. The horizontal numbers are the drift in inches and the vertical numbers are the range in yards. The values are for a .22 pellet but, do not take them as being exact as the value will change depending on the calibre and what design of pellet you are using. In figure 1 the red line represents the pellet trajectory relative to the barrel and the line along which the barrel is pointing (vertical axis). The blue line represents the sight line which is not looking straight down the barrel as the pellet follows a curved trajectory and your sight is angled off to intersect the pellet at the zero range. The zero range is approximately 30 yards. You can see how the pellet is offset from your sight line at all other ranges. Figure 2 shows how much the pellet is offset depending on the range. In this figure the vertical axis is your sight line. The first thing that strikes you is that the offset values in figure 2 are relatively small. Even at 50 yards you are only looking at an error less than the pellet diameter. When this is combined with all the other errors such as wind speed etc then it is a small part of the total error. If you take a more severe case for a different pellet design then the error at 50 yards is approximately doubled, but, it is still less than the error given by a 1mph cross wind on the same pellet at the same range. Now I have no wish at all to start a calibre debate, but, the curve on .177 pellets is less than it is on the identical design .22 pellets due to the lower gyroscopic stability of the smaller calibre. Hence the errors at different ranges will be less but again it all depends on the individual pellet designs since the .177 designs are seldom exactly the same as their .22 relatives. The effects are relatively small and will go un-noticed in most cases. Where you may see an effect is in extreme range shooting, but, as you presumably won’t be using a 30 yard zero for such shooting, the effect will be reduced as far as you the shooter is concerned since you will be automatically compensating with the longer zero range. You may see a change in the POI when you go from one pellet make to another, but again, it should be small unless you change from a stable to an unstable pellet design. One time you may notice something is when the wind drift on your pellet appears to be worse if the wind comes from say right to left than it is if the wind comes the left to right. This is due to the difference between the sight line and the pellet drift. Suppose the pellet is in a 1mph cross wind. The pellet trajectory will move by about half an inch at 50 yards left or right depending on the wind direction. So, if the wind is from right to left the POI will be around 0.7 inches from the sight line, but if the wind is from left to right the POI will only be 0.3 inches away from your sight line causing you to think the wind has less effect on the pellet trajectory. It doesn’t, it just appears to.