One of the things which often gets mentioned is that pellet wobble will affect the BC of a pellet, leading to large differences in measured BCs. I have never been comfortable with this simple and logical conclusion, the reason being that, while pellet wobble will affect BC values, it also affects a whole lot of other things in the pellet flight which should make it obvious. I have never seen anyone mention seeing anything about strange about their pellet’s behaviour when low BCs have been measured.
Since firing pellets with a known yaw angle to get consistent wobble is rather difficult, I used the usual easy way out of the problem by modelling the effects. The trajectory program is the usual one I use on pellets with the same data from the 15.9 grain .22 AA Field pellet. The modelling was simple with trajectories calculated for pellet yaw angles from zero up to ten degrees in two degree steps, with a muzzle velocity of 850 ft/sec. I took readings for the velocity at 30 and 50 yards along with the calculated error in the pellet position at the same ranges. I then used Chairgun for each range to calculate the average BC based on the calculated velocity.
The first figure shows the calculated velocity drop in ft/sec over 30 and 50 yards for each yaw angle.
The figure below shows how the calculated BC varies with yaw angle for both the 30 and 50 yard ranges.
So there is a demonstrable effect on the value of BC from pellet yaw angle. In this case, the value fell from .029 with no yaw down to .023 with ten degrees of yaw. So far so good.
Below is a graph of the pellet impact point error in inches at 30 and 50 yards range for the different yaw angles.
Group size can be expected to be twice the error value, as the error can be in any direction. Now, I think that most shooters would notice a group size of 34 inches at 50 yards range. Even a four-inch group size would be considered completely unacceptable, but you can get that with just over one degree of yaw at 50 yards, two degrees of yaw at 30 yards. Yaw angles of one or two degrees made no difference to the calculated BC value. For those who don’t like graphs, the table below sums the results.
So the problem I have is that you cannot have a yaw angle large enough to cause a measurable change in BC without having a large error at the target, in many cases too large for the pellet to be in any way usable. All the work I have done in the past suggests that pellet angles have to be below one degree for an acceptable group size. My feeling is that the reason for BC variations is far more complex than some pellets having more yaw (wobble) than others.
The modelling may have errors in it, however the most important variables have been derived from experimental results. The fact is that even if the modelling is 50% in error, it still seems unlikely that pellet wobble which is sufficient to cause significant differences in BC will not produce large errors and groups at the targets.
Since firing pellets with a known yaw angle to get consistent wobble is rather difficult, I used the usual easy way out of the problem by modelling the effects. The trajectory program is the usual one I use on pellets with the same data from the 15.9 grain .22 AA Field pellet. The modelling was simple with trajectories calculated for pellet yaw angles from zero up to ten degrees in two degree steps, with a muzzle velocity of 850 ft/sec. I took readings for the velocity at 30 and 50 yards along with the calculated error in the pellet position at the same ranges. I then used Chairgun for each range to calculate the average BC based on the calculated velocity.
The first figure shows the calculated velocity drop in ft/sec over 30 and 50 yards for each yaw angle.
The figure below shows how the calculated BC varies with yaw angle for both the 30 and 50 yard ranges.
So there is a demonstrable effect on the value of BC from pellet yaw angle. In this case, the value fell from .029 with no yaw down to .023 with ten degrees of yaw. So far so good.
Below is a graph of the pellet impact point error in inches at 30 and 50 yards range for the different yaw angles.
Group size can be expected to be twice the error value, as the error can be in any direction. Now, I think that most shooters would notice a group size of 34 inches at 50 yards range. Even a four-inch group size would be considered completely unacceptable, but you can get that with just over one degree of yaw at 50 yards, two degrees of yaw at 30 yards. Yaw angles of one or two degrees made no difference to the calculated BC value. For those who don’t like graphs, the table below sums the results.
So the problem I have is that you cannot have a yaw angle large enough to cause a measurable change in BC without having a large error at the target, in many cases too large for the pellet to be in any way usable. All the work I have done in the past suggests that pellet angles have to be below one degree for an acceptable group size. My feeling is that the reason for BC variations is far more complex than some pellets having more yaw (wobble) than others.
The modelling may have errors in it, however the most important variables have been derived from experimental results. The fact is that even if the modelling is 50% in error, it still seems unlikely that pellet wobble which is sufficient to cause significant differences in BC will not produce large errors and groups at the targets.
