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Old 11th September 2011, 09:36 PM
greyskullnz greyskullnz is offline
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Join Date: Aug 2009
Location: Wanganui NZ
Posts: 268

Originally Posted by Gibbs View Post
Surely, there is a simple (if a little long winded) solution to shooting in "thinner" air.
Thinner air will simply make your trajectory flatter. So to reform the original curve and restore your original zero, you have two adjusters to tweak.
1# The turret
2# The power of the gun

If you turn down the gun and dial in your original zero until the top of your trajectory is back where it was and the 55 yarder comes in back where it was, then surely all your original settings will be spot on?


The pellet speed does not vary out of the muzzle, but the terminal pellet speed at target does due to change in the coefficient of drag. Its the difference between the two speeds that counts. Changing the power setting on the air rifle isn't practical in or just before a match and will only make the effect worse and a loopier trajectory.

If you have room on the turret for multiple settings fine. If you have an adjustable turret fine. You are still going to have to dial in negative clicks at some ranges for a rise in pellet path (with two zeros now), and dial in extra come-ups (with no zero) for more dense air compared to your original set up density conditions.

It actually is temp related (when it is seen at a static location). As the temperature rises, the air gets less dense. At sea level or near sea level the magnitude shift is less. So in effect those who blame it on temp are correct, but its not the air rifle itself, or the scope changing due to temp rise/fall. Its the air itself effecting more or less drag on the pellet as the temperature rises or falls either side of what you set the rifle/pellet/trajectory settings at (at one static location over a day/week/month). Go to a different location at a different altitude and you basically have to start from scratch all over again, unless you have custom charts for your come-ups, devised for different Density Altitudes.

It is simple to do, just a bit of work in preparation, and doing it for your own rifle and original location where you set up. Then you can take it anywhere with confidence and adapt to the changing conditions. Everyone experiences the effect differently when they arrive at a course like Italy, mainly because they have come from different locations/atmospheric conditions that they have set up in. The South Africans from the high veldt would have seen a drop rather than a rise, but then they have always seen that at worlds matches, and have had to learn to adapt quickly.

Chairgun will not allow any way to show you this is happening. It always assumes you have rezero'd the rifle, and that the rifle is always on zero, even if you change the "environmental conditions". This is never the reality of the situation. You can use it as a very powerful calculator and then write it out longhand in a table of DA adjustments or use excel spreadsheet......but what you are looking for is to match the actual pellet speed difference between muzzle and target. One has to actually experience the conditions and record the data before one can formulate the ballistic solutions. Sierra Pro ballistic software will do it without assuming you are always on zero, but the drag function used is for firearms bullets and not suitable for air rifles, or 1 yard increments only up to 55 yards.

CG needs an upgrade to include this ability to solve the rise and fall due to DA, and allow a trajectory to be shown and logged without assuming a constant zero distance as that is its biggest failing. Goes to show mathematicians and software builders are not always the most intuitive shooters (and vice versa).

Getting the shift issue sorted will not give anyone an "edge", it will bring the Worlds scores in the middle range up, and closer together at the top end. Then FT returns to being a match based upon shooting skills and technique rather than chasing expensive equipment.

Last edited by greyskullnz; 11th September 2011 at 10:19 PM.
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