Fishinwrench, I gave a lot of thought to this reply before deciding to send it. It is long in order to give a well considered response.
I hope it is received in the spirit with which it is sent.
It may serve to give a little more credence to the use of trajectory prediction programmes, of which Chairgun is an excellent example in the airgun world, and to build a little more confidence in the use of such ballistic programmes for those who might want to try them.
Back in 2004 when this popular subject was doing the rounds I carried out the following study:
November 2004 after doing all the necessary homework and data collection I applied it to a programme that Steve Woodward had designed* and Perry Babbin had resolved into his excellent graphics models.
Dave Eades' Chairgun programme is a further development to that model and uses the GA standard rather than the G1. I had a little to do with supplying Dave Eades ( Harry's Lad) with velocity and bc data I collected from shots over a chronograph from 50 out to 200 yards to determine the progessive changes in bc with range and velocity.
November 2004: After establishing all the necessary data that of course included average mv, scope axis height at the muzzle, actual scope click value and zeroing at 50 yards under the prevailing ambient pressure, altitude, temperature and humidity, the following protocol was followed:
With my target taped to a box it was first set at 100 yards ( all yardage was laser measured ). I had been doing virtually all my shooting at 100 yards or 71 yards to that point in time.
OK one shot was fired at 100 yards; walk down move the box back to 90 yards, check the range back to the 100 and then to the chair in the shed, walk back to the chair and re-check to the box ; re-set the sight clicks for 90 yds according to the table made from the ballistic program * and double side taped along the top of the scope. Shoot one shot at 90 yrds. Walk down and reset the box to 80 yrds etc etc to 70, 60 50, 40, and 30 yards.
Shooting was done with two classical leather sand filled benchrest bags and my interpretation of benchrest technique. Before triggering each shot the rifle was set to centre the cross hairs in the middle of the 1 inch square on 16 x power. The rifle was then gently "bumped" in two or three places. If the sight moved to settle more than approximately say an eigth of an inch at the target plane it was re-adjusted and tested again until satisfactory. It was then gently cradled and the shot fired.
The target bellow shows the eight shots all impacted in the one inch x one inch square that was the criterion aiming mark.
I think that is a pretty fair indication of the potential fiield use of a ballistic programme. No shot has impacted further than approx half an inch from the POA at the middle of the 1 inch square.
Chairgun is sophisticated and developed to allow ambient data inputs enabling previously necessary real time on-the-spot preliminary testing, such as you are using, to be pretty much abandoned.
The caveat is that the full set of data input is necessary to allow it to show its best. Armed with a small weather station to give me ambient conditions of temperature, pressure and humidity (in order of importance) , my own pellet to range /ballistic pellet coefficients for my rifles and the other data indicated above, and rangefinder, I can go to any location and be confident of the results out to extreme ranges. Providing wind reading skills or lack thereof don't let the side down.
The rifle used was an FX Excalibre/FX 2000/Tarantula, which has shot over 70 sub inch 100 yd groups before and after this study; and literally hundreds of rabbits to 150+ yards . Pellets were 15.9 gr JSB Exacts shot at 900 fps average. The rifle has no regulator and so has a very tight velocity consistency in its plateaued range, 170 to 150 bar.
Please expand the target for better view. ........... Kind regards, Harry.
