I’m in Coalinga, CA for the California State Service Rifle Championships. I have no ambitions (or chance) of winning anything, but having only shot on 200 yard ranges, I wanted to try shooting at a full 600 yard range. Normally, I shoot 69 grain bullets, but for this occasion, I loaded up some 77 grain bullets. I settled on 77 grain bullets because, unlike 80 grain bullets, I can still load them to 2.260″ COAL and shoot them out of magazines (necessary for the rapid fire strings), but they have ballistic coefficients high enough to not completely suck at 600 yards. Most good High Power/Service Rifle shooters shoot 69-77gr for 200-300 yards, and 80 grains for the 600 yard line, but I decided having one cartridge would be logistically simpler. Anyway, I spent some time this past week developing loads, and my final recipe (24gr of TAC and CCI 450s in LC primers) seemed to push those bullets at around 2740fps.
To help me calculate my come-ups and wind drift for the 300 and 600 yard line, I bought two ballistic apps for my iPhone: Ballistic and iSnipe. Which did I like better? Neither. They were both wrong. I punched in the BC for my bullet (or in the case of Ballistic, selected my bullet from a list), muzzle velocity, that I had a 200yd zero, my altitude, temperature, approximate humidity (dry), and everything else I can think of. Both apps gave me the same numbers: 3 MOA up for 300yds, 15 MOA up for 600 yds. I shot a team match today, and actually got to find out what my come-ups were. They were 2 MOA and 11 MOA for 300 and 600 yards respectively.
So how did the algorithm fail? I don’t know. Maybe Nosler’s advertised BC for the bullets is incorrect. Maybe my muzzle velocity was incorrect, although assuming everything else is correct, my bullets would have had to start at 3150fps to get those come-ups. Maybe I am somehow aiming higher at the 300 and 600 yard lines than I do at 200, although seeing how the aiming blacks are the same angular size, that doesn’t sound likely either. It’s a mystery. But either way, for my particular purpose, both apps failed me. Of course, YMMV.
I use a number of Ballistic Calcylators, in cluding the free “Point Blank” application that is available free at http://www.huntingnut.com and the iPhone applications iSnipe and Ballistic. All provide very similar results, which match the ballistic tables printed in my reloading manuals and online ballistic calculators.
Are they perfect predictors? Absolutely not. The Ballistic Coefficient of a particualr bullet will vary as its velocity varies and as the degree of stabilization varies. In other words, identical bullets will have different BCs depending on the barrel they are shot out of, initial alignment of the bullet to the bores, initial velocities, etc. Further, the vBC’s will constantly change as the bullet’s velocity decreases.
Nevertheless, Ballistic Calculators can be quite useful. Before I got a chronograph I used Point Blank to estimate the velocity on my 7mm Rem Mag hunting loads. To do so I simply measuered bullet drop at 100, 200 and 300 yards, then varied the Point Blank inputs (BC, Velocith a Zero Range) until I had a calculated trajectory that matched the observed trajectory. Later, when I got a chronograph, the actual average velocity was measured to be within 10fps of the calculated velocity.
The dificulties experienced in this case demonstrate that there is simply no substitue for actual range experience. What needs to be done is to measure average velocity. Then measure trajectory at several ranges and reverse calculate the BC. It wil then be possible to get more accurate results from a Ballistic Calculator.
That said, I have been very pleased with the Ballistic Calculator results when the average velocity and manufacturer’s BC were the known starting points.
My advice to anyone considering the iSnipe and Ballistic calculators would be to get them. I prefer the iSnipe app by a slight margin.
Probably not enough to matter but have you checked how accurate your scope MOA settings are to real world.
I have a Bushnell elite 6500 2.5-16×50 Mil and for one full turn on the knob (12 MOA) real world shange is 14.3MOA both wind and elevation.
For my scope MOA indicated in Brackets
Shoot a group at 100 yards at each change. First group at an aim point( don’t change the aim point throughout), then come up one full turn (12MOA)shoot another group, then left one half turn(6MOA) then right one turn (12MOA)then down one turn(12MOA), left one turn(12MOA) the back to right one half turn(6MOA). Should have a nice box with good idea of real world moa. measure centre of groups to each other in inches and divide by 1.047 to get moa.
Good point, although I was using this in Service Rifle competition, where we shoot with iron sights. It’s still entirely possible that the sights aren’t exactly 1/4 MOA-per-click as they claim, and that could account for the discrepancy.
The interesting approach to shooting. How have acted in the championship?