However my question is, could it be that the BC of my bullet at long ranges is different from the one that AB CDM provides? Do I need to adjust/true up my BC at 1500 Yard+ to get correct answers? If yes, why is my BC at 1000 yards correct but incorrect at 1500+ yards? (assuming this is not due to shot to shot MV changes).
I am also interested in learning from experienced Ko1M shooters on the process they follow to true up or tune their guns to shoot targets between 1200-3000 yards. Are there some best practices that they can share? Super grateful for your time and attention !
You can't assume the BC is correct at 1000 yards. You may have set up a broken clock. That is, your solver is only correct at 2 distances. 100 yards and whatever distance you trued it at. It results from using velocity or BC to cover up other errors. Most of the time a clock that runs a little slow or a little fast is what we wind up with. The problem is the effect of each variable changes with distance in different ways and we can never know the value of any of them with enough precision.
It's not all doom and gloom. Like wind calls, you don't have to outrun the bear. You just have to figure out how to get 1 more hit or get that hit sooner than the second place shooter. It's possible to play the game a lot better than most.
Putting the solver in the Kestral is a great idea for hunters or PRS shooters. It's less than ideal for new ELR shooters. It's more difficult to run what if cases with. Another huge issue is the conditions on your shooting mat may not be what you want to use for the calculation. Wind and temperature are the primary problems.
The android tablet version of AB has a truing function you can use, but like the rest of the solver GIGO.
A skills building truing method starts with printing out an image of your reticle on a sheet of paper. You'll need several. The ideal situation is to start at 1000 yards or just beyond and then as far past that as you can reliably spot. At least a mile, maybe just past 2k yards. With each shot, mark its location on the reticle image with the velocity for that shot. Also record the turret setting and range on the sheet. Use the solver to estimate a vertical correction for velocity. Correct each shot to the average velocity and remark the sheet. Draw a 1 moa circle around each corrected shot. Add the difference between the center of that mess and the reticle center to the turret setting to produce the desired firing solution.
Repeat that process at the longer distance using the average velocity from the first string as the correction basis.
The game is to correct velocity at the shorter distance and BC at the longer in a loop until both distances are as close to the answers you're after as they're going to get. Don't expect both to end perfectly or even within 1 click of the observed groups. You simply do not have all the information to the required accuracy to do that.
Some common error sources include:
Double dipping with the altitude/pressure measurement
Putting the Kestral on your shooting mat and ignoring what that does to temperature.
Range. While you're doing what ifs, calculate how far the range estimate needs to be off to produce a miss. That's the danger space and by a mile it's remarkably short. If you're using a number somebody told you, Google Earth, or GPS, it's fine for walking shots in but you shouldn't blame the solver when it won't true up.
Velocity. The cosine error for 6 degrees, 1 minute on a clock face, is over 15 fps for a 3000 fps bullet. If you need more than 15 fps up to true your solution, put some more effort into aligning the LabRadar with the bore. If you need to true the velocity downward, something else is likely wrong.
Accurately spotting the vertical location of an impact on flat terrain is much tougher than on a backstop. The tendency is to underestimate how low the impact was. Shots off the side that look like 3:00 or 9:00 are hitting a couple hundred yards past the target and the elevation is definitely not good at the target. Shots over the top with good windage are gone.
If you take the 5 longest bullets with the squarest meplats and combine them with the 5 shortest with the ugliest meplats, the spread in BC for the string of 10 could be 8% or more. Sorting and culling can cut it to half or a third of that. Halfway through the barrel's life, it'll start adding to that number. Seeing that aging effect is one of the reasons for the elaborate truing procedure. The idea is to build a sense of scale and you'll be able to do a coarse version of those calculations in your head. ELR barrels, and your 33XC is solidly in that category, are not done when the 100 yard groups open up. They're done when they're contributing too much to the BC spread. I chamber my own barrels and am probably a little quick to put the old ones down, but I replace them at maybe 2/3 to 3/4 of the round count that produces larger 100 groups. Shot to shot differences in BC are inconsequential at 100 yards, so looking for it there is a waste of barrel life and components. If you don't shoot past a mile very often or compete at a high level, the barrel will be useful longer. There is a strong tendency to hang on to the first barrel far too long.
