The math IS NOT the math with ballistic calculators, unfortunately. As with anything, anything worth doing well involves particular nuances that factor in the separating bad, good and excellent.
There is some theory built into of the math calculators. More on that later, but these theories even though well founded, due to various micro inputs from imperfect beings, some of the math is averaged. The world and technology is not perfect. Point being, imperfection is introduced the entire time.
Here's a good example on how recoil management alone can vary inputs if data:
Other examples can be things that effect the rifles harmonics, including head position and head pressure. Even parallax. In short, what I consider to be fundamentals. Despite how small, as errors compound, they become more apparent.
Easy enough right?
When we get into things like spin drift, and at distances that spin drift actually matters, most calculators are incorrect. They use things like miller stability, however, when measured, it's close but not THAT close. If doc from AB is still on here maybe he can talk more about the math, as it was either him or Litz that I learned that a flat rate value was given that often over compensates on SD.
The further out you go, those errors compound, as mentioned before. From what I've seen and been apart of, I can confidently tell you that monos, since they are longer, and thus require different twist rates, will have a different spin drift value, then a lead core bullet in the same caliber and weight category. The math is closer to 1% of drop for monos or hyper twist barrels and 2.5% of drop for lead core projectiles using standard twist barrels.
So there is another example.
BC is another concept, often misused or misunderstood as it relates to data. I won't get into unless asked, as I'm actually getting bored typing on a phone.