This is from Hornady's calculator. I have another well repspected Ballistics program on my iMac upstairs but its not worth the trouble
If your shooting experience is different that the programs so then consider.
What is the actual zero range? If the 200 yard drop is remarkably different than that shown here then the zero range is probably not the same.
What is the altitude?
What is the actual velocity?
Was there a head or tail wind? This is usually minor at RB ranges.
Cross winds can effect the projectile in both the horizontal and the vertical. But again its not significant at the ranges we usually shoot game with the RB though it may well show up if trying to shoot a match on paper in a cross wind where being out an inch is a serious detriment to a good score.
Unless the shot is chronographed as the same velocity it will be unlikely to agree with some set velocity put into the program. My 54 does not make 1900 exactly and I have not bothered to check it for several years now, 6 maybe.
That tables primary reason for being was to demonstrate that zeroing a hunting rifle at 100 is a mistake. A hunting rifle is not a target rifle from the stand point of ideal trajectory. Unless all shots are over known ranges or at close range.
For example if the 1900 fps load is zeroed at 100 we get 7.8 inches of drop from LOS at 150. If for some reason our velocity is not exactly 1900? If its 1860 then the drop will be even more. If shooting at smaller deer like some of the smaller whitetails this can result in a leg shot off with a center hold. Making the zero at 120 will reduce this to 5" +-. So if the range is misjudged by 10% its less critical.
None of these are a be all-end all. There are many things that can produce changes. This is why while these programs can be useful one must shoot his rifle at various ranges with a clean bore as it would be in a hunting situation. Find out where the ball actually falls. Where they are really valuable, to the RB shooters is in giving the shooter an idea of where he should zero his rifle for hunting.
In modern rifles where shooting at targets may run to a mile or more (a mile is the new 1000 yards some say) nowadays having something to give a ball park windage and elevation setting is nice. This will not replace shooting and using a range book to record actual results at a given range and weather conditions. But this is far from the round ball shooters needs but its a partial explanation of how "Shooter" and other similar products came into being.
Dan