The BSZ trick only works reliably when you have a bunch of people shooting the same ammo with the same sights and don't want to bother getting range time somewhere that has pits out to 300yds because it's easier to find a 25yd pistol range.
Once you change your sight height or barrel length (changing both sight radius and muzzle velocity) or ammo you are on your own.
Think about it, if your line of sight is higher, then at 25yds you'll have to have the barrel angled up higher to hit the same spot as you would with a lower line of sight. That means the bullet is going to be way higher at 300 than you expected. Also, if the bullet is going slower out of your shorter barrel, than it will come down a little sooner and hit lower at 300. The "standard" charts pick some "standard/random" sight height. Any worthwhile ballistics program will allow you to put in sight height, as the Hornady web site does. Also remember that unless you are actually measuring your muzzle velocity, then you can be waaaaay off from what it says on the box and your numbers will be off accordingly.
The real trick you want to do is to find your zeroes at 100yd, 200yd, and 300yd, pick a sight setting that keeps you more-or-less centered, and then see where you hit at 25yds. Then at least you can check your zero at 25yds if you need to. After that, if you ever need to supply a few hundred thousand people with your same rifle, ammo, and setup, you can save them a ton of time and energy setting up their rifles with your new BSZ.
-J.
