Nuclear Worker:
Your math and Apps seem way off … in a fairly large way.
You did not post it, but I suspect your 6BR has an MV somewhere around 2,900 fps (depending on bullet, bullet weight, barrel length, charge, powder etc …..).
If so, and you are using a high end well designed high BC bullet, you should be seeing 600 yard come-ups around 11 MOA or so (based on a 100 yard zero).
I'd be happy to help …. But I suspect you're missing some critical data and/or have put it in the apps wrong. If you want and are able, Drop me a private PM sending me your email … and following that I'd want you to send me a snapshot of your data entry page for ISTRELOK along with all your rifle/bullet info (I suspect you are using hand-loads).Hopefully we will be able to fix it there.
I use both apps (Stelok more) and both are normally spot on. I suspect you either have your BC input incorrectly, MV off, or ….
Happy to help…. Drop me a line.
I shoot 6mm all the time out to 1,000 yards at matches and hold a national record so am pretty aware of what this cartridge can do, and what it's ballistics are doing …. And routinely use the APPS you are having issues with. Drop me a line…. Happy to help.