Yep, like most things in life; garbage in, garbage out.
That said, height of scope center above bore center is easily measured. Same with barrel twist, and length. Velocity can be measured with a chronograph (ask around, you shoot well enough and are responsible enough not to shoot the gear, I’ll bet some our local shooters will let you put some rounds through the screens).
Failing that, estimate your velocity from loading tables, run that through your ballistic calculator on your cell phone, then go go to the range EARLY in morning near first light and check actual elevations at the known distances (for instance, 300, 400, 500, 600). That info will be pretty dog gone good. Log it, and make a little chart of corrections for your ammo box lid or rifle stock.