Decide whether to true BC or muzzle velocity

Verify everything that should not move. Confirm target distance, zero, units, sight geometry, drag model, and environmental conditions before changing velocity or BC. Protect a trustworthy chronograph value. When muzzle velocity comes from reliable chronograph data for the current ammunition and conditions, prefer investigating or truing drag behavior before rewriting velocity from drop. Question velocity only with evidence. Consider velocity truing when chronograph data is absent, suspect, or clearly inconsistent with repeatable observations after the other inputs are verified. Change one model input at a time. Record the observation, apply one correction, recalculate, and compare the entire useful curve. Simultaneous MV and BC changes can hide which assumption was wrong. Re-validate at other distances. A trued value is a proposal until it improves agreement across more than the calibration distance.

Truing cannot rescue poor evidence. Do not true from an uncertain impact, unknown conditions, unstable zero, wrong projectile, or incorrect target distance. Fix the evidence first.

Truing is a modeling decision. The profile controls can preserve corrected inputs, but they cannot decide which physical assumption caused a disagreement. Keep the measured source, prior revision, and reasoning.

Expected result. The adjusted profile has a recorded reason, preserves trustworthy measurements, and improves agreement across multiple distances without unexplained side effects.