Malamute, a given barrel has the same harmonics of its resonant frequency for every round fired; the barrel's metal and profile stays the same for each shot. Old, new, military, commercial, handloads; doesn't matter. Problem's more often powder deterioriation causing wide velocity spreads or too small of bullet diameter for your barrel as well as primers gone erratic. Occasionally, the seal in the case mouth's changed its grip on the bullet and muzzle velocity's all over the scale.
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