Ok. Sat and composed my thoughts a bit..
So a chronograph has two coils set up a few inches from the muzzle. They measure the disruption in the field between them.
Because the magnetograph hangs from the muzzle, the coating (gun bluing) may spread the field intentionally created by the designers. Since a copper jacketed round may have a current induced into it. There may be an effect on accuracy. Testing a jlead unjacketed round with this instrument may help to evaluate this.
Call it the particle accelerator effect..
Fodder for for the gunwriters..
I don't see how the bluing plays any part in this. The Magnetospeed sensors are forward from the muzzle, and triggered by induction caused by the metallic bullet travelling past each of them.The barrel material has nothing to do with the measurement. Call it the "innocent bystander not affecting the outcome effect", perhaps?
