Springfield Armory used a punch mark on the 1911 pistols when the first ones went back through for rebuild. Later they used the SA stamp. When Springfield was building the National Match pistols in the 1950's and 60's they again used the punch mark, but it does not appear on every NM pistol.
Can't speak for the 1903 barrels, but all the 1911 pistol barrels were proof fired in a fixture before they were assembled into a pistol, where they were proofed again.
These punch marks are on a 1961 Springfield NM pistol. The P proof on the frame and slide was from the original assembly of the pistol.