IHC Barrel Punch Mark

[Durango56]

What time frame/serial number did IHC start using punch marks on barrel?
Thanks

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[Bob Seijas]

From the start, it was an Ordnance requirement. The barrel was proof fired when made and marked with a P, then proofed again when installed. Specs said a prick punch was to be stamped in the loop of the P, but that exact location was often ignored. IHC put the punch between the LMR and the drawing number, it's characteristic.