[Ron Wood]

You guys are probably going to laugh me right off the planet, but here is my take on witness marks. I have never seen the utility of striking a mark on the barrel/receiver after they have been assembled. What purpose would that serve, other than as Viggo stated to indicate that a part had been removed and/or if the part is removed to assure that it is reinstalled in proper alignment?

I think they might more properly be called “index” marks. I believe that after final machining of the receiver fork, a mark was placed on the bottom forward edge that denoted the exact “bottom dead center” if you will. When the barrel is machined, the front sight block is broached from the forward barrel band and then a mark is struck on the rear flange exactly 180Ã?º from the vertical mid-line of the sight block (or exactly perpendicular to the horizontal plane of the sight block if you want to look at it that way). Once the barrel has been finish machined with the threads cut and the flange formed, the barrel is trial fitted to the receiver, turning it down tightly but not with a heavy torque. The index mark on the barrel should line up within a predetermined number of degrees or linear displacement from the index mark on the receiver. Given good manufacturing controls, I would guess that proper displacement was achieved better than 90% of the time without further machining of the flange. If the preliminary alignment was off, the rear of the flange was either machined a bit further to bring it into tolerance or discarded if it over-rotated.

Once it was determined that the index mark displacement was within tolerance, the barrel was properly head-spaced and the extractor groove cut, again using the index mark as a guide for proper placement. The barrel was then reinstalled and given a final torque to bring the marks into alignment. This assured perfect alignment in the vertical plane of the mid-line of the receiver and barrel, and obtained a solid mechanical compression fit of the barrel to receiver.

I further support this hypothesis by the observation that the frame serial number is applied prior to finish sanding and bluing. However, the barrel markings are applied “through the blue” to match the barrel to the frame after the barrel/receiver assembly has been completed and blued, thus giving rise to the “halo” effect on the barrel markings that is not found on the frame.

The foregoing I believe is a reasonable explanation of the marks. I would address the possibility of a “proper” misalignment by considering that the compression fit was sufficiently strong to permit a slight rotational adjustment of the barrel during test firing to adjust the front sight for windage and bring the shot group to center. Provided the adjustment was very minor, probably less than the width of either index mark, the compression fit would not be compromised. I would further suggest that quality control in the machining and assembly processes would make this adjustment unnecessary for all but a tiny fraction of the weapons produced.

OK, open fire.