Depth of scope mounting holes?

[Rayleigh_Scattering]

I seek wisdom.

I have recently acquired, by trade, a 1918 Mk III*.

It looks good, but you can really see the stresses of the Great War on the production line. That's the nature of milsurps, no worries, and I'm sure it did what G.R. wanted it to do.

A scope mount was installed at some point (very recently) by drilling and tapping. I unscrewed it to inspect the workmanship.

The location and alignment of the holes drilled for that mount is good. The threading is perfect, and the holes line up exactly with the holes in the mount rail.

I have a question about the depth of the holes. The tail of my caliper wouldn't fit, so I used a handy hex key to illustrate:

The measured depth of the holes is 9.2mm from the tangent, although there's probably +-0.2mm on that due to the squishy keratin tools I used as reference markers.

I don't know the internal construction of the receiver in this area, but the hole looks to be well through the receiver ring (which is relatively unstressed in this area) and a fair way into the barrel tenon at the chamber where all the psi happen.

Can anyone else with a similarly drilled MkIII take a quick measurement of the drilled hole depth for comparison?

 

[Potashminer]

The scope mount holes were not drilled by the MkIII factory - done after it left military service and got into civilian hands. I would guesstimate that at one time or other I have owned about 50 bolt action rifles that were factory drilled and tapped by the rifle manufacturers - I have never seen one drilled and tapped into the barrel - 90% or more you can see the barrel tenon threads through the front hole on receiver ring, the rear hole is almost always a through hole into a bolt lug cavity.

 

[woodchopper]

I have one that is drilled all the way into the chamber

just as a test I have fired it that way

the hole is far enough back and small enough that the web of the cartridge is able to maintain the pressure

however I feel that it is very unsafe

 

[Rayleigh_Scattering]

With a bit of searching I acquired, locally, a second 1918 MKIII* with exactly the same scope mount installed in it.

The two drilled holes on that copy are about 6mm deep.

This second one will likely take the place of the deep-drilled one in my plans.