WW1 'Periscope Prism company' sniper scope???

[lmg15]

Some very good insights there that get me thinking.... I have had a bit of experience with the manufacture of the front mounting blocks for the Patt.18, and as a result have had to consider some of these things from both practical and theoretical points of view.

It is hard to know all the steps that PPCo considered in the evolution of the Patt.18 mount system, but I think that the theoretical failings of the German shallow claw system (as you very cogently spell out above) were understood by PPCo. The ability to use the Aldis lateral adjustment prism gave them the opportunity to make the scope and rifle mounts as rigid, simple and solid as possible, while still allowing for quick detachment.

That brings us to the question of whether the PPCo system was the best in practicality and execution, but without some objective evidence, it is hard to say whether the Patt.18 system of mounts was a practical improvement over the German shallow claw mounts. That would probably come down to things like no wandering zero and repeatability (ability to keep MPI after when the scope is mounted/dismounted from the rifle over and over), when compared with its German counterparts. Maybe PPCo had such faith in the rigidity of the Patt.18 system and its corresponding repeatability, that the PITA prism adjustment was something not required often enough to be a real PITA?

In terms of the practicality of execution from an engineering perspective, The level of commitment to precision in the PPCo mount system is very high, given that it is also designed for a high degree of interchangeability between rifles and scopes (notwithstanding the scopes still being serial numbered to the rifles). This means that any significant factory of field hand fitting is not on the agenda, as opposed to almost every German WWI sniper rig I have seen (maybe with the exception of the late war Goertz semi turret system).

So with that in mind, the use of the transverse pin in the front rifle mount must allow the scope only one degree of freedom when it is attached, being movement backwards and forwards. This has to be done with extreme precision in terms of eliminating any vertical movement whatsoever, so its diameter, in turn, has to be a very fine tolerance fit into the notch of the scope mount claw. The rear scope mount is locked rigidly into the rear rifle mount with a slight interference fit with the semi cylindrical locking catch / cam (it should tighten up a little and the thumb lever is rolled over to lock in the rear scope leg). Hence you have complete rigidity with the scope locked in both vertically and horizontally.

The lateral degree of freedom is addresses by having fine tolerances and large bearing surface areas between the front rifle mount slots and the claw blades. Similarly fine lateral tolerances on the rear mounts too.

So, that's the theory, but how practical was it? Well, having tried to make a set and measuring pins and slots to the point of near insanity, I can vouch that the fine tolerances required were executed well by PPCo (and not necessarily by me). Also, having done one pair of front rifle mount blocks, I am pretty certain of the exact manufacturing sequence required to achieve the required outcome, and for a well set up shop, it is eminently do-able, with one pair of identical blocks coming out of each set of operations.

So that is my insight from personal design and manufacturing experience.

As an aside, I cannot understand why the Accumounts versions of the rifle blocks are so poor when they could be much better for just a little more effort. That notes that you cannot fit an original Patt.18 scope onto the Accumounts front block because the pin diameter is too big, and has to be ground out in the middle to fit it onto a receiver ring. The Accumounts rear rifle block has paid vague homage to the original, but in all other respects has gone completely free-style. The Accumount scope rings are also not too good, as they do not have the rounded profile. I accept that it is diabolical to get that round profile for the home machinist, but easy enough on an industrial NC machine. Attempting to rectify the Accumounts product is also fraught, as they have used extremely hard steel that resists every attempt to put even a scratch on them.

So I am not defending the mount design or the HEnsoldt scope per se, but I can at least see why they did what they did on 'optimising' the German Hensoldt Dialyt overbore claw mount scope given the mindset they were in.

Having a look at TBSp.73, IDS mentions the CISA decision process in favour of the Hensoldt scope, but the SAC minutes (that I don't have) probably tell us a lot more. IDS also makes the same mistake(??) as me in assuming the Hensoldt scope was on a captured German rig, but he does go on to elaborate to remove doubt that it was indeed a German rifle:

"in mid 1917, a captured German sniper rifle with a light Hensoldt telescopic sight on detachable crawfoot mounts became the inspiration for the assembly of a Pattern 1914 sniper rifle, upon which was mounted an Aldis telescope in the overhead position, using similar mounts. This combination rooved successful enough to warrant its being sent to France for assessment trials, along with the German rifle".

Showing my ignorance again, the SAC minutes talk about the Hensoldt scope being on a "short rifle" (which I assumed to be a Kar98a), but further references to "short rifle" left me under the impression they were talking about the SMLE (vs the MLE/CLLE). The Hensoldt Dialyt 3X being small and light would certainly be well proportioned for the Kar 98a. Can any further light be shed on this?