Zeroing Windage on an Aldis No3 Scope

[Jacob]

Hi all,

Does anyone know how (or if) windage can be zeroed on an Aldis No3 scope? I have found instructions on the No4 but cannot seem to find anything regarding the No3. Any diagrams or notes on how to do it would be much appreciated!

Additionally, if anyone has a grub screw for the objective cell holder they would be willing to part would I would like to buy one.

Information

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[Roger Payne]

Hello Jacob. It depends whether you have a third pattern scope that is modified or not. As originally issued (typically with Holland & Holland & Purdey mounts) there was lateral adjustment on the mounts so no lateral adjustment was necessary or provided on the scopes themselves. However, many were modified to incorporate an adjustable prism cell in the objective end of the scope where the scopes were destined for use on rifles with mount systems that did not possess lateral adjustment facility, hence the need. The scopes are easily distinguishable in that the 'early' non-adjustable types have an objective housing that is only marginally greater in diameter than the scope tube, whereas the prism fitted scopes have a noticeably larger diameter objective housing. When the cover is unscrewed from this housing you can readily see the radial lines of the prism cell surrounding the objective assembly. Adjustment of the cell by one of these radial line increments moves the POI by 5 inches on a target (at 100 yds I think, but speaking from memory on this). However, the slight movement of the prism this entails also causes some movement in the vertical plane, so you may need to readjust your range drum.

There is a thread that I think is still current on this page in which I managed to get some prism cell brass covers made both for myself & the OP who needed one. I think there are photo's that might be helpful to you, as only prism modified scopes take the threaded brass cover as illustrated. That should let you know which type of scope you have.

[Surpmil]

I think you'll find Jacob, that the screw(s) which hold the objective cell from rotation on the scope tube are not in fact grub screws but very fine countersunk oval heads. The thread form, pitch and dia. are unknown to me, but close to 10BA or smaller IIRC.

If the objective cell female threads have worn to the point where the cell is no longer a close fit when the locking screw holes align, you could try a sealant of some type or brass or copper foil applied to the male threads of the scope tube to "take up the slack".

Roger has covered the adjustments, and all I would add is that if you have the prism cell, make up the correct tool for its adjustment from sheet steel as per the diagram in "Instructions for Armourers 1931".** I believe the dimensions are different, but the general idea is the same.

If and when you get to the point of attempting to turn the prism cell, some discrete use of heat and or a suitable lubricant may be necessary after a century of sitting, and unless the movement is very smooth and relatively easy, best done off the rifle so that a proper grip can be had on the object cell and the adjusting tool, not on the scope tube as then all the rotative force will go onto those very fine screws mentioned above! Be very careful and patient as over-exertion or a less than ideal grip can cause the tool to slip and damage the slots in the brass ring, at which point you're up the creek without a paddle!

** I see on checking that I was mistaken; there is no drawing of such a "key" in the 1931 Instructions for Amourers, only an end-on drawing showing the prism adjustments on the Patt.18 scope. However, the design of such a key or tool is obvious: the thickness to match the width of the slots as precisely as possible, and the edges to be carefully stoned smooth and slightly radiused so that there is minimal scraping of the female threads locking rings turn in. A shoulder on the key or tool is a good idea as it aids placement and helps to prevent slippage.

[Jacob]

Many thanks Roger and Surpmil!

I have had a look at my scope and it appears to be an unmodified model. I have a Purdey mount setup on my rifle with the adjustable base which I have maxed (or so I believe) to the left (the left edge of the front mount sitting about 2-3mm to the left from the centre line of the front base). This still leaves me with the need to aim off about 24" to the right at 100yds to hit the centre of the target (when aiming at the centre, the shots land off to the left as you would expect with a left side mounted scope). Will the base move anymore or is that usual for the amount of adjustment? I'm not expecting incredible things out of the rifle so I'm not that bothered if I have to aim off but would be nice to get it a bit more 'zeroed' if possible.

[Nigel]

When correctly zeroed the shots should strike about 2 inches to the right of the point of aim. This parallel aspect should be maintained at all distances. Whilst it is possible to obtain a point of aim / point of impact zero this will only happen at one distance and any greater distance will see the the point of impact diverging to a greater and greater extent as the range increases. It was the same with the Bren gun!

[Roger Payne]

The Sniping pam of November 1917 does say that (& this must be an approximation as various different types of offset mount systems were in service at the time) the scope & bore should be parallel, with the scope offset 1.5 inches to the left of the bore. This results in a consistent aim off at all ranges. I'm responding off the top of my head & can't remember without digging out the pam what it said (if anything) about the vertical plane.

[Roger Payne]

Against my lazier instincts I got up & had a quick shufty........see the para starting 'Offset'.....My words aren't exactly what is written but I think the general idea is the same.

[Surpmil]

Someone blundered there and not just once. Rather stupid advice to suggest that 1.5" inches doesn't matter beyond 100 yards as 1.5" is about the width of a German loophole plate's aperture.

The second paragraph contradicts the first and the paragraph below the two highlighted is a lot of rot as well.

Odd the use of fine brushes is not mentioned for removing dust from lenses. Of course in the cold and wet of France and Belgium condensation was the problem for most of year.