No.4, No.5 and No.8 rearsight thread pitch

A friend recently gave me a No.8 rearsight that I'm refurbishing. It had 3 clicks of backlash and the range markings were almost unreadable through 65 years of accumulated use.

I noticed after stripping it that the elevation adjusting screw thread was visibly different from the No.5 rearsight I have lying around. The shank is thinner and the pitch is tighter. Until now I hadn't realised the threaded part of the No.5 screw is much shorter than the No.4 as well!

The picture below isn't very good but you can just about see the difference between No.8 (below) and No.5. Why were they so different, though? Surely the only change that needed to be made was putting different markings onto a common leaf assembly?

https://www.milsurps.com/images/impo...33865959-1.jpg

You're dead right. But that's the way they did it. But due to the barrel length and difference in muzzle velocity they - so said - wanted to retain the 1 click = 1 minute of angle formulae between the two rifles. Forget the No8 here because by this time, common sense had prevailed. Better still, by the 50's and onwards, common sense had also prevailed with the No5 too and most of those 'common' components such as the bolts and foresight blades, sears and trigger guards had been made fully interchangeable. This is reflected in the updated No5 parts lists

Can't say much about the No.8, but at least on these two examples (No.4 & No.5, original sights), there appears to be a difference in screw diameter and pitch. Given the slightly coarser thread on the 800-yard sight, the "click value" would be some 10% greater than the 1300-yard sight if both were mounted on rifles with the same sight radius - except for the fact that the 1300-yard elevation screw is double-threaded, giving it an effective pitch approximately double that of the single-thread 800-yard screw.

On measuring the two sights shown, each click of the No.4's sight moves the slide .008" - vs. .0043" on the No.5's sight. Consequently, the 1300-yard sight gives very close to 1.0 MOA per click with the No.4 rifle's 28" sight radius while the 800-yard sight has a click value of ~0.66 MOA with the No.5's 23" sight radius and would yield ~0.55 MOA on a No.4 rifle.

https://www.milsurps.com/images/impo.../2943p13-1.jpg

From a No.8 .22 trainer (sorry about the lint been on a shelf for a while)

Thread 3 also shows how they ensured the No4 and 5 screw and nut were machined in a way as to be totally non interchangeable as sets (nut and screw) and when fitted to the sights. (But you could fit a No4 screw and nut to a No5 sight - which we did anyway because the No5 parts were soon obsolescent and NLA anyway).

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Originally Posted by CINDERS

No.8 backsight

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I had forgotten what they looked like. I had a couple but couldn't remember their marking...that's right, they only had three. I think I changed mine for a Parker Hale 5C...?

That would have been a better deal as the 5C's are getting good money nowdays $270 plus

Quote:

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Originally Posted by browningautorifle

I had forgotten what they looked like. I had a couple but couldn't remember their marking...that's right, they only had three. I think I changed mine for a Parker Hale 5C...?

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Don't forget H up the top! We used it a few times in the ATC for the Green Howards Country Life match, to save the poster printed targets. From memory it moves the point of impact 27" higher than the normal 25yds setting.

Quote:

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Originally Posted by CINDERS

the 5C's are getting good money nowdays $270 plus

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At the time they were probably $75 CDN and I had been given this one on a FN C1 body cover by an armorer. It had been done for a rifle team whim to see if they could make the FNs some special target rifle within the unit. Rules at Bisley outlawed it of course. I used that sight on everything LE from one time to another...and every FN I had.