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I have no4 mk2 with the mkI rear sight (thumb wheel adjusted) I noticed the sight leaf doesn't always move between the detents of the adjusted knob. Especially when you change direction from up to down.
Is there a way to improve or repair this back lash?
is it just nature of the beast?
Also approx how much of a change in minute of angle between the detent spots on the adjusted knob?
It sounds like there might be dirt in it. I'd say take the sight off and flush it really well with a penetrating oil. Working it as you go.
The clicks are in 25 yards (22.86 meters) increments.
On a 1300 yard sight, on a standard length No 4 rifle, each click moves the point of aim 1 inch at 100 yards - so the sight has more or less "1 MOA" adjustments.
If there's backlash between the screw and the nut then you'll have to replace them. If it's between the round nut part and the cursor slide, then we used to peen the front and rear edges of the nut to tighten it up in the slide. If it is in the slide and the leaf then 'adjust' the cursor slide so as to be a tight fit on the leaf.
In short, you've got to strip the sight down.
As Max Smart says, the increments are APPROX 1MoA but not exactly. Get some advice before you strip it as you WILL loose some balls - if you'll excuse the phrase
Another source of backlash I've found more than once is the little elevation screw retaining pin worn about half way through.
Quote:
Originally Posted by Peter Laidler
Been there, done that. To prevent the unlucky event, dismantle the sight with your hands plus sight inside a robust plastic bag. It may look daft but it works. Even trickier is re-assembling the sight, which requires firm but gnat-sized fingers, something I have not yet managed to achieve. The danger moment is when you are trying to finagle the ball into position so that it clicks. Any unsteady movement at this point results in the ball pinging out at great speed, never to be seen again. I am quite serious about the plastic bag!
Quote:
Originally Posted by mac1911
An elementary technique to compensate for backlash is to always make the final adjustment in the same direction. Especially as the typical combination of backlash and "stiction" means that first of all it doesn't move at all, then it moves with a jump, too much.
Example: you need to come up 10 clicks on changing range. You make a couple of test shots, and see that the POI is now too high. You need to come down two clicks. So you lower the sight two clicks - and nothing happens! Because the sight has two clicks of backlash and the leaf is stuck! So you lower another two clicks - the leaf jerks down the two clicks plus (at least a part of) the backlash - and the shot is now far too low! So you go up a click - nothing happens---- etc etc.
If you do this sort of fiddling during a competition you might as well stay at home. Even in a practice it is exasperating.
The trick is: you went up 10 clicks, and need the POI to be lowered by 2.
So you lower the sights by, say 5 clicks (the amount must be larger than the intended adjustment + backlash) and then go up 3 again.
By approaching the final position always from the same direction you have outsmarted the backlash!
BTW, anyone who uses machine tools knows this trick, which is useful for lathes, micrometers (yes, they can have backlash too!)... in fact anything requiring precision positioning.
In fact, you may find that using this technique means that you can achieve reliable results without having to dismantle and refurbish the sight.
One or two I've managed to take apart. Others you can pound on the pin and just end up with a bent punch. Some just don't want to move.