Changing No4 Rifle Foresight Blades.
For clarity the ‘Foresight Block’ is the part that the foresight blade fits into. This piece is a sliding fit over lugs at the muzzle of the rifle, and is secured in place by a taper pin which fits from left to right and passes through a groove machined across the top of the barrel. The foresight block (on all but the very early types of 1 piece foresights – rarely encountered) has a Foresight Protector fitted over it. These are a sliding fit over the foresight block and are held in place by a transverse screw which fits from left to right and passes through the foresight block.
There are 2 basic types of Foresight Block which are commonly encountered. The Mk1 Foresight Block and the Mk2 Foresight Block.
Types of Foresight Block
The Mk1 foresight block is what is termed a split type. There is a diagonal split vertically through the block and a screw at the front of the block which allows the split to open or forces it to close, to grip or release the foresight blade dovetail. Originally these were designed to be used with 'solid' foresight blades, however this was later amended and either split or solid foresight blades can be used with these. The 7.62mm L42A1 Sniper rifles almost exclusively used the split type of blade in a Mk1 foresight block.
The Mk2 block is what is termed a solid block. The foresight blade base is split through the dovetail from side to side (as per the Mk3 blades on the website) and these are reliant on the spring tension created in the foresight blade dovetail when these are compressed as they are driven into the dovetail in the block, to retain them in position. These blocks should only be fitted with Mk1* or Mk3 (Split Base) Foresight Blades.
Because a Rifle is a Mk1 does not mean that it will – or should have – a Mk1 Foresight Block fitted, any more than a Mk2 should or will have a Mk2 Foresight Block fitted. Although chronologically the Mk1 block came first, the Mk2 block was introduced into service long before the Mk2 Rifle was. Rifles would have been fitted with whichever was available when produced, and likewise when repaired or overhauled the only criteria in the majority of cases would have been ‘was it serviceable’
Tools and Aids
Special tools were provided for the user to adjust the foresight blade for windage. These were firstly the zeroing cramp (officially referred to as the ‘Cramp, Adjusting, Foresight, No3 Mk1 for No4 Rifles’ Part No CR29A) and the ‘Tool, Removing, Foresight Screw’ (Part No BC8796). The Tool Removing Foresight Screw was only required for Mk1 Foresight Blocks.
In addition to these a Drift (usually a ‘Drift, Armrs, No2’, but any flat faced drift of around 3/16” (2.5mm) diameter will do), a centre punch and small hammer, were required for actually changing foresight blades, and for marking and securing them in their final zeroed position.
In point of fact, more often than not, the whole adjustment process was carried out with only the hammer and drift, and if a ‘split’ pattern of foresight blade was fitted, even the tool removing foresight screw could be dispensed with on a Mk1 block - in most cases. The process of zeroing using a hammer and drift only requires a delicate touch, a degree of patience and some skill, but with experience and the use of common sense, is achievable.
Changing a Foresight Blade
It is not intended to cover the actual zeroing process here, however as part of this process, or should the foresight blade become damaged, it may be necessary to actually change the foresight blade. This process will be described assuming that a ‘live’ rifle is being worked on.
Before doing anything ensure that the rifle is UNLOADED and the live ammunition is not present in the magazine. Safety first!
It is first necessary to mark the position of the existing blade in the foresight block before removing it. On the front edge of the foresight blade base, in a central position, will be a notch or centre pop mark. There will be a similar mark (or marks) on the front flat of the foresight block. If you are lucky there will only be one central notch on the foresight block, and if you are very lucky, the notch on the foresight blade will line up with this mark. If this is the case you need do nothing else at this stage.
If the notch in the blade does not line up with the notch on the foresight block, then using the centre punch or a scriber, make a mark on the foresight block in line with the notch on the blade. NOTE; all marks should be made on the foresight block NOT the foresight blade!
Once the blade position has been marked it can be tapped out to the side using the hammer and drift. If a Mk1 foresight block is fitted, and especially if it has a ‘solid’ blade, the foresight screw should be loosened or removed first (put it somewhere safe, do not lose it!). In many cases, once the screw is undone, the blade can simply be pushed out with the drift.
Replacement is the reverse procedure, however to initially seat the new blade it may be advantageous to remove the foresight protector first by removing it’s securing screw and sliding it off of the rifle to the front. Position the new blade so that it’s notch lines up with the mark that you made on the foresight block, and if you have a Mk1 block, tighten the foresight screw to secure the blade.
Safety First! Unload and clear the rifle before doing anything. If you are making adjustments on the range then resist the temptation to just apply the safety because ‘it’s only a little tweak’ – that is how people get maimed & killed!
When using the hammer and drift, ensure that the rifle is held securely and supported. The ideal is secured in a vice with soft jaws, however if doing it on the range get a strong friend to assist and rest the foresight block or foresight protector on a solid base such as a block of wood.
The drift tip should be positioned so that it is bearing on the actual dovetail part of the foresight blade as low as possible. This minimises the risk of slipping off and causing damage and ensures that you use the energy applied as efficiently as possible. Never use the actual blade portion of the foresight blade to move the foresight across.
If a foresight blade has any damage when you remove it, discard it then & there. If you do not it will get mixed up with the good ones and come back to haunt you later!