Need help adjusting front and rear sights for zero on No4 MK1/2

[Patrick Chadwick]

I am not using the backsight as a zeroing medium. I am using the front sight.

Please do not take this as a personal comment, but as practical observations based on experience with long guns from a Napoleonic vintage musket through to a modern 6mm BR shooting machine, and a lot of what came between. That means everything from a howitzer-like trajectory to a very flat one indeed, and I have given up trying to make precision calculations for range changes, being happy if the correction puts the bullet in the black at the altered range. I realize that I am also partly repeating what has already been put quite precisely and in detail, so I shall put it quite straight and simply.

Be CAREFUL to compare like with like. If you are using a 6 o'clock hold, then you are applying a vertical offset of half the diameter of the target black between your actual POA and the intended POI.

If, for instance, you shoot with a 6 o'clock hold at 50 and then move the same size target out to 100, then the black now subtends half the angle in your sights compared with 50, so you are raising the POA by an amount equivalent to half the difference between the bottom of the black and the center at 50. That is quite a lot - in fact half of the apparent size of the black if you double the range - and this effect alone often means that a rifle that is in the black at 50 will also be in the black at 100 without any further adjustment. The POI may be higher or lower, depending on the height of the sights and the trajectory of the bullet. The same effect applies if you go from 100 to 200 with the same size of target black. Even if you use proportionally scaled targets to produce the same apparent size at all ranges, there is still the following effect:

CONTRAST CHANGES WITH DISTANCE*. Your judgement of the correct aim for a 6 o'clock hold is affected by the contrast between the blade, target white and target black. So shooting one-hole groups at 25 yards will still not enable a perfectly calculated correction for 200. And if you are using a center hold (generally not advisable with a blade foresight) then the contrast effect is even stronger.

Use 100 if you can, 50 if you must, but forget 25, where the "uphill shooting" deviation caused by the sight line being above the barrel center line is quite extreme.

Be GLAD that you have a +.075 foresight blade. I wish I had a couple myself. The vast majority of old service rifles were zeroed for a longer range and/or have foresights so worn down that you can hardly get on target at 100. As has been pointed out, the higher foresight gives you room for adjustment if/when you try out different loads. DO NOT SNOOKER YOURSELF BY REDUCING THE BLADE HEIGHT TO SUIT ONE LOAD AT ONE RANGE. You have a height adjustable backsight. Use it.


*And lighting conditions!