Target Sports

TARGET RIFLE BASICS: REARSIGHT FUNCTION

Created on 29th May 2009

CHRIS WHITE explains the basics of rearside function, including how to zero the rifle

WITHOUT GETTING too much into ballistic theory, we need to appreciate that as soon as the bullet leaves the end of our rifle barrel gravity pulls it toward the earth. If our rifle sights caused the centre of the bore to be aligned with the target the bullet would fall to earth long before it got to the target.

Therefore the rifle has to be elevated so the bullet is projected in an upward direction from where it is pulled downwards by gravity. This upward elevation of the rifle has to be arranged in such a manner that on its downward path the bullet strikes the target in the desired place.

That is pretty straightforward. It is also, I hope, obvious that the ‘line of sight' and the bullet's path should intersect at the point of impact. This is called the rifle's zero. If they don't the rifle is ‘out of zero' and steps need to be taken to zero the rifle. This is very important if we are to hit a small target (like a V bull!) and we will deal with zeroing in some depth shortly.

At the moment we need to understand why the rifle needs to be elevated.

Understanding elevation

The relative configurations of the foresight and rearsight are arranged in such a manner the muzzle of the rifle is raised. That is that the foresight must always be lower than the rearsight and thus the line of sight is not parallel with the bore.

In its simplest form a fixed rearsight such as on a classic sporting rifle will allow the rifle to hit what it is aimed at, at one specific range, and that range is set at something where an actual error in the rifle's sighting or the shooter's range judgement would not move the point of impact far enough away from the point of aim to make any practical difference to the lethality of the shot.

Initially military firearms followed the same path but as accuracy and sophistication improved it became feasible to engage the enemy at longer ranges and therefore the rearsight had to be adjustable so that the elevation set on the rifle was compliant with the range at which the enemy was to be engaged. Vertically adjustable rearsights have, therefore, been around in abundance for the best part of 200 years.

While it may not be politically correct to think like this, a sighting system that permitted a combat soldier to hit an enemy somewhere between the belt buckle and the chin at 200yd would be perfectly adequate for the job in hand. Hitting a 2.1" V bull at the same distance requires infinitely more sophistication.

Many factors can cause the rifle's point of impact to vary. Therefore, not only has the rearsight got to be adjustable to allow shooting at different distances, it needs to be adjustable to ensure that on a given day the line of sight of the rifle and the bullet's path do intersect in the middle of that V bull.

To that end, target rifle rearsights in the UK are adjustable in increments of one quarter of a minute. This is pretty universal but Australian Central Sights are adjustable in one thirds of a minute. These minutes may be true minutes or ‘rifle' minutes. All this has already been covered in detail, early in the series and is not relevant to the matter in hand.

Let's step aside from NRA Target Rifle for a minute and consider the archetypal smallbore shooter who always shoots on an indoor range at 25yd, probably always on the same range and often with the same brand of ammunition. He has no need to know what his sight setting is since it is always near enough the same. So he lies down with his sights set at where they were last time he shot and fires a few sighters, making minor adjustments to the sights to move the centre of his group into the centre of the bull.

That's fine under these circumstances. If he ventures to 50m or 100yd he knows how many ‘clicks' to come up: hence the far away stare as he counts 36 clicks, or whatever.

The novice Target Rifle shooter soon learns the practical difficulty of this when he goes from 300yd to 1,000yd and has to count 120 or so clicks!
Know your vernier!

All Target Rifle rearsights have vernier scales so that we can read our sight settings to a quarter minute. Reading verniers is one of those things that is very easy when you know how to do it and a complete mystery when you don't. Demonstrating it can be hard. Trying to explain it in print is even harder. If you can do it you can skip the next bit: if you can't then read on. Smallbore shooters who have British rifles or have ‘full bore' sights on their rifles can also benefit from understanding this.

Film buffs may remember Humphry Bogart's words as Captain Queeg in The Caine Mutiny, "There's four ways of doing things, the right way, the wrong way, the Navy way and my way!" There are various coping strategies adopted by shooters who can't read a vernier. I do not approve! You must at all costs learn to read it. If you don't grasp it read this and the next article over and over until you do. If you still don't, then please get someone who does to show you. This is very important!
All vernier scales work on the same principle but may have different increments on the vernier. Some old rifle sights for Long Lee-Enfields, for example, may also differ. The principles of reading all verniers are the same. All Target Rifle sights have verniers based on increments of five minutes. All verniers have a fixed and a moving scale. Now down to business. Go and get your rifle, as we need to work through this together.
One scale is the rifle's elevation scale and it has graduations on it in increments of five minutes and multiples thereof and (probably) numbers at 20 minute intervals. The other scale is the vernier and has six graduations on it. One scale moves as the sights are moved and the other remains fixed; also one of these scales will be attached to the sight by screws and its position is adjustable. Depending on the sight manufacturer it may be the fixed or the moveable scale. It does not matter. The vernier scale has a point on it marked zero and another marked five.

When the elevation set on the rifle is zero, five minutes, or some multiple of five, the zero division will coincide with that reading on the main scale and the five-minute division will coincide exactly with another graduation.

Now take your rifle and set the two zero divisions together. This is zero and the line marked five on the vernier scale should align with 20 on the elevation scale.

Move the sight up until the zero line on the vernier scale coincides with five minutes on the elevation scale. Now there are five minutes on the rifle. The vernier zero coincides with five, and five on the vernier coincides with 25 (it doesn't actually matter what it coincides with as long as it coincides with a full incremental division on the elevation scale).
Now set the elevation at 20 minutes. As a check look at five on the vernier, it should be opposite 40 on the elevation.

This is basic and should be easy. There are no problems setting your sight to five, 10, 15 or 20 minutes, or indeed any multiple of five. Next time we'll progress to any chosen setting.

TARGET RIFLE BASICS: REARSIGHT FUNCTION

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TARGET RIFLE BASICS: REARSIGHT FUNCTION

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