How to see if my NV rifle scope is losing zero when I change batteries: Your questions answered

More of your questions answered from fox calling to deer stalking at night and minimum calibres required.

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Night vision

Question: How can I test to see if my night vision rifle scope is losing zero when I change batteries, as I can’t confirm why I’m missing shots and want to be sure before I send it back? 

Chris says: This is quite a common question. Unload and make ‘safe’ your rifle, place it somewhere with the longest view possible and rest it on a solid surface as securely as possible because any mechanical movement you apply to the gun will destroy the results of this test.

Once it’s lodged as securely as possible in position, take note of the scope’s exact point of aim. Then, turn it off, turn it on, charge it, change batteries, update firmware, whatever you like really. Then, turn the sight back on and see if it’s still pointing where you ‘aimed’ it. Is it still pointing at the same spot? If so, it has not lost zero and you can be confident it’s something else.

In truth, this test, when done still attached to the rifle is full of potholes so I use a Picatinny rail bolted to my workbench, aimed at a wall at the distant end of my road. With any scope or night vision device (not attached to a rifle), I can repetitively dial and test mechanics and electronics without any fear that the device itself is moving and generally speaking, this rules out the optic.

Scope mounts and mounting systems are nearly always at fault and it only takes the tiniest movement within what should be a fixed mechanical system to affect your zero.

Most people think recoil is just linear impulse, but the rifle’s action has induced bending forces applied to it by the resonating barrel whipping around in fractional quantities. Imagine what this bending does to the screwed-on Picatinny rail, or individual rings, or night vision mount, especially if it’s on its rearward extension bar.

Yes, zero can be lost easily in these scenarios just like it can from being laid across the back seat of your car and getting heavy bags dumped on top and sadly, a lot of poor quality aluminium mounts and steel fasteners are creeping into our world which only make the problem worse – so check everything.

To give you an example, I can mount a scope to this test rail and apply lateral forces to it and its mounts, deliberate brutality you might say, (within limits). Does the scope still point where I aimed it? I have had more that one setup plasticly deform (losing zero) with little more than a bump similar to that of a rifle being flipped onto its sling over your shoulder.


Question: What’s the best caller to use for foxes? Is a mouth caller better than an electronic one?

Mark says: Both mouth callers and electronic callers each have advantages and disadvantages! An electronic caller such as the FoxPro firstly gives you a massive selection of high quality sounds at the touch of a button and allows you to replicate sounds that would be impossible to make with a mouth caller.

The other advantage is that being remote controlled you can place the caller in front of you some distance which means a fox’s attention is towards the caller as it approaches and not towards you, therefore it’s less likely to spot any movement as you prepare for a shot. The downside is that it runs on batteries which go flat and it’s a fairly bulky item to carry.

A mouth call has the advantage that it’s cheaper than an electronic caller and small enough to keep in a jacket pocket or hung on a loop around your neck.

These can be very versatile for volume and pitch allowing you to adjust your calling to any situation. But actually you don’t need either. You can learn to call from the back of your hand, which with a little practice can be extremely effective.


Question: In my locality there are numerous road traffic accidents involving deer. Is it legal for me to shoot them in the dark?

David says: Under Section 3 of the Deer Act 1991 it is unlawful to kill deer of any species at night. By night I mean from one hour after sunset to one hour before sunrise. Even attempting to do so is on offence.

There are exceptions to this law. First, under Section 6 of the Act it is not an offence to kill or take a deer at night to prevent it from suffering through injury or disease. Section 6 also allows a dependent orphan deer calf to be killed if it has lost its mother e.g. in an RTA. In such circumstances a trap or net may be used to take it.

In practice the law set out in these sections is most likely to be applicable after RTAs. In addition to creating the exemption from the general law that allows the night shooting of an injured deer any reasonable means of killing such a deer may be deployed and there would be no offence if a shotgun, rifle (not being a deer calibre rifle) or knife was used.

The test of whether a deer is seriously injured is one in which the person who has the means of killing it must decide whether he or she is putting it out of its misery. Is the proposed killing merciful in all the circumstances? There are other limited exemptions from the law mostly relating to the prevention of damage to crops and trees. 


Question: I see there is a product on the market that is meant to act as an attractant for foxes and I wondered if you had tried it out and if so what were the results?

Mike says: I suspect the product you are talking about is the fox attractant sold by Rob Crampton of Best Fox Call fame. I have used this on many occasions and in common with most things where foxes are concerned sometimes it works, sometimes it doesn’t!

From what I have learned when using it where you actually spray the ‘scent’ can be the difference between success and failure. Again, as with calling foxes, using the attractant works better sometimes than others. Without a doubt the most likely time it will work well is during the mating season when scent is very much in the forefront of a fox’s mind.

The big advantage this spray has is that it holds a fox up for long enough for a shot to be taken, when foxes scent mark, more often than not they only pause for a moment before moving on. When the spray is used they tend to sniff around the area for much longer.

What I’ve found is important is where you use the spray: foxes scent mark on places that to them are obviously significant, often isolated items such as large stones, telegraph poles in the middle of fields, mole hills and the like are chosen along with gateways and junctions where tracks cross. Select your spot and with a bit of luck your fox will linger long enough for a shot to be taken.


Question: I’m struggling to get my .223 rifle to shoot well past 200 yards, I get groups of around an inch at 100 yards but if I try to shoot further it doesn’t seem to be on zero anymore!

Mark says: If you are getting an inch group at 100 yards (or 1 MOA) then you would expect to get around a two inch group at 200 yards and a three inch group at 300 yards. Naturally you will notice your group will drop around an inch at 200 yards and depending on your bullet weight probably a good nine inches by the time you’re out to 300 yards!

You will also experience wind drift if you have a crosswind on your bullets line of flight. Also be aware that the further out you shoot the more pronounced any shooter error will be.

You don’t mention what scope you’re using, but if you’re using a night vision scope these can sometimes be difficult to achieve pinpoint accuracy with, depending on the unit you’re using. It may be worth testing some different ammunition too, as each individual rifle will prefer different brands – and be sure to match your bullet weight to the twist rate of your barrel.

If you’re unsure what bullet weight to use, you can search online for your calibre and barrel twist to find out what would be best.


Question: I am unable to get an MOA rail for my rimfire rifle and I want to start experimenting with long range, will higher rigs do the same thing as greater spacing from the action to the scope via a Picatinny rail? 

Chris says: Gaining more long-range capability from a scope is not helped by raising it from the action via a Picatinny rail nor taller scope rings, it’s about the angle at which the scope and action are allied together.

If you look closely at an inclined rail, 20 MOA (minutes of angle) is the most common, it will be effectively thicker at the rear, close to the bolt, than at the front, towards the muzzle.

This means the scope is effectively sloping downwards towards the muzzle. Some rifles show differing action bridge diameter and height which can sway this visual cue a little.

The internal mechanics, tubes and lens packages within the scope are what move up and down in this angular way (think of a seesaw) to alter the elevation of your bullet’s ballistics and consequently, the point on or at which it hits the aim point.

Although the height of the rings can have a very small effect on the exact range at which the bullet’s arcing line of flight intersects the single linear line of sight of the scope, it won’t inherently give you greater long range capability as taller scope rings just move the scope away from the barrel in parallel.

An inclined rail, mount (and in fact there are some paired rings that will do this) tilt the scope’s outer tube, just like the seesaw, so less of the tube’s finite internal mechanical adjustment is used up.


Question: What is your opinion on having a ‘close season’ for foxes. This seems to crop up from time to time and I wondered what your take is on this.

Mike says: This question has cropped up increasingly over the past few years and isn’t an easy one to answer simply because of the problems foxes can cause at breeding time. In most cases where any species of animals are given protection the protection period covers their breeding season, deer are a case in point.

The problem with our friend the fox is that during their breeding period they are at their most destructive, so protecting them at this time would be asking for trouble.

At the moment foxes – despite the considerable increase in the people shooting them – seem to be holding their population numbers well. So for the time being I think there is no great need for any form of protection, as to whether this will change at some point in the future, only time will tell.


Question: What rifles are deer law compliant in England and Scotland?

David says: Subject to the exceptions mentioned below in England and Wales it’s against the law to kill or injure any species of deer with a bullet or bullets fired from a rifle with less than a .240 or with a muzzle energy of less than 1,700 ft/lbs.

For most stalkers using readily available rifles and ammunition this means that the widely used .243 is the minimum calibre of rifle compliant with deer law.

An important exception introduced in 2007 permits the use of a rifle of not less than .220 and a muzzle energy of 1,000 ft/lbs for killing muntjac and Chinese water deer. Ammunition must be soft nosed, and expanding not solid.

In Scotland the law is different. Expanding bullets of a minimum weight of 50 grains fired from a rifle with a minimum muzzle velocity of 2,450 ft. per second and a muzzle energy of not less than 1,000 ft/lbs. are legal for use against roe deer.

In the case of other (bigger) deer, bullets of not less than 100 grains are required with a muzzle velocity of not less than 2,450 ft per second and a muzzle energy of not less than 1,750ft/lbs.

The law is different again in Northern Ireland with bullets of a minimum 100 grains being required. More exemptions relate to the use of otherwise non compliant firearms and shot guns when deployed for humane dispatch and crop protection purposes.

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