Accidental Discharge

One of the commonest causes of shooting fatalities is the accidental discharge of a weapon which was loaded and at full cock, and not a single shooting season passes without some such fatal accidents being reported. Anyone carrying a gun may stumble and drop his gun, when the blow which the latter receives on falling is liable to jar the lock or locks off, and thus cause an accidental discharge. The possibility of this happening is almost too well known to need emphasis, but it may not be out of place to explain very briefly the general principle on which all gun, rifle and pistol locks work, so that the reader will be able better to understand why an accidental discharge is possible.

In reality the essential limbs of a lock work on the principle of a cog-wheel and ratchet, as may be seen in Fig. 5. It should be clearly understood that these diagrams are not intended to represent any particular type of lock, but merely the principle on which all locks function.

The two essential limbs consist of a wheel, or "Tumbler," A, which is fixed to an axle, B, which in turn rotates in two bearings in the lock. This wheel is actuated by a spring, termed the "Main Spring" (not shown for the sake of simplicity) which is compressed when the lock is cocked and then tends to rotate the tumbler and axle in the direction of the arrow. There is a cog, or "Bent," C, in the lower edge of the tumbler; and in this bent there fits a ratchet, or "Sear," D, which pivots about a peg, E. The front end of the sear which actually fits in the bent just as a ratchet does in a cog, is termed the "Nose," while the other end of the sear is called the "Tail." The sear is also actuated by a spring, known as the "Sear Spring," which depresses the tail and so tends

Arrow Tumbler LockForensic Ballistics

Fic. 5.—Diagrams to illustrate the principle on which a shotgun lock works.

A, Tumbler. B, Tumbler axle. C, Bent. D, Scar. E, Sear peg. (<j) Cocked position. (b) Fired position.

to keep the nose in the bent, as shown in Fig. 5 (a), which indicates the tumbler and sear when the lock is at full cock.

The trigger is merely a lever which is situated under the sear tail, and when the trigger is pressed it lifts up the sear tail, thus dropping the sear nose downwards out of the bent. When this happens the tumbler is no longer held in position; the main spring asserts itself and rotates it, together with the tumbler axle, with force and rapidity until the limbs are in the positions shown in Fig. 5 (b)y where the sear tail has been lifted by the trigger.

The hammer is fixed to the tumbler axle, and so rotates with it. This rotation is termed the "fall" and is usually through an angle of about 30 degrees. At the end of its fall the hammer strikes the firing-pin, or striker, which in its turn hits the cap, and so causes discharge.

When the lock is cocked the hammer is pulled back, thus rotating the tumbler axle and tumbler in the reverse direction against the main spring, and when the rotation is complete the sear nose slips into the bent owing to the pressure of the sear spring on the sear tail. In fact, the lock is then "wound up" again.

All locks work on this general principle, although in bolt-action weapons the tumbler is replaced by a unit which slides backwards and forwards instead of one which rotates. But the principle of the bent and sear remains the same.

Plate XI (¿1) shows the right lock of an ordinary hammer gun in the full-cock position. A portion of the plate which carries the lock mechanism (termed the "Lock Plate" or "Side Plate") has been cut away as has a bit of the wood of the stock into which the lock plate fits. This has been done to show the sear nose in position in the bent.

Now it will be realised that there are two forces tending to keep the sear nose in the bent: the pressure of the sear spring on the sear tail, and the pressure of the bent against the sear nose which is due to the main spring.

Of these two forces the former is comparatively feeble, and the latter depends on the way the sear nose fits into the bent. That is on: the depth of the bent; the shape of the bent; whether the sear nose fits right home in the bent or not; and the relative positions of the centre of the tumbler axle, the sear nose and bent in the full-cock position, and the sear peg.

All these points need attention when considering whether any particular weapon is abnormally liable to accidental discharge, but it can generally be assumed that in a gun of proper construction the easier it is to pull the trigger and fire the gun the more liable that gun is to accidental discharge.

For if the trigger pull is very light it must mean that the forces holding the sear nose in the bent are not very strong, in which case a sudden knock or blow will easily jar the sear out of position, and the gun will be discharged. And this is one of the reasons why a very light trigger pull is commonly, and quite rightly, considered dangerous.

Hammerless guns are fitted with a safety slide, and there is a widely held belief amongst sportsmen that the operation of this slide actually cocks and uncocks the locks. In reality it does nothing of the sort, but merely bolts the triggers and so prevents them from being pressed against the sear tails. A safety device is unquestionably an extra element of safety, but when a gun is at "safe" it is still quite possible for it to be jarred off, although it is not so fully prone to accidental discharge as it is when the slide is not at "safe."

This liability to accidental discharge was recognised in the early days of hammerless guns and resulted in the invention of various "automatic intercepting safety" devices. I will not enter into any details of such mechanisms here, merely indicating that their object is to prevent the tumbler rotating unless the trigger has been actually pressed. In theory these intercepting safeties are perfect, but in practice it is to be feared that they are not. At the same time they undoubtedly do provide an extra element

Accidental DischargeForensic Ballistics

(À) TWO DIFFERENT -303 CARTRIDGES Both fired by the same rifle


Both fired by one rifle, but a different rifle from that used to fire the cartridges shown in A


Both fired by the same nfle, but a different rifle to either used to fire the cartridges shown in A and B

of safety, and on this account they are almost invariably fitted to all good-quality hammerless guns and rifles.

Hammer guns are seldom now fitted with the special safety stops which used to be seen on double hammer big game rifles and which certainly did lock the hammers when in the full-cock position with great efficiency. Consequently a hammer gun at full cock is less safe than a hammerless gun from the point of view of accidental discharge.

Similarly all rifles, pistols and revolvers are liable to accidental discharge when at full cock. Many of these weapons are fitted with safety devices which vary in degrees of efficiency, some being undoubtedly so effective as to render the weapon as safe as any loaded weapon can ever be.

But if the safety device is not in action pistols and revolvers are just as liable to accidental discharge when at full cock as any other type of weapon.

It can, in fact, be assumed that in actual practice no weapon can be regarded as immune from the possibility of accidental discharge if it can conveniently be fired by pressing the trigger in the normal way.

This should never be forgotten, and if any accident or fatality occurs owing to an alleged accidental discharge and suspicion falls on any individual the weapon in the case should be examined carefully and thoroughly in order to make sure that it is in good order, as any maladjustment of a lock mechanism can easily render a weapon peculiarly liable to accidental discharge.

And in this connection it may be of interest if I give some brief details of an actual case, especially as there can be no better instruction than a study of different methods of investigation.

A smallholder and his grown-up son were working together in the yard of their farm. The smallholder had a borrowed gun with him which he loaded, cocked and leant against the wall of one of the buildings so as to be ready in case any geese came over, as they frequendy did at that time of year. Of course such carelessness is unpardonable, but it is unfortunately all too common.

The smallholder's story, which he told immediately to two neighbours to whom he ran for help and which he never once changed in any single detail, was that his son was shovelling some refuse within a few feet of where the gun was standing while he himself went to let their dog, a big heavy retriever, out of its shed. He did this and the dog rushed round the yard in excitement, and knocked the gun over. The gun was discharged and the son was shot.

After some delay the smallholder was arrested for murder, the case for the prosecution being that the gun was in perfect condition and could not possibly have been discharged accidentally, while the direction of the wound was such that the gun must have been in someone else's hand when fired.

No sort of evidence of motive was forthcoming, and the nearest approach to any serious quarrel had occurred four years before.

Now one of the commonest tasks which gunmakers are asked to perform by their customers is to overhaul their guns. Many shooters send their guns to their gun-makers at the end of every season for a periodic overhaul, and the gunmaker naturally removes the locks and, generally takes the action to pieces in order to see whether every part is in proper condition and free from rust, and whether all screws are tight, and so on. This is normal business routine, as it is utterly impossible to form any opinion as to the condition of the internal mechanism without examining it.

It is also by no means a rare occurrence for some shooter to ask his gunmaker whether his gun is in its normal safe condition or whether it has in any way become abnormally prone to accidental discharge. In such circumstance the gunmaker must take off the locks of the gun, as it would be impossible for him to form any useful opinion without examining their mechanism.

At the first day's hearing before the magistrates, however, cross-examination elicited the fact that the Prosecution had formed their opinion that the gun was "in perfect condition" and could not be discharged accidentally, without ever having taken the locks off to examine them, and had apparently arrived at their conclusion by testing the weights of the trigger pulls. That of the right trigger was exceedingly heavy, so heavy in fact that this lock probably was immune from accidental discharge.

But it was the left barrel which had been fired, and the trigger pull of the left lock was much less, being 7 lb., winch is certainly heavier than that of a good-quality gun, but not particularly heavy for the left trigger of a cheap gun, since the pull of the left trigger is usually heavier than that of the right so as to reduce the possibility of the left lock being fired accidentally at the same time as the right.

Further cross-examination brought to light the fact that these trigger pulls had not been measured with a dead weight, which, as will be seen later, is the only possible method of obtaining an accurate result, but with a spring balance.

It was at this point in the proceedings that I was asked by the defending solicitor to examine the gun with a view to giving an opinion on its safety.

From an inspection of the outside of the gun I noticed two conditions of the left lock which suggested something being radically wrong.

In any lock which is in proper condition there should be a slight, but perfectly distinct, feeling of play on the trigger when the lock is at full cock. This is purposely left by the gunmaker in order to allow for the possibility of any change in the wood of the stock due to swelling or shrinkage caused by damp or dryness, and is thus a very important safety factor. In the left lock of the gun in question, which was a very inferior-quality gun, having all the signs of the cheapest type of continental manufacture, the trigger was absolutely rigid when the lock was cocked. This must always be a dangerous state for any trigger to be in, as there is no "give" in the case of a fall or knock, and so the force of such a fall is transmitted direct to the sear and the risk of accidental discharge is much increased.

The second point was that when the left lock was in the "down," or what is commonly, but not accurately, called the "half-cock" position, the hammer could be pushed right forward against the striker and the gun could be fired.

In my brief description of the mechanism of a lock I purposely confined myself to the principles which govern the actual firing of a lock. Hammer guns, however, have an additional cog, or bent, in their tumblers into which the sear nose fits when the hammer is not at full cock. In early guns this position was known as the "half-cock" position, and constituted the safety device, as when a lock was at true half cock the gun was immune from accidental discharge (owing to the deepness and shape of the bent) while the hammer could not possibly be pushed forwards against the striker.

In modern hammer guns the hammer automatically

Shotgun Accidental Discharge

Six -455 Revolver Cartridges all fired by different Service Revolvers made in the same factory rebounds back into this position after firing, and so the safety dcvicc is automatic. The safety bent in the tumbler is called the "rebound bent/'

In cheap guns there is often slight play of the hammer in the rebound position because the sear nose does not fit quite snugly into the bent, and when this occurs the hammer can be pushed forwards towards the striker to a limited degree which varies with the amount of play between sear nose and bent. But the forward movement of the hammer is always limited, and not complete.

In the left lock of the gun in question there was no sort of limit to this forward movement of the hammer, although there was such a limit in the right lock. This fact also indicated that there was something radically wrong with the left lock.

Accordingly I took the locks off, which was only the work of seconds rather than minutes since it was merely necessary to remove two screws in order to lift the locks off the stock.

The cause of the trouble in the left lock was then immediately obvious. The limbs had not been properly adjusted and the tail of the sear protruded below the edge of the plate which carries the whole lock mechanism. Now the wood of the stock is recessed to accommodate this mechanism and the lock plate fits exactly into the mouth of this recess so as to render the gun weatherproof.

It will be perfectly obvious that if any part of the mechanism protrudes beyond the edge of the lock plate, either that part must be forced out of position when the lock is in position on the gun, or else the lock plate will not completely cover the mouth of the recess.

In this particular gun the sear tail of the left lock had to be lifted up by about ¿V of an inch in order to permit the lock being fitted into its recess in the stock, and the result was that the sear tail was pressing hard on the wood of the stock all the time. The effects of this pressure on the wood were threefold—

(1) The sear nose was lowered and so could not engage fully in the bent when the lock was in the full-cock position.

(2) Similarly the sear nose could not engage at all with the rebound, or safety, bent, and this explained why the hammer could be pushed right forwards without any sort of check when the lock was at "half cock."

(3) The fact that the sear tail was pressing hard on the wood of the stock meant that any blow on the stock would be transmitted direct to the sear tail.

The combination of the first and third of these effects obviously rendered the gun peculiarly dangerous and liable to accidental discharge.

The effects of this lifting up of the sear tail by the pressure of the wood can be seen in Plates XI and XII. Plate XI (6) shows the left lock of the same gun as that shown in Plate XI (a), but in this case the sear tail has purposely been bent until it protruded beyond the edge of the lock plate. The effect of the tail being lifted by the wood when the lock is at full cock is clearly seen, as part of the lock plate and wood have again been cut away to show the sear nose and bent. A comparison of the two photographs will show that while the sear nose is right home in the bent in Plate XI (<2), it is only half into the bent in Plate XI (b). And in this position it will clearly be much more easily knocked right out of the bent by a sudden blow.

Plate XII shows the effect when the lock is at "half cock." Here again the right lock (Plate XII (d)) is as it should be, and the sear nose is engaging with the rebound bent, while in the left lock (Plate XI (b)) the nose has xxr

Forensic Ballistic Investigation
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