Basically, all locks work on the same principle: a spring-loaded rotating (as in a weapon with a hammer) or sliding (as in a bolt action weapon) hammer with a small notch cut in it called a ' bent'. Into this bent fits one end of a pivoting lever which is called the ' sear'. The other end of this lever either forms or is actuated by the trigger. When the lock mechanism is cocked, the sear contacts the bent and holds the hammer or striker in the cocked position until the trigger is pulled.
The contact between the bent and sear must be minimal; otherwise, the pressure required to disengage the two would be excessive. Likewise, the contact surfaces must be parallel to ensure a smooth disconnection. A hooked bent would be all but impossible to disengage, whilst a rounded surface could slip out of contact under the spring tension of the lock.
Most accidental discharges caused by faulty lock mechanisms can be attributed to a bent/sear fault. Illustrative cases would be appropriate to exemplify this aspect of accidental discharge.
Case example: Faulty lock mechanism. An alleged case of accidental discharge involved a husband/wife dispute where it was claimed the gun went off accidentally whilst unloading the weapon in the front room. The wife was shot in the head, killing her instantly.
The weapon involved was an extremely expensive Italian side-by-side doublebarrelled 12-bore shotgun which had only been used twice before. Trigger pull testing showed that the right and left trigger required a pressure of 4 and 4ylb , respectively, which is considered acceptable for a weapon of this type.
Tests for accidental discharge consisted of blows with a soft mallet to the heel of the butt, the top and bottom of the lock mechanism, and the muzzle end of the barrel. These tests showed that there was no tendency to accidentally discharge, though jarring was found.
During test firing, it was noted that with each successive pull of the trigger, the pressure required decreased significantly.
Further tests to determine what actual pressure was required on the trigger to fire the weapon showed that it had, after just a few test firings, fallen to less than 2 lb. It was also found to be very prone to accidental discharge by jarring. After just two additional trigger pull tests and two accidental discharge tests, the trigger pull had dropped to less than 1 lb and then to the point of not being able to cock the mechanism at all.
On disassembling the lock mechanism, it was found that the steel bents of the lock mechanism had not been case hardened during manufacture. On each pull of the trigger, the much harder sear had stripped metal away from the bent until it no longer existed.
Although the weapon was in good working order and not at all prone to accidental discharge when received, there were doubts as to the changing characteristics of the weapon's lock mechanism, and the case was dismissed.
Case example: Gun damage through poor exhibit handling. Another case involved the shooting of a man by a gypsy armed with a 0.410" shotgun. As usual, it was claimed that the gun had gone off accidentally whilst trying to fend off the allegedly aggressive man and that there was no intention to kill him.
The weapon concerned was a cheap quality, single-shot, bolt action weapon of continental manufacture. It had an excessively high trigger pressure of 12 lb, and there was absolutely no tendency for it to accidentally discharge.
During the trial, the prosecution requested a demonstration as to the method used to test for accidental discharge. The weapon was cocked and as the gun was turned round to strike the heel of the weapon on the floor, it lightly brushed the top of the witness box. There was a very audible click as the firing pin fell which at that point sounded like thunder. At that stage, prosecution asked for a recess.
On disassembling the weapon, it was found that the action had been driven back into the woodwork of the stock to such an extent that the sear was being pushed out of contact with the bent. In addition, the heel of the stock was found to be battered and cracked where it had been repeatedly hammered on to the floor.
Obviously, nobody was going to accept responsibility for this damage, but it was suspected that everybody involved in the case had to convince themselves that the weapon was not prone to accidental discharge.
After the recession, I informed the jury that when I received the weapon, it was in good working order and not at all prone to accidental discharge. I also explained that at some point after the weapon left my control, it had been dropped on its butt, probably many times, and damaged to the point where it was not at all in the condition as first received. The prosecution counsel did not object to this explanation and the case was allowed to continue on the evidence as to what the condition of the weapon was in when originally received by me.
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