Safety Mechanisms: Drop Safety

In our last post, we studied a Glock pistol for its integrated trigger safety, but we also noted that the Glock feature two additional safeties, that guard against discharge if the firearm is accidentally dropped. We will study more about those mechanisms in this post.

Mechanisms that prevent the firearm from going off when dropped or roughly handled, fall under the class of Drop Safety. These safeties work by providing an obstruction between the firing mechanism and the cartridge and are connected to the trigger. As the trigger is being pulled, these safety devices are deactivated one after other with the trigger movement. Therefore, if the firearm is accidentally dropped, the drop safety devices are all active since no one is pulling the trigger. Hopefully they work and therefore stop the firearm from going off accidentally.

The first drop safety we will study is something we mentioned in the previous article, a firing pin block safety. This is a mechanism that sits in the path between the firing pin and the cartridge primer and prevents the firing pin from striking the cartridge, when it is active. The firing pin block is connected to the trigger and as the trigger is pulled back, the firing pin block moves out the path between the firing pin and cartridge, just before the hammer is released. The hammer then strikes the back of the firing pin and the front of the firing pin can now freely strike the base of the cartridge, since the firing pin block is now out of the way. When the trigger is released, the firing pin block moves back into place again and blocks the firing pin from striking the cartridge.

The next drop safety mechanism we will study is the hammer block. The concept is very similar to the firing pin block, except that in the case of the hammer block, the mechanism sits in between the hammer and the back of the firing pin. So when it is active, the hammer cannot strike the back of the firing pin. Like the firing pin block safety, this mechanism is also connected to the trigger and the hammer block moves out of the way as the trigger is pulled.

The next drop safety mechanism we will study is the transfer bar, which is used in revolvers. In this case, the hammer does not directly strike the cartridge. Instead, there is a transfer bar that has a firing pin attached on the other end, which contacts the cartridge. When the firearm is not in use, the transfer bar is moved out of the way between the hammer and the cartridge (which is the opposite of the other mechanisms we have seen so far.). So if the firearm is dropped accidentally and the hammer releases due to impact, the hammer still won't contact the cartridge When the trigger is pulled, the transfer bar is moved into position just before the hammer is released. The hammer now strikes the transfer bar and the other end of the transfer bar which is connected to the firing pin then strikes the cartridge and discharges the firearm.

The last drop safety mechanism we will study is the oldest one: the safety notch. Unlike all the others that we've studied so far, this is a feature that needs to be engaged by the user manually. This type is used by old revolvers, lever action rifles, some old semi-automatic pistols etc. The safety notch is a cut made to the tumbler and connected to the hammer. If it is engaged, the hammer is caught before it can strike the firing pin. Therefore, if the weapon was fully cocked and if the safety was turned on, even if an accidental drop releases the hammer, it is caught at a half-cocked point by the safety mechanism.

In many areas, the law now requires that all new firearms have at least one form of  drop safety on them. Many pistols have more than one drop safety mechanism, so that if one of them is worn out, one of the others will hopefully work and prevent the pistol from accidentally discharging.