– how bump stocks work

Question

I understand what bump stocks do from reading up on them, but I haven’t found an explanation of how they work. They allow firing a semi-automatic weapon more quickly by using recoil to move the rifle back and forth (“bumping”) against the trigger finger. What I don’t understand is what is different in a bump stock compared to a regular stock. In my mind, I envision a big cartoonish spring in the bump stock that moves the rifle back forward after the initial kick from recoil. How does it work exactly?

In: Physics

Answer 1

So bump firing is a technique to get a semiautomatic firearm to fire repeatedly. It works because the receiver, stock, grips, and your arms/shoulder all act as a spring-mass-damper system together. When you fire the weapon, it recoils back into your grip, and then shifts forward again as your grip/shoulder pushes the gun back forwards. If you adjust your stance a bit, or use stiffer objects than your finger over the trigger (e.g. a stick), you can ensure that each time the weapon cycles and begins to shift forwards, the trigger will get pulled again and keep firing as fast as the weapon can cycle.

You can hypothetically do it with any semi-automatic weapon, with no modifications, but realistically it’s only ever something you can do on rifles, and it’s typically a sign that the trigger mechanism was installed poorly or is going bad. It’s also something that can be done deliberately with no real effort (e.g. using the belt loop on your jeans to stiffen your trigger finger, using a stick off the ground, etc.).

You can also modify the weapon to make bump firing more easily achievable, typically by just adjusting the trigger mechanism or by modifying the stock to change how stiff it is. However, you can take it a step further and use a bump stock.

A stereotypical bump stock also allows the receiver to move back and forth into the stock (against a spring), which also makes bump firing easier.

“True” bump stocks could hypothetically be regulated because they tend to all work the same way, kinda, and because they essentially have no purpose other than making bump firing easier (because the bump stock is a really really shitty stock, by design), but bump firing itself would be impossible to regulate.