Understanding Recoil

RECOIL STAGE ONE.... To quantify recoil, there are 4 separate items that must be considered as part of a system; the rifle, bullet, powder, and the shooter's shoulder mass. Just before the firing pin strikes the primer, the CG (Center of Gravity) of this "system" is somewhere around the middle of the action. The principal of conservation of momentum requires that unless an outside force acts upon a system, the system's CG must remain at the same location. The firing pin hits the primer, the powder burns and the bullet travels to the end of the barrel. The base of the bullet is just ready to exit the barrel. Stop time and look at the condition of the system. The CG of the powder mass has moved forward and is near mid barrel, the CG of the bullet is just outside the end of the barrel. Since the CG of the total system must remain in its original location, the rifle and shooters shoulder must move aft to preserve this original CG position. Also, since the hot gas and the bullet have a forward velocity, the conservation of momentum requires that the rifle and the shooters shoulder have a proportional velocity aft.

The speed at which this process occurs is the difference between a gentle push and a sharp jolt. A high velocity, heavy bullet, and heavy powder charge reacting in a very short interval of time all contribute to increase the severity of the recoil at this point. But this is only part of the rifle's recoil, since this is still a closed system.

The recoil of stage one can only be reduced by:
1. Decreasing the bullet mass
2. Decreasing the bullet velocity
3. Decreasing the mass of the powder
4. Increasing the mass of the rifle
5. Decoupling the shoulder mass from the system by putting some intermediate shock absorbing material between the rifle and the shoulder.
6. Using the unique muzzle brake below (that operates before the bullet has exited the barrel).

RECOIL STAGE TWO.... Now advance time, the rifle has a velocity aft, the bullet leaves at its velocity and the system is no longer a closed system. The bullet can no longer affect recoil and has done all it will do in creating recoil. But the barrel is full of hot high pressure gas. There is a reaction imparted to the rifle system as the compressed gas column forces gas out of the end of the barrel at very high velocities (most of it exiting at a much higher velocity than that of the bullet). It is a miniature rocket engine accelerating the rifle aft. The rifle already with a velocity in the aft direction from stage one gains even more velocity and there is a significant increase in recoil. The energy in the hot compressed powder gas can be harnessed to reduce recoil by using a muzzle brake.

STANDARD MUZZLE BRAKE.... The energy still remaining in this compressed gas column at the start of stage two is what makes a muzzle brake reduce recoil. Since the gas is expanding, only a small amount of the expanding gas exits through the bullet hole of the muzzle brake. Most of the gas hits the port surfaces of the muzzle brake and is deflected to the side (stops the forward velocity, good) or is deflected aft (accelerated in the aft direction, best) and forces the barrel forward. This forward directed force reduces the rearward velocity the rifle had just before the bullet left the end of the barrel, in stage one. With a muzzle brake, a larger powder charge is more effective in reducing recoil because there is more mass available to force the rifle forward.

INTERESTING MUZZLE BRAKE.... Here is an interesting concept in a muzzle brake that reduces the sound as well as the recoil. This design would do a very good job, because, it uses almost all of the powder gas to reduce recoil before the bullet even leaves the end of the barrel in stage one. But it is complicated to build and a bitch to clean. Click here to view the design. The WayBack Machine has saved the site. The design was essentially a thin tube that enclosed the barrel. The gas ports about 2 inch from the end of the barrel and inside the tube, allowed gas to be captured in the annulus and then to slowly escape back through the ports out the end of the barrel bore after the bullet had left.

Posted here with permission from the Author, " Varmint Al "