Posted on May 18 2020
Newton's First Law states that an object at rest will remain at rest unless acted upon by an outside force. An object in motion continues with the same speed and direction unless acted upon by an external force. This law is "the law of inertia." More simply, this means that the gun is not going to move by itself or counter-recoil by itself. The firearm will not move or exert a force until a force is upon it. This is easy to envision, and also applies to pistols as well. The recoil process is determined by the(recoil force).
The counter-recoil force is generally applied over a long period and adds forward momentum to the gun equal to the backward energy supplied by the recoil force, to bring the gun to a halt. There are two special cases of counter-recoil power: Free-recoil, in which the time duration of the counter-recoil force is much larger than the duration of the recoil force zero-recoil, in which the counter-recoil force matches the recoil force in magnitude and duration. Except for the case of zero-recoil, the counter-recoil force is smaller than the recoil force but lasts for a longer time. Since the recoil force and the counter-recoil force are not matched, the gun will move rearward, slowing down until it comes to rest. In the zero-recoil case, the two forces are matched, and the firearm will not move when fired.
In most cases, a gun is very close to a free-recoil condition, since the recoil process generally lasts much longer than the time needed to move the ejecta down the barrel. An example of near zero-recoil would be a gun securely clamped to a massive or well-anchored table, or supported from behind by an enormous wall. However, employing zero-recoil systems is often neither practical nor safe for the structure of the gun, as the recoil momentum must be absorbed directly through the minimal distance of elastic deformation of the materials the arm and mount are made from, perhaps exceeding their strength limits. For example, placing the butt of a large caliber gun directly against a wall and pulling the trigger risks cracking both the gun stock and the wall's surface.