Momentum plays a large role in how much force is imparted to the target, and how much recoil the user of the firearm experiences.

MV+mv=0

    The equation above depicts the law of conservation of momentum being applied. The law of conservation of momentum states that the total amount of momentum that is in the system must be conserved. In the above scenario the Mass of the gun and the person combined is M, and the velocity of that system after firing the bullet is V, while the mass of the bullet is m, and it velocity is v.
    Analytically the mass of the bullet compared the rest of the system is extremely small. We can imagine when the bullet is fired, the velocity of the person and the gun is very nearly 0, therefore the velocity of the bullet must be extremely large for the conservation of momentum to stay true.