General Theory About Recoil Operated Firearms 

Abstract:

              Recoil operated weapons depend on the recoil force to open the bolt and related parts. The bolt is locked during firing by the spring pressure, after firing the bolt is unlocked automatically by the recoil force of the firearm after the chamber pressure is dropped to safe level. Normally it has classified in two categories they are: 

• Long recoil 

• Short recoil 

Let see the terms one by one,

 1.Long recoil:

               In the long recoil the bolt and barrel both are act as a unit and travels the entire distance, the recoil distance is greater than the length of the complete round because to load a new round. At end of the recoil stroke the bolt is held and barrel counter recoils alone, when the enough space is developed between the bolt and the barrel the bolt will eject spent case and reload a new cartridge. 

For example: Chauchat Light Machine gun 

2. Short recoil: 

             In the short recoil the bolt and barrel both are act as a unit and travels distance shorter than the complete round. The bolt is unlocked before the barrel complete its full stroke. The bolt travels rearward by the help of the momentum acting on the bolt. When the enough space is developed between the bolt and barrel, in that time the extraction and ejection occur and the new cartridge is chambered.

 For example: MG 34 and M2 browning 

❖ Note: In recoil operated weapons mostly the barrel is loaded with spring.

 • Dynamics Of Long Recoil: 

              The dynamics of the long recoil firearms are similar to blowback operated weapons, in blowback weapons the barrel is fixed but other parts are movable. Here the barrel and bolt is movable and both are act as a same unit and travel a distance with the time of recoil. The time of recoil may be reduced due to the delaying action of the recoil absorption at the end of the recoil stroke, the above action can be done by using a heavy buffer spring. Mostly the recoil operated weapons barrels are loaded with spring, the spring should be stiff enough to hold the barrel and recoiling parts in battery whereas the bolt retuning spring is capable to close the bolt in minimal time. A stiffer spring (higher spring constant) will generally take less time to return, and the firing rate can be depended up on the spring stiffness. The driving spring should have the properties to absorb the recoil the energy of the bolt, when fully compressed the buffer spring approximately equals that of the barrel spring, this arrangement gives the barrel sufficient momentum at the beginning of the counter recoil stroke for a quick return without inducing excessive impact when 3 stopping the retuning barrel. The springs are used in the barrel of the long recoil weapon for retuning the barrel to its initial position after the recoil kick of barrel before completing of the counter recoil of the bolt and buffer spring. In long recoiled weapons the kickback of the barrel and bolt both are act as same unit and travels the rearward distance is known as recoil.  Refer figure 1

Counter recoil refers to the process of returning the parts of a firearm, such as the barrel and slide or bolt, to their original forward position after they have moved backward due to the recoil force generated by firing a round.

• Dynamics Of Short Recoil: 

              The dynamics of the short recoil weapons is similar to retarded blowback (delayed blowback) more nearly than the long recoil. To eliminate the blowback tendencies here the bolt is not unlocked until the pressure drops at safe level. In the time of battery the bolt is locked with the barrel extension and it act as a same unit, after firing a round the barrel kick back the bolt due to the force generated by the recoil, the bolt and barrel unit travels a shorter distance after that both are disengaged and barrel goes to its original position by the force generated by the barrel spring, the barrel travels lesser distance than the bolt and the barrel will stop the recoiling before the bolt. The bolt continues its rearward motion due to the momentum acting on the bolt, in this time the enough space created between the bolt and barrel for completing the extraction, ejection, and chambering the new round.  Refer figure 2

• Muzzle Boosters 

                Generally, the recoil operations are used in general purpose machine guns and heavy machine guns and cannons. The muzzle boosters are the device that is attached in the muzzle of the recoil operated firearms, these devices are totally differ from the flash hiders and muzzle brakes. The main purpose of the muzzle boosters is to increase the fire rate of the weapon. The muzzle boosters include flash arrester and a booster cone and the barrel sleeve muzzle booster is threaded with the barrel jacket of the recoil operated firearms such as MG 34/42.  Refer figure 3

        a) Flash arrester: It is a component in the muzzle booster that holds the booster cone assembly                                             also it acts as a flash arrester to arrest the flash during firing.  Refer figure 3

        b) Booster cone: It is a cone shaped cup that traps the high-pressure gas, smaller diameter exists                                         hole trap more pressure and give higher fire rate. Refer figure 4

         c) Barrel sleeve: It is a cylindrical sleeve to hold the barrel in position. Longer sleeve traps more                                        pressure also the deeper V cuts trap more pressure.                                                                                      Refer figure 5 

          

          d) How the Muzzle booster works:

            After firing a round, when the round leaves the muzzle of the barrel and it go through the booster cone, in this time some of the hot gasses are trapped by the booster cone. So, the trapped gas inside the cone creates back pressure and it kicks the muzzle of the barrel in rearward direction, depending upon the back pressure developed by the trapped gas will increase the recoiling, once the recoiling will increase means the firing rate will be increased. In simulation without booster the MG 42, gun fires 900 rounds per minute, with booster it fires 1200 rounds per minute. Mostly in germen recoil operated weapons barrel fore end look like a piston also the rings are in the barrel fore end such as MG 34/42.

Figure 1 schematic of long recoil system

Figure 2 schematic of long recoil system

Figure 3 schematic of muzzle booster of MG 42

figure 4 schematic of booster cone

figure 5 schematic of barrel sleeve