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On handling the problem of automation in automatic weapons (AW), it is important to analyze the motion of these weapon mechanisms during their function cycle [1, 2]. Many activities are performed during the backward motion of weapon mechanisms using the power of branching gases from what known as Gas Unit (GU). These activities starts with under-slide motion, unlocking, extraction of empty Cartridge Case (c.c.), backward motion against springs, ejection of empty c.c., and ending by loading of trigger at the extreme rear position. All these activities are performed in a reversed manner during the counter recoil track. In this paper; the parameters affecting the momentum of branching gases have been extensively studied, the performance of the gas unit is converted to touchable figures in order to facilitate the evaluation. These evaluations are presented in forms of change in pressure of gases inside the GU, maximum velocity of recoil, and the displacement of recoiling parts until the pressure inside the gas unit reaches the atmospheric value [7,8]. The predicted results determine the weight of each parameter that affects the momentum of gases. Moreover, the affecting parameters of GU on the weapon performance during the function cycle may be considered on modifying the power of in-service weapons, or the newly designed generations * Egyptian armed forces. 33 BL Proceedings of the 15 Int. AMME Conference, 29-31 May, 2012 HISTORICAL PREVIEW ON REGULATION OF GASES IN FIREARMS Before the Russian scientist Michael Kalashnikov had started his work designing and producing his worldwide famous design of the Automatic rifle AK47, other investigators have been worked hardly in order to reach the different ways of automation [12, 3, 4]. In the following; samples of the worldwide patents in the field of gas regulation are introduced. These patents are concerned with the optimization of the use of produced gases from burning of propellant charge in driving the mechanisms of the firearms automatically. In 1929; Frederick studied the arrangement developed by Browning (Feb. 1919) in his automatic weapon GU model; and he decided to simplify his constructional arrangement offering new features [2] simply characterized by: iSupplying a piston with three sealing stations as marked by the numbers 17,18 & 19 in Fig.1. iiInserting a regulating plug with three different sized orifices that allow setting of gas regulator in 3 positions. These positions are presented on Fig.1 by marks 12-a, 12-b, and 12-c each opening has different cross Fig.1. Frederick idea of GU regulator. sectional area of gas vent, these vents control the rate of fire or they may be adjusted in three stages having the life time of the automatic firearm. In Fig. 2 of a gas regulator is simply the patent introduced by John Garand 1945; it allows a wide control over the initial volume of gas unit chamber. It allows the possibility of suppressing the effect of sudden increase in gases; especially when using different types of ammunitions in the same firearm. Such design considers the release of excessive flow of gases in a way similar to the function of relieve valves [3]. In 1949, Moore [4] introduced a new idea, this invention is related to the improvements in an automatic firearm, wherein the firing mechanism was operated by means of branching gases which are allowed to escape from the barrel (7) and acted upon a movable piston (5) and is directed impinging on the piston which in turn is regulated. The control of these produced gases in such a fire-arm was very desirable not only to allow for the fluctuation of the pressures of the escaping gases but also to eliminate in so far as possible the excessive effect of their sudden increase. 34 BL Proceedings of the 15 Int. AMME Conference, 29-31 May, 2012 Fig. 2. Garand construction of gas unit regulator [3]. Fig.3. Moore construction of gas unit regulator [4]. Moore has introduced a complicated structure for gas unit regulators, in which gases branches from barrel bore through orifice at (part 7) after which regulation took place in a cylindrical perforated structure (part 56) which was fed by gases from a cavity (part26), and the main opening (part60) leading to 3 different gas vents. 35 BL Proceedings of the 15 Int. AMME Conference, 29-31 May, 2012 REGULATION OF INTENSITY OF POWDER GASES IN THE CHAMBER Rather than other arrangements in automatic weapons with gas operated systems allow the wide control over the power of fire in AW through: changing the position of gas vent with respect to barrel bore, selecting the optimum values of the mass of recoiling parts, and finally enhancing the effect of heat transfer to minimize the loss of gas energy branching through the gas vent. On other hand, the effect of the control parameters depending on the geometrical characteristics of the gas unit cannot be ignored. These parameters are: area of gas vent, changing the initial volume of gas chamber, and controlling the outlet of gases from the gas chamber [7]. Factors Affecting the Performance of Gas Unit The parameters affecting the performance of gas unit can be studied based on the following factors; which are divided into two groups as: (i) Group A: The parameters affecting the efficiency of Gas unit are: a Minimum diameter of gas vent; (do) b Initial volume of gas chamber; (Wo) c Diametric clearance between piston and the cylinder; (∆Sp) d Area of piston head; (Sp) (ii) Group B: The parameters affecting the momentum of gases are: a -Position of gas vent with respect to the barrel bore b -Mass of moving parts; (MRP) c Conditions of heat transfer According to the work of Prof. Dr. Mamontove [7, 8], he introduced an analytical relations that correlates the change of gas pressure inside the gas cylinder with time. k km z km z p p e p e z e z = = − − . . . . . 1 (1) where Pk is the pressure of gases inside the gas chamber, Pkm is the maximum pressure inside the gas chamber, z is the dimensionless time ratio m t t z / = , t is the time variable inside gas unit, and tm is the time duration till the pressure reaches its maximum value in gas unit. k km m t tm p p e t e t = −− . . . (2) Knowing the pressure time relation inside the gas unit, Pk(t), it is possible to determine the important parameters (Pkm, tm , tk), where tk is the time corresponding to the end of action of gases. Figure 4 shows the pressure variation against the relative time of gases expansion inside and outside the barrel, while the branching gases diagram Pk(t) shows the moment and position before which the gas unit opening should not be located. 36 BL Proceedings of the 15 Int. AMME Conference, 29-31 May, 2012 Fig. 4. Schematics diagram of gas pressure-time in barrel bore and gas unit. As will be discussed later; knowing any two parameters is sufficient to determine the other missing parameters. In the following, a set of functions have been listed forming a set of empirical formulae which help in solution of the above task inside the gas chamber. In addition, these empirical formulae are used for determining all required motion parameters. GASES PRESSURES VARIATION INSIDE THE GAS UNIT (Pk(t)) Applying Eqn. (1), the pressure variation inside the gas unit is represented by:

ANALYTICAL STUDY OF GAS UNIT GEOMETRICAL CHARACTERISTICS AND THEIR IMPACT ON THE MOMENTUM OF RECOLILING PARTS