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Figure 2-29. Effect of Barrel Return Spring on Barrel Motion After Acceleration.

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loss due to the effect of the spring constant is determined by the method of step 4 of the procedure previously dcscribcd and the modified curves are designated as step 5. Since the performance of step 6 produces a negligible changc in the curvcs, the curves drawn in accordance with step 5 represent the eilect of the barrel spring on the barrel motion. The curvcs show that if the barrel spring alone resists the barrel motion after the acceleration action is completed, the barrel will move an additional 0.033 foot (0.40 inch) and will come to a stop at 0.0193 second. Both this distance and the time are a little too great since it is desirable to stop the barrel as soon as possible. Therefore, a stop will be provided to limit the barrel movement to 0.250 inch (0.0208 foot) after acceleration is completed. As indicated in fig. 2-29, this movement occurs at 0.132 second. At this point the velocity of the barrel is only 3.70 feet per second and therefore has a kinetic energy of only 9.55 foot pounds, indicating that the shock of hitting the stop will be relatively light. After being halted by the stop, the barrel is latched in place so that it remains in its rearmost position. This is shown in fig. 2-29

bv the fact that the barrel travel curve is a horizontal line after 0.132 second. The data from fig. 2-29 are used to extend the barrel motion curves on the graph (fig. 2-30) showing the motion curvcs for the complete cycle.

### 7. Bolt recoil motion after acceleration

At the end of the acceleration period, the bolt is moving with a velocity of 60 feet per second and its motion from this point on is resisted only by the bolt driving spring. As shown on fig. 2 30, the barrel is latched at a displacement of 0.156 foot (1.875 inches). Since it has been assumed that the opening between the barrel and bolt must be 10 inches in order to permit feeding, the bolt must travel a total of 11.9 inches (0.993 foot) before it is stopped by the backplate buffer. Fig. 2-27 shows that the bolt travel at the end of the acceleration period is 0.280 foot and the bolt must travel an additional 0.173 foot.

The motion of the bolt after acceleration may be determined bv the same methods as used for the

barrel motion. (Cf. fig. 2-31.) The first step is to draw a horizontal line at 60 feet per second to show the free bolt velocity. At the end of the

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