The Machine Gun

bolt reaches back plate

.009 .010 .oil .012 .013 .014 .015 .0*6 .017 .018 .0í9 .020 .021 .022

Figure 2 31. Effect of Bolt Driving Spring on Bolt Motion After Acceleration.

the minimum possible loss of time and energy. In the analysis of short recoil it was pointed out that, although the reversing action is accomplished almost instantaneously by causing the bolt to rebound from an extremely stiff elastic member, the impact is accompanied by a loss of energy with the result that the velocity of the bolt after impact will be at best approximately 70 per cent of its striking velocity.

Since the velocity of the bolt before striking the backplate is 51.5 feet per second, the momentum of the bolt is:

Assuming that the coefficient of restitution of the backplate is .70, the velocity of the bolt after impact will be:

V = .70 X 51.5=36.0 ( — The momentum of the bolt will then be:

velocity travel step 5

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