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Figure 1-23. Free Bolt Momentum for First 0.010 Second.

exactly the same for advanced primer ignition as for plain blowback. However, it must he remembered that at the instant the propcllant charge is ignited, the bolt is moving forward and has a momentum equal to one half the total change in momentum which is produced by the propcllant explosion. At any instant after ignition of the propcllant, the free momentum of the bolt will be the sum of its initial momentum and the change in momentum produced by the impulse of the pro-pellant explosion.

As has been shown previously, the total change in momentum produced by the propellant explosion is expressed by equation 1 2 as:

MDVp+4700 Mc

Therefore the initial forward momentum of the bolt is

Since this momentum is directed forward, its sign is negative. Before the projectile leaves the muzzle, the momentum change produced by the impulse of the propellant explosion is:

Accordingly, the free momentum of the bolt at any instant during this time will be the sum of its initial momentum and the change in momentum resulting from the impulse of the propellant explosion. That is:

Equation 1-19 can be used to plot a graph of free bolt momentum versus time for the period before the projectile leaves the muzzle. For the cartridge and barrel on which fig. 1-10 is based, the equation is evaluated as follows:

l (.29X2750+4700X.070)J

The curve obtained by using this relation is shown in fig. 1-22. The same curve is also shown in

MAX. VELOCITY OF FREE REC0IL(2I.7

TIME (SECJ

0 0

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