Over the years I've spent on the gun boards, I've seen many a discussion/debate/flame war over straight blowback vs recoil operated designs, mostly centered around how "different" they are.
But, are they...really...that much different?
First, let's take a look at straight blowback operation from a physics standpoint...specifically Newton's 3rd Law of action and reaction and how it relates.
Bang! Expanding gases and pressure accelerate the bullet. Assuming a condition of zero headspace, the slide is accelerated in the opposite direction at the same instant...because force forward is force backward. As long as there are two interacting objects and two forces, you have an action-reaction system. In other words, the straight blowback is also recoil operated.
For this reason, I like to think of the straight blowback as Unlocked Breech Recoil Operated.
Now, for the other one.
Bang! Gases accelerate the bullet, and assuming the same condition of zero headspace, the slide starts to accelerate in the opposite direction at the same instant. So far, the two are exactly the same in operation. The difference lies in the method used to delay the opening of the breech until pressures have fallen to a safe level. At this point, please note that "Safe Pressure Level" doesn't necessarily mean atmospheric. It means the level below which the case won't blow out.
The unlocked breech uses slide mass and spring tension to achieve this delay. The locked breech example uses a mechanical connection between slide and barrel with the slide pulling the barrel backward with it for a brief instant, giving the bullet time to exit and pressures to fall off...usually to atmospheric levels...or so close that it can be called.
The main delaying force in the locked breech example isn't the slide's mass nor the spring, nor even the barrel staying with the slide for the 1/10th inch of travel needed to give the bullet time to exit. The strongest delaying force is the bullet itself as it moves through the barrel on its way to freedom. Though all those things play a part, the bullet's influence outweighs all of them combined.
So, both are recoil operated...and both are blown back...and both slides continue their journey rearward on momentum generated by the initial, brief period of acceleration that ends with bullet exit.
But, are they...really...that much different?
First, let's take a look at straight blowback operation from a physics standpoint...specifically Newton's 3rd Law of action and reaction and how it relates.
Bang! Expanding gases and pressure accelerate the bullet. Assuming a condition of zero headspace, the slide is accelerated in the opposite direction at the same instant...because force forward is force backward. As long as there are two interacting objects and two forces, you have an action-reaction system. In other words, the straight blowback is also recoil operated.
For this reason, I like to think of the straight blowback as Unlocked Breech Recoil Operated.
Now, for the other one.
Bang! Gases accelerate the bullet, and assuming the same condition of zero headspace, the slide starts to accelerate in the opposite direction at the same instant. So far, the two are exactly the same in operation. The difference lies in the method used to delay the opening of the breech until pressures have fallen to a safe level. At this point, please note that "Safe Pressure Level" doesn't necessarily mean atmospheric. It means the level below which the case won't blow out.
The unlocked breech uses slide mass and spring tension to achieve this delay. The locked breech example uses a mechanical connection between slide and barrel with the slide pulling the barrel backward with it for a brief instant, giving the bullet time to exit and pressures to fall off...usually to atmospheric levels...or so close that it can be called.
The main delaying force in the locked breech example isn't the slide's mass nor the spring, nor even the barrel staying with the slide for the 1/10th inch of travel needed to give the bullet time to exit. The strongest delaying force is the bullet itself as it moves through the barrel on its way to freedom. Though all those things play a part, the bullet's influence outweighs all of them combined.
So, both are recoil operated...and both are blown back...and both slides continue their journey rearward on momentum generated by the initial, brief period of acceleration that ends with bullet exit.
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