Physics of shooting a rifle

[tangolima]

The force that compresses the spring also asserts on the sleeve (action and reaction). It will accelerate backward as the spring is being compressed (F=m x a). The sleeve can't possibly be stationary.

Heavy sleeve/soft spring = slow sleeve/a lot compression. Light sleeve/stiff spring = fast sleeve/little compression. It is also possible that the spring bottoms out during recoil. It becomes a solid steel disc. That may well be the Benelli trick. The sleeve aquires the same speed of the receiver and is further accelerated by the compressed spring.

I think qualitatively we are taking about the same thing. Difference is in the quantities. The video clips are good. But they could be a bit over simplified for marketing purposes.

-TL

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[JohnKSa]

The sleeve can't possibly be stationary.

Yes, of course, there will be some acceleration on the sleeve before the acceleration cycle of recoil finishes because the spring is very stiff, but the point is that the sleeve is propelled by the spring, not by the impulse of recoil. It's absolutely clear in the videos that initially the sleeve stays more or less still (note that I've been saying "more or less still" repeatedly throughout this exchange) during the first part of recoil which is not how a momentum/recoil operated system works.

In a momentum/recoil operated system, the moving parts get all their kinetic energy before the bullet leaves the barrel from conservation of momentum. In an inertia operated system, the moving parts get their kinetic energy mostly after the bullet leaves the barrel from the potential energy of a spring. It's a fundamental difference and it is clearly visible in the videos.

If the gun were recoil operated, the bolt would move with the gun as soon as recoil begins and then continue rearward when the shooter's shoulder decelerated the gun. Instead, it does not move with the gun in recoil, it initially stays more or less still and that inertia compresses a spring which then drives the bolt rearward when it decompresses.

The video clips are good. But they could be a bit over simplified for marketing purposes.

They actually show the system in operation. No way to oversimplify that--you can see what is actually happening as the system operates.

The explanation Benelli gives (and the one I've given) is consistent with physics and with what can be seen visually in the videos. There's no need to try to cast about to come up with some other explanation for how it works--we can see how it works in the video and we can hear how it works from the people who designed the system and worked out the physics to make everything function properly.

I think qualitatively we are taking about the same thing. Difference is in the quantities.

I think that if you can convince Benelli they don't know how their system works, you may be onto something. Until then...

[tangolima]

Ok John. Let's set this aside and move on to something else, shall we? Thanks.

-TL

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[tangolima]

Originally Posted by tangolima

When I first started handloading (I prefer that to reloading), I had a mentor. He quite liked using slower powders for pistols. The recoil is milder. Instead of snappy shove, it would be a gentler push, so he told me. So I started with just that, slower burning powders.

However I found it was quite the opposite. The recoil with faster powders, similar bullets and MVs of course, is actually more agreeable.

How so?

-TL

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I'm answering my own question. Hopefully the discussion can be restarted.

The recoil follows the principle of conservation of momentum. The momentum comes from the projectile and the gas existing the muzzle. The mass of the gas equals the powder charge. The speed of gas is generally higher than the projectile, so the gas' momentum is significant part of the equation.

Slower powder requires higher charge for the same MV. It has flatter pressure curve, which often leads to higher muzzle pressure. The gas exits at higher speed as result. That's why slower powder tends to have more recoil force, louder report, and more visible muzzle flash. True that the peak pressure is lower than faster powder, but human body most certainly can't tell the difference for events all happen within a minisecond or two.

Actually I managed to use this mechanism to improve one of my loads. I experimented with .22TCM9R. Found a conversion upper for Glock 23. The recoil spring is very soft, and yet it doesn't cycle reliably, even when the load is maxed with bullseye. The MV is crazily high. But with the light 40gr bullet, the momentum is just not enough. I switched to Ramshot enforcer, and it worked. It is loud with big ball of fire. Basically the slide is rocketed backwards by the hot gas to complete the cycling.

Okay, next rabbit hole is canting of sight and its effects on POI, if there is still interest from the forum.

Before going down the hole, let's take a sidetrack. Why is it dangerous to shoot a gun under water?

-TL

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