Physics and Five SeveN operation.

Discuss the FN Five-seveN line of pistols and accessories.

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galexander
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Physics and Five SeveN operation.

Post by galexander » 25 Nov 2015, 11:00

I am afraid that I confuse easily. I am also not terribly good at finding info on this forum. I apologize for the latter.
I had originally thought that bullet friction kept the gun from beginning to cycle until the bullet exited the barrel. The FN patent 5,347,912 only shows and speaks of the bullet at a stand still and then gone. Roughly, what it the ratio of the force on the bolt face vs the bullet friction force on the barrel? Why did they give the mechanical advantage to the slide on the lever? Can anyone explain what they are saying in the paragraph in column 2 at point 30? "More over, in the case of firearms using cartridges with a neck, the slide also decelerated due to the propulsive force of the pressures prevailing in the chamber."
I notice also that the original EFK suppressor barrels were longer than they needed to be to fit on the suppressor. EFK told me that the government specified that length for reasons they didn't know. What is the implication of longer barrels on operation?
Thanks in advance. My head hurts.

Here is a PDF of the patent I have assumed is for the Five SeveN operation.
https://www.google.com/search?q=US53479 ... 8&oe=utf-8" onclick="window.open(this.href);return false;

PS Last winter I ask EFK to make some 6" barrels because I wanted to experiment. I was assuming that the lower uncorking pressure would effect the operation. Then it occurred to me that it was unlikely that the operation was entirely blowback because the bullet friction in the barrel couldn't be greater than the force on the 'bolt face' and also with the mechanical disadvantage the barrel has on that lever, it couldn't hold the slide in place until the bullet exited. I was rather disappointed because this meant the operation was more complicated than I originally and foolishly imagined. Of course, Jay's references to the timing issues should have made it obvious, but hope springs eternal.... until reality slaps you.
Last edited by galexander on 28 Nov 2015, 06:32, edited 2 times in total.

NLVMike
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Re: Physics and Five SeveN operation.

Post by NLVMike » 27 Nov 2015, 21:20

Wow. All good questions, and I can see why your head hurts. You refer to a specific patent, even by page number, like it is a document we are all familiar with. I have not seen it and cannot find a link in the forum wiki. If you have such a link, send it up. I would love to see it. We have a couple of pros here that may have some answers, but I am not that engineer.

good luck.

galexander
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Re: Physics and Five SeveN operation.

Post by galexander » 28 Nov 2015, 06:17

I am just posting this reply so that it will be obvious that I added the patent link to my original post. You are correct in that I had assumed many were familiar with it.
https://www.google.com/search?q=US53479 ... 8&oe=utf-8" onclick="window.open(this.href);return false;

Posting a question usually induces me to finally really work on the answer myself. I suppose that over all it is still fairly simple. For some reason just the blowback from the gas in the chamber and barrel is not appropriate to operate the action. (Can anyone speak to that?) The lever which they now call a cam converts a large fraction of the bullet barrel friction to slide motion resistance until the cam disconnects from the slide (or the bullet exits). The patent kind of makes it sound like it is just the barrel inertia involved, but it must be that bullet barrel friction also as the barrel inertia wouldn't be enough resistance, no?

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Re: Physics and Five SeveN operation.

Post by panzermk2 » 28 Nov 2015, 10:27

It has to do with blowback guns normally having fixed barrels.

The FsN is a blowback but uses the barrel movement to create a delayed blowback allowing time for the chamber pressure to drop before the slide starts extracting the case.

It's a brilliant idea that amazingly was not though of until FNH did.

It's a perfect system for dealing with the very hi but very short pressure curve of the 5.7 and a reason why you see so few 5.7 pistols out there.
The 2 are perfect together.

The patent has been a great source of consternation for other firearm manufactures looking to create a delayed blowback system as simple, compact and performing as the FsN's.
Jay Wolf
Pr. Elite Ammunition

"Engineers, the oompa-loompas of science!"

Be'ein Tachbulot Yipol Am Veteshua Berov Yoetz
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galexander
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Re: Physics and Five SeveN operation.

Post by galexander » 28 Nov 2015, 10:55

The barrel and slide are moving (albeit at different speeds proportional to their position on the cam) before the bullet exits the barrel? The cam connection from the slide to barrel only slows the slide to the point that the case is not extracted too far too fast while the pressure drops? About where is the bullet when the cam releases the slide?
If I remember correctly you were/are considering a 7" barrel. What are the implications of longer barrels on operation? I imagine that it necessarily increases the momentum transmitted to the slide but does it also retard the motion longer (in the case of the cam not releasing the slide until after the bullet exits).
I guess mostly what I am looking for is the order of events, the events being - slide motion start, bullet exit, cam slide disconnect.
Last edited by galexander on 29 Nov 2015, 11:10, edited 1 time in total.

GONRA
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Re: Physics and Five SeveN operation.

Post by GONRA » 28 Nov 2015, 14:48

panzermk2 sez: "It's a brilliant idea that amazingly was not though of until FNH did."
GONRA sez: 9mm Parabellum caliber MAB Model R (1960's era) in my Reference Collection has the SAME spring loaded barrel mechanism.

Technical note - waaaay back then, MAB made small batches (50's) of 9mm Parabellum caliber MAB Model R's.
A 1960's (?) era National Automatic Pistol Collector Association Monthly Newsletter article has all the info.
Each batch hada different mechanical action, but was still stamped MAB Model R so it gets confusing.
One way or another, mine came from a batch that (strived to) operate EXACTLY same as the FN pistol.
I shoot the lightest handloads that functions, 'cause its obviously "blowback"
NOT "cartridge case / chamber wall friction retarded blowback" as intended.

Problem is - 9mm Parabellum IS NOT the cartridge TO REALLY EXPLOIT this mechanism!!!

5.7x28FN is. FN guys had the freedom to design cartridge
(longer, thicker cartridge case walls so "axially stronger" don't forget the coating!)
all as a sorta "package" - THAT's why it all verks out (most of the time anyhow.)

GONRA believes we REALLY need a short recoil locked breech pistol to exploit this cartridge....

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panzermk2
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Re: Physics and Five SeveN operation.

Post by panzermk2 » 29 Nov 2015, 14:53

GONRA wrote:panzermk2 sez: "It's a brilliant idea that amazingly was not though of until FNH did."
GONRA sez: 9mm Parabellum caliber MAB Model R (1960's era) in my Reference Collection has the SAME spring loaded barrel mechanism.
It acts like but does not function the same, hence the FNH patent.
GONRA wrote: GONRA believes we REALLY need a short recoil locked breech pistol to exploit this cartridge....
NOPE total failure if you try. This was clearly demonstrated with the BOZ round. The BOZ was a PDW round developed at the same time as the 5.7 and 4.6. Even after machining more then half the slide away to reduce mass on both Glocks and 1911's the recoil impulse was so fast and so short the slides would short stroke even with 4 pound springs and still the breach face of the slide would last about 200 rounds before cracking from the impact of the case.

This is the biggest issue delaying the brand new 5.7 caliber pistol being worked on right now.
Jay Wolf
Pr. Elite Ammunition

"Engineers, the oompa-loompas of science!"

Be'ein Tachbulot Yipol Am Veteshua Berov Yoetz
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bayside
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Re: Physics and Five SeveN operation.

Post by bayside » 01 Dec 2015, 07:57

galexander wrote:I am afraid that I confuse easily. I am also not terribly good at finding info on this forum. I apologize for the latter.
I had originally thought that bullet friction kept the gun from beginning to cycle until the bullet exited the barrel. The FN patent 5,347,912 only shows and speaks of the bullet at a stand still and then gone. Roughly, what it the ratio of the force on the bolt face vs the bullet friction force on the barrel? Why did they give the mechanical advantage to the slide on the lever? Can anyone explain what they are saying in the paragraph in column 2 at point 30? "More over, in the case of firearms using cartridges with a neck, the slide also decelerated due to the propulsive force of the pressures prevailing in the chamber."
I notice also that the original EFK suppressor barrels were longer than they needed to be to fit on the suppressor. EFK told me that the government specified that length for reasons they didn't know. What is the implication of longer barrels on operation?
Thanks in advance. My head hurts.

Here is a PDF of the patent I have assumed is for the Five SeveN operation.
https://www.google.com/search?q=US53479 ... 8&oe=utf-8" onclick="window.open(this.href);return false;

PS Last winter I ask EFK to make some 6" barrels because I wanted to experiment. I was assuming that the lower uncorking pressure would effect the operation. Then it occurred to me that it was unlikely that the operation was entirely blowback because the bullet friction in the barrel couldn't be greater than the force on the 'bolt face' and also with the mechanical disadvantage the barrel has on that lever, it couldn't hold the slide in place until the bullet exited. I was rather disappointed because this meant the operation was more complicated than I originally and foolishly imagined. Of course, Jay's references to the timing issues should have made it obvious, but hope springs eternal.... until reality slaps you.
The action is a delayed blowback design. It relies on the fact that the bullet will be accelerated so fast that the inertia of the barrel and slide assembly being much greater than the inertial impulse of the bullet will result in the bullet moving almost entirely out of the barrel prior to the beginning movement of the slide/barrel, delay lever, etc. The rearward impulse must also be strong enough to cock the hammer, and the spring force returning the slide to battery must be strong enough to strip a cartridge from the magazine and also to force engagement of the extractor. The lever that is talked about has the effect of stopping the rearward motion of the barrel.

The essence of the function of a blowback design is that the barrel will stay in battery with the breechblock of the slide long enough for the chamber pressure to drop to a safe level to allow case extraction, which is accomplished using recoil energy. By delaying the uncoupling of the barrel from the breechblock (the slide) pressures drop farther than they would be if a simple blowback design were in use. In a simple blowback design, the barrel is fixed. In a delayed blowback design the barrel recoils. Short and long recoil systems keep the barrel and breechblock physically locked together for a time and do not rely as much on timing.

When they are talking about part 30, this is likely stating that the friction of extraction of the case from the chamber will also slow down the rearward motion of the slide. While under pressure the case is gripped by the chamber. So this suggests that the slide is moving prior to the pressure in the case dropping to ambient pressure. FN repeats several times that the cases are specially coated. I suspect that the only part specially treated is the case neck. Fired cases are noticeably longer than unfired cases. FN is also VERY specific in their instruction on how to clean the pistol. As is the case with all semi-automatic cartridges there should be no oil or excess case lube on the case prior to it's firing. The presence of oil can dramatically influence chamber pressure and interfere with reliable operation. FN specifically states there should be NO oil or lube on the bolt face. Oiling of cases IS a Proofing technique as it dramatically increase the pressure on the chamber.

The spring that keeps the lever in contact with the slide is fairly strong and has to have that force overcome during the combined recoil of the barrel and slide as they move together. The 5.7mm round has an operating pressure in the vicinity of 50,000 psi. So the forces that are created are very quick. It is the inertia created by the acceleration of the bullet that provides the operating force. The friction force of the bullet being engraved by the rifling is minimal. The recoil spring must also be able to return the slide to full engage with the barrel while also causing the detent action of the extractor to ride up over the rim of the cartridge case so as to allow the extractor to pull the case from the chamber in a rearward motion until it encounters the ejector, and is thus thrown out of the ejection port.

The effect of the delayed blowback design is to allow a lighter mechanism where TIMING is critical to ensure proper function as well as the amount of ENERGY produced. The muzzle energy of the bullet is the same as the energy that the pistol mechanism has available to it to affect movement while operating various features such as cocking the hammer and adding tension to recoil spring. The resistant mass, of the slide and the rest of the handgun absorbs some of the energy except for that which is surplus to the action of the slide and is the felt recoil from firing a round. Each of the resistive elements extracts a portion of this energy, but some is imparted to the pistol frame by the action of the barrel stop, other energy is used to cock the hammer (and tensioning the hammer spring) and the rest is transmitted to the frame as excess unused energy.

The essence of these effects is that the bullet will leave the barrel while the barrel and slide remain in battery as the assembly travels a short distance and then the barrel's movement is halted, allowing the stored energy of the slide to operate the ejection and reloading of the cartridges. It's readily apparent that the physics involved are understood in great detail by the manufacturer. As with all recoil operated actions the inertia (measured as Muzzle Energy) has to be within certain limits for the pistol to function correctly. As a result of the spring mechanisms the recoil/muzzle energy felt by the shooter is spread over a longer time, and thus is less noticeable.

Does this help clarify your understanding?

galexander
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Re: Physics and Five SeveN operation.

Post by galexander » 03 Dec 2015, 07:03

bayside: Yes, it does. My general conception of the operation has been corrected with this thread, but I have a of cogitating yet to do. I'd love to see a computer model with the times, forces, and velocities, quantified, but I doubt that will ever happen. Thank you.

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Re: Physics and Five SeveN operation.

Post by bruteandbear1 » 03 Dec 2015, 13:50

Gonra sez

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