FN FiveseveN mech??


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Handy
January 8, 2003, 11:49 AM
Been posting in various places trying to find out how the fiveseven works. I understand it is mechanically delayed blowback, but that the system is new and unrelated to the Kiraly, Benelli, HK or MAB methods.

Does anyone know, or has seen the parts, or know where a part diagram is? Thanks.


(Please don't turn this into a pointless debate about 5.7 ammo. I certainly don't care and it has nothing to do with the question.)

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GooseGestapo
January 8, 2003, 02:42 PM
I've handled one before, seen demo firings, and dry fired it-don't want one,would not buy one.

Yes it is a delayed recoil inertial system, not quite a "blow back". It is more like the CZ-52, but again just enough different to avoid patent/design licensing concerns. The cartridge is basically a rimless K-Hornet with shortened neck. I have a few spent rounds (cases) I picked up while shooting a PPC match at the GPSTC (Ga Public Safety Training Ctr.) range back in Sept (were obviously left after a qualification or testing). The feedback I'm hearing from the Duluth P.D. is that it lacks the punch of the .40S&W. At last contact, the few in use are by field supervisors. Will not likely see more. A recent shootout resulted in a ricochet round from the FiveseveN hitting a female officer in the rear-end, wounding her. (link in AJC has expired accessing archives requires subscription fee) Lack of punch and excessive penetration combined with high ricochet potential is discouraging use in urban environment of Duluth (sounds like 9mm w/FMJ, huh?). It would probably be a good combo if a soft point load was available. But just as I don't envision the Taurus .17 rimfire or .22 Hornet becoming popular L.E. gun/ammo, I don't see much future in the 5.7.
Who knows, the .17HRM might just be the next rage in L.E. armament. Taurus only needs to hire a P.R. firm, and produce a Clint Eastwood/Mel Gibson movie featuring it; then anything would be possible !!
BTW the sample I looked at had a 17-20lb trigger pull !!!!
I was more interested in cartridge than the gun. Ammo is really cute!, would make a nice varmint round with 35-40gr balistic tips.

Handy
January 8, 2003, 07:15 PM
Thank you!

It's funny that FN seems confused about their own weapon (they refer to it as delayed blowback on their website and press releases). But it's not if the barrel moves. I guess it's not surprising they went with a CZ-52 type setup, the round has its similarities as well.

Higgins
January 8, 2003, 08:38 PM
Handy, nice to hear from you over here at The HighRoad. I recall a number of posts from you at TFL. Like you, I have an interest in the various operating systems of different firearms. You've answered some questions for me in the past, I believe. Maybe I can return the favor here.

As for the FN 5-7, I went through this same pursuit a few months back. Like you, I just wanted to know how the 5-7 works, given that FN advertises the system as a unique form of delayed-blowback.

Anyway, after much searching, I managed to find what I'm pretty sure is the US patent for the FN's mechanism.

With all due respect to GooseGestapo and unless my information is wrong, the 5-7 appears to work nothing like the CZ-52. No locking rollers. As you know, the CZ-52 is a pure recoil operated mechanism whereby the locking of the slide and barrel for a short distance are accomplished by rollers.

The 5-7 mechanism does appear to be unique. It sits somewhere between a recoil mechanism and a delayed-blowback mechanism. Like recoil, the 5-7's barrel moves during cycling of the mechanism, but unlike recoil the barrel and slide are never really "locked" together. Like delayed blowback, the 5-7's slide is heal closed only by the recoil spring and a mechanical disadvantage holding the barrel against the slide. Again, though, unlike traditional delayed-blowback weapons, the 5-7's barrel is not fixed.

Okay, enough prelude. Here is how I understand the 5-7 to work. The barrel and slide are "linked" by a lever. Before the slide can travel rearward, the lever must first rotate towards the shooter thereby releasing the slide. However, the lever is held rotated forward by the barrel. When the 5-7 is fired, the bullet catches the rifling in the barrel. The friction between the bullet and rifling in the barrel is enough to create a force which wants to push the barrel forward. (Think Savage pistol, where the bullet's friction with the rifling prevents the barrel from rotating to release the slide). The barrel being held forward means that the lever cannot rotate reawards, which means, in turn, the slide cannot be released rearward. Thus, the slide is delayed from opening the breach until the bullet leaves the barrel. Only once the bullet leaves the barrel does the friction holding the barrel forward cease.

It's a delicate balance, as most delayed-blowback mechanisms are. The mechnical lever delay is setup so the friction of the bullet traveling down the barrel is sufficient to hold the breach closed. Once the bullet is gone and this force is gone, the remaining case pressure is enough to open the slide and cycle the action.

A picture (or diagram) is worth a thousand words. Unfortunately, I don't have either that I am able to post.

This is my understanding of the 5-7. If I am wrong, someone please let me know.

Hackworth92FS
January 8, 2003, 09:07 PM
I was just wondering how accurate the FN Five seven was. It seems like its a very high velocity round.

Handy
January 8, 2003, 09:21 PM
Hey Higgans, nice to hear from you.

That's interesting. I can see why it might be thought of a DB, but in reality it sounds like a recoil pistol. Wouldn't a Beretta also have barrel friction acounting for some of its lockup time? I think GG's comparison with the CZ-52 is reasonable.

Maybe the reason it is a delay has more to do with the dynamics and dimensions of the 5.7 cartridge. A pistol cartridge may be too short and slow to put adequate forward pressure on the barrel.

FNs method may be novel, but not very interesting. Its main advantage is likely that it's a low cost design that contains such high pressure. And recoil abatement should be good, too. But moving barrels seem passe'.


This is something of a relief. I think I've come up with a simple, fixed barrel delay system that works with only two moving parts (including the slide). I needed to know if I had just duplicated FNs work before I put any energy into the project (a new top end on a 1911 frame).

Higgins
January 8, 2003, 11:26 PM
Yeah, Handy, the 5-7 mechanism didn't really fascinate me all that much either once I learned more about it. As I recall from something I read on it, the design was pretty much developed around the cartridge - something to do with the round not capable of cycling a full weight slide in a locked breach, recoil mechanism - or something along that line. Which is also why the 5-7's slide is so light - plastic over an inner thin steel sleeve. In any case, unique, but not my cup-o-tea.

Like you, moving barrels seem to me a weakness in most handguns designs, which is why delayed blowback designs, which allow fixed barrels, would seem the way to go with a more accurate design. However, most delayed blowback designs - P9S, B76 - are complex and involved to mfg.

Sounds like you've got some ideas of your own. I've thought maybe a Kiraly bolt variation could be done and done simply in a handgun (a la a certain French rifle). The other thought - although a recoil mechanism - is a modern update of the Lahti, which also permits a barrel which doesn't move with respect to the slide/sights.

I don't want to steal your thunder, but I would like to hear what you've come up with in the way of a new fixed barrel mechanism and how you plan to carry it out. I'm always curious to understand new design ideas, especially if they take simplicity as their starting point.

If you have a moment, drop me an email or personal message and fill me in on what you are cooking up. Thanks.

Handy
January 8, 2003, 11:36 PM
Speaking of the Lahti, the Luger system also seems useful in that all the important stuff is connected together. The toggle is the problem.

My basic idea is possibly original enough that I'm going to shut up about it until I know more about patent law. I think I need to mail myself a copy (and draw it all out, too.) I'll try and keep you posted.

The drawback to the kiraly is where to put the lever(s) in a pistol frame and slide?

Higgins
January 8, 2003, 11:50 PM
Handy, I can appreciate your desire to keep things under wraps until you are further along with it. I'd probably feel the same way.

You do have me curious however, and I'd appreciate you filling me in on your idea once you feel comfortable doing so - whenever that may be.

I look forward to hearing from you and good luck. :)

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