The "Blowback" FiveSeven

Discussion in '5.7 X 28mm Club' started by Scott60, Mar 6, 2019.

  1. Scott60

    Scott60

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    The Fiveseven pistol is often referred to as being "blowback" in method of operation. The term "blowback" being a rather crude, usually pejorative term meant to denigrate a particular action as much as to accurately differentiate it's operating method from other types.

    The fact is, all recoil operated firearms are technically "blowback" whether pistol, rifle, or shotgun. Blowback is a rather poor description that implies a degree of uncontrolled explosive mayhem likely to cause damage, as opposed to "locked breech." A term that conveys a feeling that all is right with the world and the machines we call firearms.

    The Fiveseven handgun is no more, nor less "blowback" in action than is the Browning 1911, or Glock series. All three rely on thrust imparted to the breech face by the mass of the bullet moving rapidly away. Being much heavier, the bullet travels considerably farther before the slide begins to move due to energy transfer. Due to the design and cosmetic features of the Fiveseven, it can seem to be "blowback" because the barrel does not tip up, or rotate, or appear to be "loose" inside the action when the slide is retracted, and the locking arms cannot be seen indexed into the steel slide beneath the polymer slide cover.

    Non locked-breech pistols differ only from those with locked breeches, in that the breech face is allowed to separate from the barrel earlier in the post-pressure phase of the cartridge firing. It is perfectly feasible to build an unlocked breech weapon in larger calibers such as 9mm and .45 auto, and even .30-06, and such systems are very simple, generally consisting of a large, massive slide or bolt of sufficient mass to remain static during the pressure phase of the firing cartridge. The downside is of course weight. The upside is a machine generally more reliable due to having just one part moving in just two directions. This is why the inexpensive Hi-Point pistol tends to be very reliable, yet heavy with most of it's weight being slide mass. This is why 9mm "carbines" that rely on "blowback" operation tend to be heavier than gas-operated systems, but also less expensive. Anyone who has ever handled military grade submachineguns knows they tend to be rather heavy - until you remove the bolt. In fact, the Browning 1917 and 1919A4 are examples of "blowback' actions chambered in the mighty .30-06! Due to the power of that cartridge, the 1919 relies on a massive bolt, combined with massive bolt carrier, plus the added mass of the entire barrel which is firmly mounted to the moving carrier. Browning had to come up with all sorts of interesting work-arounds to make such a system work - and he did. One ingenious part was the "accelerator" - a spring-loaded, hinged, arc-shaped lever that had to be "over-cammed" when the massive cycle mass pushed rearward, reducing thrust force to zero until the carrier came forward at which point the accelerator's powerful spring caused it to suddenly rocket upward and forward to give all that mass a "kick" into battery. This is one reason why modern light machineguns are gas operated...they need fewer band-aids to work, and they're lighter.

    Unlocked breech designs tend to have fixed barrels, while locking breach designs MUST have moveable barrels - either by tilting, sliding, or rotating, in order to make use of some amount of linear slide or breach travel as the barrel moves from locked to unlocked.

    The real reason behind using a locked breach, recoil operated mechanism is to get away with lower mass in the reciprocating parts, by using a delay mechanism to hold the breech face against the barrel longer, thus the term, "delayed blowback." Both systems work best when cycle mass is matched to power. It's perfectly possible to have a .460 Rowland "blowback" action (Mec Tech Carbine) as long as it has sufficient mass to hold things together until the bullet has left the bore. Whether straight "blowback," or delayed "blowback," both mechanisms rely on the breach remaining closed until the bullet has exited the barrel, bore pressure has abruptly dropped, and it's safe for the breach to begin opening, or more accurately, separating from the barrel.

    An unlocked breech begins to move as soon as enough energy is imparted into the cycle mass to move, and this is after the bullet has left the barrel, though bullets heavier, or moving faster than design weight will cause the cycle mass to move earlier.

    The term delayed opening, or delayed unlocking refers to the fact that the breech and barrel remain connected as a unit for a time after energy in the cycle mass has risen to the point of causing movement. This is where the "safety" factor we all desire comes from. The system isn't really "safer" per se, because just as over-powered cartridges in the unlocked breech system can cause "early opening leading to case failure, the same happens with locked breech systems. The purpose of a compensator on the .460 Rowland semiautomatic is to utilize a "gas delay" to extend the time the breech remains locked by reducing the total energy imparted to the cycle mass.

    The 1911 uses a Browning designed dropping barrel, with a link pin hinged to bottom barrel lug and slide stop pin. The link follows an arc as the barrel retracts, pulling it downward to disengage internal top barrel lugs from internal slide lugs.

    Glock uses a more modern, simpler design. The barrel has a bottom lug that slides horizontally over a hardened "locking block." The lug has an angled protrusion that indexes into a matching slot on the locking block, camming the barrel downward, separating it from the slide as the cycle mass unit moves backward.

    The Fiveseven uses another modern design - a cam lock system.
    FsN Cam Lock Retracted TV.jpg The photo shows the cam lock nearly at full retraction, held by a small spring. When locked, the cam is rotated up so the two locking arms on either side index into recesses in the slide body.
    FsN barrel lug.jpg The barrel has a large bottom lug with flat front face, and slotted rear. When installed, the barrel's front face is behind the cam lock, forcing it by action of both recoil spring and frame-mounted torsion spring, to push forward, forcing the locking cam locking arms upward.
    FsN LS Cam Lock up.jpg This photo shows the barrel located forward due to torsion spring force with no slide present. Notice the red line bisecting the barrel shroud join line, extending down in front of the large, orange safety dot. You can also see the cam lock is raised and the locking arms would be indexed into the slide's locking recesses were it present. At the rear the torsion spring can be seen pressing forward against the barrel's bottom lug - note the space between spring and frame crosspiece.
    FsN LS unlocked.jpg In this photo the cam lock can be seen down - retracted, and the red index line bisecting the barrel shroud join line is now located behind the large orange dot. The torsion spring is now pressed back against the frame crosspiece by the bottom barrel lug. The torsion spring is quite strong. The barrel need retract only a short distance due to the design of the cam lock. A short horizontal movement of the barrel lug causes the locking arms to swing a large distance. Compare the photos of lug up and lug down to see how far the locking arms move in permitting the slide to unlock from the barrel.
    Being locked together during the pressure phase of cartridge firing, recoil force must accelerate both the barrel and slide as a single mass the same as is done in a Glock or 1911.
    FsN slide locking lugs.jpg A bottom view of the steel slide reveals the locking recesses. The locking arms rotate upward to press into the slide recesses and hold it locked to the barrel until the two, together have recoiled a short distance - just as the Browning system does by a different method. Is the cam lock as strong as the Browning link system....probably not; is it as strong as the Glock system? I doubt it, but then it doesn't have to be because it's part of a purpose built system that uses as small-base cartridge, firing a low mass bullet that produces limited breech thrust. The cam lock is perfectly adequate and quite strong for it's design purpose. If desired the concept could be scaled up for a larger cartridge with greater breech thrust.

    FsN RS a.jpg FsN LS a.jpg

    Hopefully, for those interested this clears up a long-standing, often repeated, misunderstanding of the Fiveseven handgun.
     
    Last edited: Mar 7, 2019
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  2. G33

    G33 Frisky! CLM Millennium Member

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    Mine is great.
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  3. DrewBone

    DrewBone

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  4. Bradd D

    Bradd D

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    You've been thinking about this for a while.
     
  5. bac1023

    bac1023

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    Blowback is a term used for firearms that don’t have a locking design.

    You can spin it however you want, but that’s what it’s used for. Glocks and 1911’s are not blowback handguns.

    When you pull the slide back, if the barrel locks with the slide for a split second, it’s no blowback. Otherwise it is. Don’t waste time and energy overthinking it.
     
  6. glock_collector

    glock_collector

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    its waaaaaay too late...^^^^
     
  7. ranger1968

    ranger1968

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    :agree:

    Well posted, and explained in less than a thousand words, too.
     
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  8. bac1023

    bac1023

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    Yeah well, I just saw it. Better late than never. :cool:
     
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  9. Borg Warner

    Borg Warner

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    My problem with the 5.7 pistol is that it's expensive for a plinker and it doesn't have well placed and large enough safety to be kept in cocked and locked condition for a defensive gun.

    I'd much rather have a Rock Island 22 TCM pistol which has the same if not somewhat better ballistics, but is based on the 1911 platform and is available with a 9mm barrel for almost half the cost of the Five/Seven pistol.
     
  10. zaitcev

    zaitcev

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    Another good definition of the blowback is a mode of operation in which the energy is delivered to the operating mechanism through the motion of the case. If the bolt thrust is counteracted by the mass of moving parts alone, it is referred as to "straight" or plain blowback. If the case bottom acts upon a system of mechanical disdvantage, it is called a "delayed" blowback. A locked breech action is one in which the case remains supported by the breech and is not moving when fired, until the pressure drops. Since there's no relative motion of the case versus the mechanism, the energy to operate it must be delivered by other means. A typical recoil operated gun is a subclass of locked breech.

    We can split these hairs a little further in interesing ways. For example, we may let only a part of the case to move. This is a locked breech action, yet it presumes a movement. Because of that a primer-actuated action is often considered its own class. But generally it is a locked breech type.

    In addition, the FN's cam system permits a hybrid, where a delayed blowback is implemented by tilting the cam, while barrel and bolt (slide) move together under recoil, but at different speeds. I don't know enough about the action to tell what exactly happens in it, and the OP's entirely too verbose theatrise does little to enlighten.
     
  11. Mr Meeseeks

    Mr Meeseeks

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    And therein lies the rub. From my google-fu and discussions with a knowledgeable person on the topic, I’d say it’s safe to conclude that an OEM FN has exceptionally narrow design parameters relative to it’s true breach lock brethren. Warm loaded 40 grain bullets cause the neck to grow in unpredictable, extreme ways. This has even been reported with some of FN’s OE 40gr loads.
    If the goal is to shoot 27 grain ammo that the pistol was designed for, then it’s more than adequate. But the design limits reloading options, unless you’re willing to play the role of mad scientist.
     
  12. zaitcev

    zaitcev

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    Sounds like something a fluted chamber could fix. But we'd need aftermarket barrels for it. Ruger isn't going to do it, simply because of the cost.
     
  13. Mr Meeseeks

    Mr Meeseeks

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    According to a very knowledgeable person on here, a heavier recoil spring (and maybe hammer spring) should go a long ways toward mitigating or eliminating the issue. Since Ruger doesn’t use a bogus spring design like FN, it should be possible to retrofit heavier springs. I’m quite sure we will see posts with such a test within the next 6 months..