Inertial firing pins - less drop safe hammer cocked?

Discussion in 'Handguns: Autoloaders' started by RX-79G, Aug 25, 2016.

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  1. RX-79G

    RX-79G Member

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    A little background: Inertial firing pins, which not all modern autoloaders have, were created by Browning to allow hammer fired pistols to be carried with the hammer down on a live round. The inertial pin is short, so when the hammer rests on it there is room to retract into the slide without touching the primer.

    And they work. If you drop a decocked 1911, PPK or Beretta 92S on the hammer the gun will not fire - despite not having automatic firing pin blocks.

    However, in testing and reality, most 1911s with steel firing pins will fire if dropped muzzle down on a hard surface. This isn't a super dangerous situation as the bullet is going into the ground, but still not awesome.


    But an inertial pin hitting a primer hard enough to fire requires that it gets up to speed. When the hammer is down, the firing pin is placed much closer to the primer, and has less room to accelerate (relative to the primer) when dropped.

    So would a 1911 that would fail a CA drop test with the hammer cocked, pass if the hammer was down? (Or any other pistol with the same firing pin configuration.) It seems like it would be less likely since most guns end up with the FP barely 1mm off the primer when the hammer is against them.
     
  2. MikeJackmin

    MikeJackmin Member

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    Sounds reasonable.

    I wonder in an unlocked 1911 would fire at all under that condition, or if the slide would not go out of battery and absorb most of the impact force in the process. A cocked and locked series 70 gun could fail as you described, but uncocked also means unlocked.
     
  3. Zerodefect

    Zerodefect Member

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    If I'm climbing a ladder, I'll just choose my Glock (striker safety block) instead of my 1911. Problem solved. You can always choose an even lighter FP or a stiffer FP spring for more inertia safety. Even a retention strap on your holster.

    Being that I care about my safety, I actually tested this with a turdy Kimber with the shwartz removed and a blank. It's nearly impossible to get a 1911 to go off by dropping it. Mine would not. Had to recrown the barrel and refinish the slide.
     
  4. RX-79G

    RX-79G Member

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    MikeJackmin - excellent point about recoil pistols and muzzle drops. A PPK would not act that way with the fixed barrel.
     
  5. Vern Humphrey

    Vern Humphrey Member

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    An additional 0.1" of firing pin travel, under the influence of gravity would yield about 1 fps additional velocity. I don't think hammer cocked or hammer down would make a difference. A stiffer firing pin spring would easily prevent accidental discharges from any reasonable drop distance.
     
  6. RX-79G

    RX-79G Member

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    Not following your math. It isn't one gravity. To calculate the velocity you'd need the upward velocity of the gun as it bounces plus the initial velocity of the firing pin going down. If the firing pin starts closer to the primer there is less time for the guns upward velocity to develop before the pin hits.
     
  7. Zerodefect

    Zerodefect Member

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    So:

    Assuming a 1911 can fall exactly on it's nose and the concrete stops it immediately.

    -how much does the FP weigh?
    -how much force does it require for a decent FP spring to compress?
    -how much force does it take to dent a primer?

    -how far do I have to drop a 1911 to get enough momentum in the firing pin to overcome the spring force and the force required to activate the primer?

    Would be a fun, if simple, physics problem for the kids.
     
  8. Vern Humphrey

    Vern Humphrey Member

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    First of all, the question I'm addressing was not "how fast and how much does the gun rebound?" It was "Does the firing pin have significant additional velocity if the hammer is cocked, versus hammer down on the firing pin?"

    Assuming the firing pin to weigh .01 lbs, then the additional energy of the firing pin from a 0.1 inch additional fall would be negligible -- virtually too small to measure.
     
  9. RX-79G

    RX-79G Member

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    Well, we know it can happen because there aren't any steel series 70 type 1911s that passed the CA drop tests.

    The other problem is that the surface that the gun hits is going to greatly change the impact velocity on the pin. Concrete vs. wood vs. linoleum will all behave differently.

    So I don't think it is actually all that easy to figure out because of the way floor materials reflect or absorb energy.


    All I was getting at was that starting with the pin closer to the primer gives less time for a major velocity delta to develop, and that most hammer down guns may be even more drop safe than they might seem from condition 1 1911 tests. Browning did not develop the inertial firing pin for Condition 1 carry, and it may be a poor choice for that type of carry.
     
  10. RX-79G

    RX-79G Member

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    Vern, I am not following how you are getting a velocity from a distance alone. Velocity comes from acceleration over a distance, and you don't have an acceleration number. It isn't gravity, but comes from the actual velocity the gun hits with and then bounces up with.

    The inertial of an inertial firing pin comes from how much velocity it was able to achieve in the 2mms sticking out for the hammer to drive. When you drop the gun it is like a hammer driving the gun into the pin, and the space between them is still necessary to cause velocity to develop between the gun and pin. In part because there is a spring between them.


    And maybe that's an easier way to think about this - if you took a static gun and hit the muzzle with a hammer, would it take less force to fire the primer if the firing pin starts farther away? I'm guessing "yes" because the gun has developed more velocity in those 3mms than it would have in 1mm.
     
  11. Vern Humphrey

    Vern Humphrey Member

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    First of all, the gun and firing pin ARE falling by gravity, so the Gravitational Constant, 32.2 f/s/s holds.

    Secondly the question was is there a significant difference between dropping the gun with the hammer cocked versus with the hammer down.

    The gun will not rebound FASTER based on the position of the hammer, now will it?

    Therefore the answer is to calculate how much additional velocity the firing pin would have with an extra 0.1" fall.
     
  12. Vern Humphrey

    Vern Humphrey Member

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    And the calculations show there is no major velocity delta – unless you call one foot per second a “major” velocity delta. And, given the low mass of the firing pin, there cannot be a “major” energy delta, either.

    In other words, hammer down or hammer cocked, makes no significant difference.
     
  13. RX-79G

    RX-79G Member

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    Vern,

    The important acceleration is not that of gravity. The important acceleration is the rebound acceleration off the floor.


    I think what is tripping you up is where the acceleration is coming from. The acceleration of any object going any velocity is essentially infinite if the object stops instantaneously. But nothing actually stops instantaneously, which is why the impact duration matters. Hitting a wood floor means less acceleration than concrete because the actual impact is spread over more time.

    Even short distances matter when you have especially hard impacts. Think crumple zones in cars.
     
  14. Walt Sherrill

    Walt Sherrill Member

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    I don't see how the hammer being cocked or NOT cocked makes any difference... as it's the firing pin itself that is moving inertially -- the hammer isn't really a big factor. (And being cocked would mean the hammer would have to overcome the sear that is in the way.)

    As is clear from my following comments, I have only a rudimentary understanding of physics, but it seems that the key factors at play are:

    1) how far the firing pin must travel to contact the primer with enough force to ignite the primer;

    2) the nature of the primer itself (as some are "harder" to ignite than others);

    3) the ability of the firing pin spring to resist the inertial movement of the firing pin; and

    4) how far the gun must drop to make the firing pin (step 1, above) move enough to ignite the primer (step 2).

    As others have noted -- things fall at the same rate regardless of their weight -- so the weight of the firing pin (wind resistance isn't a factor) -- shouldn't play much of a role.

    • The weight of the firing pin spring (it's measured strength to resist the firing pin when it's struck by the hammer, not it's actual [physical, material] weight) MIGHT be a factor.
    • It seems as though the shape/size of the firing pin tip could play a small role in terms of passing the inertial force to the primer, but I know ZILCH about primers and how they work, so that may be irrelevant.
    Seems as though all of those variables can change from event to event, and there are too many variables at play to make a general statement -- except when talking about 1911s without a firing pin block that are made to a general standard, like those that consistently fail CA drop test. :)
     
  15. RX-79G

    RX-79G Member

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    Walt,

    The hammer is a factor because when it is lowered it decreases the distance between the pin and the primer by pushing the pin into the slide, which you mention in 1).
     
  16. Vern Humphrey

    Vern Humphrey Member

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    The question does not address rebound acceleration. It ONLY addresses the difference between the hammer down or hammer cocked.
     
  17. Walt Sherrill

    Walt Sherrill Member

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    OK. That makes sense, but it can't have MUCH of a role (albeit SOME).

    The part I was responding to was slightly different, when the poster asked:

    Hammer cocked ought not have any effect on the firing pin. Hammer down? Maybe. Using your argument, things would change slightly: the distance the firing pin would have to travel would be slightly less, and the firing pin itself would meet likely meet a bit less resistance from the slightly compressed spring (which has been a bit compressed by the hammer) -- but I wouldn't know how to GUESS the effects of those changes. One factor (shorter distance to travel) MIGHT somewhat offset the other (less resistance to overcome.)

    We've got to be careful here, or we'll end up acting like a group of medieval clerics arguing about how many angels can dance on the point of a pin...

    (If the angels are at all like some of the very religious Protestants I've known, they probably don't dance...:) )
     
  18. RX-79G

    RX-79G Member

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    Vern,

    The question assumed that the reader understands the forces involved.


    You didn't seem to understand what I was saying about what causes muzzle drop firing, which would be important to understand before you could evaluate whether additional firing pin free run would be important or not. As you keep saying the force between the firing pin and gun is just one gravity, I keep trying to explain how it is not so you might be able to evaluate the topic accurately.

    I have no idea whether I'm right about the firing pin free run or not, but I do know that the firing pin doesn't strike at 9.8 m/s2.
     
  19. Vern Humphrey

    Vern Humphrey Member

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    And by my calculations, which consider the firing pin to be a free falling object, the hammer back state would result in about 1 fps in additional velocity for the firing pin. That translates into an almost undetectable increase in kinetic energy.

    And in answering the original question, it doesn't matter WHAT the impact velocity is -- what matters is how much FASTER is the pin from the cocked gun than from the gun with the hammer down.
     
  20. RX-79G

    RX-79G Member

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    I'm pretty sure the mass and velocity of the firing pin is not primarily what makes dropped guns fire. A pistol that will fire when dropped from 1 meter, as in the CA test does not have a firing pin that would ignite a primer if dropped from 1 meter with a spring on it. The pin wouldn't even touch the primer.

    What causes guns to fire when dropped is the gun bouncing up into the pin, not the pin running into a suddenly stopped pistol. The bouncing is why the distance to the pin matters.
     
  21. FL-NC

    FL-NC Member

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    In SF training we were taught that the Makarov isn't drop safe and should always have the safety engaged when a round is in the chamber.
     
  22. RX-79G

    RX-79G Member

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    That's interesting. I wonder if they said that because it had been tested, or just because of the type of firing pin it has? Its the same firing pin as an M16.


    Makarovs passed the CA drop safety tests.
     
    Last edited: Aug 26, 2016
  23. Walt Sherrill

    Walt Sherrill Member

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    I found the following on the net, re the CA drop test. Here's a link http://oag.ca.gov/sites/all/files/agweb/pdfs/firearms/regs/chapter5.pdf. See page 6 for specifics:
    12128. As used in this chapter, the "drop safety requirement for handguns" means that at the conclusion of the firing requirements for handguns described in Section 12127, the same certified independent testing laboratory shall subject the same three handguns of the make and model for which certification is sought, to the following test:

    A primed case (no powder or projectile) shall be inserted into the chamber. For pistols, the slide shall be released, allowing it to move forward under the impetus of the recoil spring, and an empty magazine shall be inserted. For both pistols and revolvers, the weapon shall be placed in a drop fixture capable of dropping the pistol from a drop height of 1m + 1cm (39.4 + 0.4 in.) onto the largest side of a slab of solid concrete having minimum dimensions of 7.5 X 15 X 15 cm (3 X 6 X 6 in.). The drop distance shall be measured from the lowermost portion of the weapon to the top surface of the slab. The weapon shall be dropped from a fixture and not from the hand. The weapon shall be dropped in the condition that it would be in if it were dropped from a hand (cocked with no manual safety applied). If the design of a pistol is such that upon leaving the hand a "safety" is automatically applied by the pistol, this feature shall not be defeated. An approved drop fixture is a short piece of string with the weapon attached at one end and the other end held in an air vise until the drop is initiated.
    The following six drops shall be performed:
    (a) Normal firing position with barrel horizontal.
    (b) Upside down with barrel horizontal.
    (c) On grip with barrel vertical.
    (d) On muzzle with barrel vertical.
    (e) On either side with barrel horizontal.
    (f) If there is an exposed hammer or striker, on the rearmost point of that device, otherwise on the rearmost point of the weapon.​
    The primer shall be examined for indentations after each drop. If indentations are present, a fresh primed case shall be used for the next drop.

    The handgun shall pass this test if each of the three test guns does not fire the primer.​

    Apparently, some guns do ignite primers with the spring installed. But a lot of guns aren't even submitted for testing... because the gun makers don't want to give up three handguns that are unlikely to pass the tests.

    Didn't you say the difference is almost undetectable? According to info on the 'net, most states who do drop tests don't test with the hammer cocked.

    Back to RX-79G's comments:

    The California drop test requires that the gun be dropped with any user-managed SAFETY mechanisms not engaged. CA doesn't test cocked and locked 1911s with the safety on; only with the safety off.

    It's not clear, from reading their documentation whether they test with the hammer down or back, but I suspect they do both. They certainly drop them in a lot of different ways, including upside down, sideways, flush, less than flush...

    I'll say it again: I have only a rudimentary understanding of physics, but...

    Whether 1) the inadvertent movement of the firing pin is due to inertia when the gun first hits the concrete or 2) whether the primer strike is the consequence of the gun and barrel bouncing against the firing pin after hitting the concrete, I would argue that the cause is the same. If the firing pin doesn't move forward (in relative terms), the primer isn't going to be struck.

    When the gun first hits, it stops -- but the firing pin and firing pin spring don't. Rebound acceleration was mentioned somewhere here. Aren't the firing pin spring and firing pin also going to rebound, too -- after a split second delay? And can't that second rebound also reduce the likelihood of the pin closing the gap? (The force already stored in the spring might also be pushing the firing pin away from the primer as the barrel and slide bounce...)

    If the gun barrel and slide hit flush against the concrete the whole slide assembly should move as a unit -- and only the firing pin (and firing pin spring) can move. If the firing pin travel is a consequence of the barrel and slide bouncing, the firing pin must still move, in relative terms, for the primer to be struck. But it gets more complicated if the rebound is where things happen.

    If the barrel and slide hit at a slight (or greater) angle, the barrel can/might unlock or begin to unlock from the slide and if the primer hasn't already been struck, the gap between breech face and primer can increase. But the firing pin can still move forward. CA doesn't test for this "off-vertical" hit, so it might suggest they don't consider it a risky issue.

    Given that the pin has to have moved through the breech face and be there with some force, I don't know HOW the barrel is going to bounce into the firing pin! Particularly if the pin movement is retarded by the firing pin spring. Given my meager understanding of physics, it seem to me that the firing pin's ability to jump of the gap is most likely to occur at the moment of impact (with a flush hit), rather than later... when the barrel must bounce against a firing pin that may also be bouncing as IT rebounds!!

    Maybe someone can explain the other ("rebound") possibility in a way that makes sense to us who are "physics"-challenged.

    .
     
    Last edited: Aug 26, 2016
  24. ATLDave

    ATLDave Member

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    NO. That is incorrect. The firing pin does all its acceleration while the gun is falling. What happens at muzzle-down ground impact is that the barrel decelerates essentially instantly, and the firing pin continues moving. While it moves, it is decelerating because the FP spring is working to slow it, but it may or may not have enough energy left by the time it reaches the primer to pop it.
     
  25. RX-79G

    RX-79G Member

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    Walt,

    In the first thing you quoted, I wasn't very clear, but I was trying to say that if you took a firing pin and spring out of the gun, put them in a tube so they would fall straight, and dropped them on a primer the primer wouldn't ignite. I don't believe the firing pin alone has enough mass to overcome the spring from just one meter.


    What I believe actually happens is that the gun and the firing pin could be seen as two objects falling one right after the other - like two super balls. The gun and firing pin attain the same velocity from falling one meter. Then the muzzle hits the concrete and the gun bounces, switching from moving straight down at 9.8 meters a second (since it fell one meter) to moving straight up at something less than 9.8 meters a second.

    Nothing can change direction 180° or come to a stop instantaneously, so it takes a certain amount of time for the gun to go from 9.8 down to whatever its new upwards velocity is. In the meantime, the firing pin hasn't struck anything yet, and is still moving down, but is slowing a tiny bit due to its spring.


    My thought is that if you dropped two super balls nearly touching each other, the trailing ball is going to hit the lead ball before it can fully rebound, so their relative velocities are going to be more similar and they will impact each other softly. But if you drop the two balls a couple of inches apart, then the lead ball has more time to fully rebound and start bouncing up before the trailing ball hits it. In that case their velocity difference is greater.


    In a gun, if the firing pin is compressed down closer to the primer, the firing pin impacts the primer earlier in the bounce - before as much upwards velocity developed, making the them crash at lower speed. Give the firing pin more space by cocking the hammer, and now the gun has the time and space it needs to complete its bounce get up to its upward velocity - causing it to hit the firing pin with a greater upwards velocity than if the firing pin were right behind it.

    To put some math on it, since hard concrete is going to absorb less energy than soft materials, we could guess that the gun might go from 9.8m/s velocity down to bouncing up at maybe 7m/s. If the firing pin is still going 9.8 and the gun is coming up at it at 7, then their impact velocity is going to be 9.8+7=16.8m/s. But if the firing pin is close enough to the gun primer, it will impact earlier and the bounce won't have happened as much, so maybe the gun is only moving up at 1m/s. 1+9.8=10.8m/s of impact velocity in that case, which is less likely to crush the primer than 16.8m/s.


    And that's why I think the Makarov passes 1 meter drop tests with the firing pin resting right on the primer, and 1911s fail with the firing pin pushed 3mm off the primer. More space to bounce equals more difference in velocity.

    This is also the reason hard surfaces (concrete) are going to be more likely to cause a drop fire - because metal objects bounce more from impacts with concrete than wood, increasing that upwards rebound velocity and taking less time to rebound.
     
    Last edited: Aug 26, 2016
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