RX-79G said:
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.
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.
Vern Humphrey said:
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.
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.
RX-79G said:
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.
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.
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