Inertial firing pins - less drop safe hammer cocked?

[Slamfire]

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.

I would not count on that and something not taken into account is the varying sensitive of primers. Primers vary considerably in sensitivity within the lot. Incidental contact between something hard and a primer has the potential of igniting the primer. There are accounts where almost no energy was required to set off a primer.

Primer goes off in a Purse!

http://news.yahoo.com/blogs/sidesho...ide-woman-purse-shoots-her-leg-232052308.html

By Eric Pfeiffer, Yahoo! News | The Sideshow – Tue, Jun 12, 2012

A Pennsylvania woman was shot in the leg while shopping at a local department store on Tuesday. But in a nearly unbelievable twist, no gun was involved. Apparently, the woman was carrying the bullet in her purse, when it mysteriously exploded.

"She did not have a gun in her purse or on her," Montoursville Deputy Police Chief Jason Bentley told the Williamsport Sun-Gazette. Bentley said the woman, whose name has not been released to the public, "was not aware" she was carrying two or three bullets inside her purse at the time of the accident.
The 56-year-old woman was taken to a local hospital and was eventually discharged. In fact, the woman initially declined medical treatment, only heading to the Williamsport Regional Medical Center after her son reportedly encouraged her to do so.

"Something must of hit the primer of one of the bullets," Bentley said. "The bullet stayed in the purse, but its casing put a hole in the purse and caused a minor leg wound."

Bullets exploding outside of a gun are a rare occurrence but are not entirely unprecedented. In March, a bullet being used as evidence in a court case exploded in a bag and shot 20 feet across a courtroom. No one was hurt in the incident. It was surmised that the bullet exploded after its tip bounced against another bullet tip in the same evidence bag, according to the Telegram & Gazette.

Drake Oldham M1911 Drop testing

1911 Drop Testing

The original testing used a 9mm steel firing pin and a 9mm titanium firing pin. The firing pin hole was then reamed for a .45 sized pin and the tests were repeated with .45 sized steel and titanium firing pins. All of the firing pins were weighed prior to testing. A Wolff XP firing pin return spring was used for all of the testing. All of the cases used for testing used Winchester large pistol primers. The frame and slide were donated by Gary Smith at Caspian. The pistol was built using techniques learned from Larry Vickers and Bruce Gray. The pistol was tied to a section of 550 cord, looped over a pulley, and dropped onto common floor materials. The magazine was loaded with 8 dummy rounds to bring the pistol up to proper weight. Four floor types were selected. Concrete, Pergo, 5/8 plywood, and shag type carpeting. The thumb safety was left OFF as preliminary testing with the safety ON indicated that damage to the thumb safety, slide, and plunger tube would occur with only a few drops.

The hammer frequently dropped to the half cock notch during testing.

9mm STI titanium pin 2.17 grams
9 mm Caspian steel pin 4.45 grams
45 STI titanium pin 2.36 grams
45 Colt steel pin 4.30 grams.


I was amazed at how easily a Series 70 1911 could be drop fired. Steel firing pins and concrete are a bad combination. 9mm sized pins and titanium construction will add several feet to your safe drop distance. I will be running Wolff XP springs and a Ti pin in all of my Series 70 type 1911’s.
I have attached an Excel spread sheet with the results. You will notice a lot of “Did Not Drop” entries. I saw no reason to drop test a particular combination of firing pin and flooring if it was not firing at higher distances or on harder flooring. I did several drops at various distances to get an idea of safe drop distances. This was to account for hard or sensitive primers. Each primed case was dropped only once. Just in case you were wondering, the pistol sustained significant damage. The muzzle is distorted from being dropped. I had to turn down the outside diameter of the barrel three times just to keep the slide from locking up. The muzzle, magwell, and grip safety have some serious blending in their future. Nothing sounds worse than a 1911 hitting the concrete from 10 feet!

 

[Walt Sherrill]

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.

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.

The firing pin is accelerating while the gun is falling in both cases.

When the hammer is down, the firing pin is starting it's acceleration (inertial movement) from a slightly lower position -- and that means the firing pin has slightly less far to travel after the barrel has stopped. When the hammer is down, the firing pin must also move toward the primer against slightly less spring resistance, as the spring is already slightly compressed by hammer pressure and the weight of the firing pin before acceleration begins.

When the hammer is back, the the only pressure against the firing pin spring is the weight of the firing pin, and that pin has to travel a bit farther after the barrel has stopped, against greater spring resistance.

Whether those two "differences" really matter is unclear, but I think your description above ignores those differences.

 

[ATLDave]

Whether those two "differences" really matter is unclear, but I think your description above ignores those differences.

My statement was pretty limited. I simply stated that the FP did all its acceleration during the fall. The original post claimed (or appeared to claim) that the FP accelerated during the interval of time between when the gun muzzle hit the ground and the FP impacted the primer (or reached its furthest point of excursion). I pointed out that's not correct, and a bad start to the analysis. I "ignored" other differences because I wasn't talking about them.

I did not opine on whether a lowered hammer would reduce the likelihood of a discharge. I do not know. I will say I am skeptical that it makes any measurable difference, but only experimental data would make me confident.

When the hammer is down, the firing pin is starting it's acceleration (inertial movement) from a slightly lower position -- and that means the firing pin has slightly less far to travel after the barrel has stopped.

OK, so the fp under a lowered hammer has .10"(?) less potential energy, and its safe drop height (muzzle to floor measurement) would be increased by that same .10". Is that what we're talking about? Lowering the hammer means the gun can safely be dropped from a tenth of an inch higher?

When the hammer is down, the firing pin must also move toward the primer against slightly less spring resistance, as the spring is already slightly compressed by hammer pressure and the weight of the firing pin before acceleration begins.

I could imagine this making more difference. However, I tend to think that springs do more work as they get more compressed, and so the loss of deceleration by the FP spring is less than the proportional positional reduction. (I.e., lowering the hammer only trims off the "softest/easiest" portion of the spring compression.)

 

[RX-79G]

ATL,

The post you're referring to was where I was speaking about the firing pin and gun "accelerating" into each other from the reference point of the gun. From other reference points it looks different. From our reference point the gun is accelerating up into the firing pin.

And as I tried to illustrate in my last lengthy post, the difference in distances is only important because of how the gun bounces, not how far anything has fallen.

 

[ATLDave]

Even from the viewpoint of the gun, the FP is not accelerating from the point of muzzle contact. The FP spring is decelerating the FP.

 

[RX-79G]

Not if the gun is accelerating toward it. Because it bounced.

 

[ATLDave]

What is the coefficient of restitution of a 1911? What is its characteristic time in contact with a concrete or steel plate floor?

How much bounce velocity are you anticipating? And how long does it take it to begin actually moving upward?

 

[RX-79G]

Hardened steel on concrete? 50% Not sure. But when I drop steel tools on a garage floor, they definitely bounce if they hit square.

 

[ATLDave]

Do your tools bounce to fully half the height from which they were dropped?


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[ATLDave]

And do your tools have recoil springs in them that would compress on impact and keep the part of the tool hitting the floor in contact with the floor while it compressed and then decompressed?


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[RX-79G]

Nope. But a cocked and locked 1911 doesn't, either.


And screw drivers will bounce pretty high.

 

[ATLDave]

Screw drivers don't have any moving parts whose relative movement to one another dissipate impact energy. I've seen a few guns dropped on hard range floors. Haven't seen any bounce more than a few inches. I am skeptical that whatever bounce occurs in a 1911: 1) is anything other than a small fraction of the velocity of the FP or 2) happens quickly enough to meet the FP on its way down.


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[RX-79G]

Sure. I have no idea how much the slide itself will bounce, but that's the part we're concerned about, and even if it only bounces 20%, that still increases the impact velocity more than just the firing pin falling on its own.

A Makarov is all steel and has a fixed barrel, so it is going to bounce pretty good, but its firing pin passes. That's why I think the starting position of the firing pin might matter.


But it is just a theory to discuss. My take on it does make me even more confident carrying hammer down autos with no AFPBs.

 

[ATLDave]

Sure. I have no idea how much the slide itself will bounce, but that's the part we're concerned about, and even if it only bounces 20%, that still increases the impact velocity more than just the firing pin falling on its own.

Only if that bounce is timed to happen before the FP has reached the end of its downward motion. Otherwise it's chasing a retreating FP. Which is it? I don't know.

I remain skeptical that there's any discernable difference between the safe drop height of a hammer down and hammer up 1911.

 

[Vern Humphrey]

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.

Okay. What holds the pin in place for the primer to rise and be ignited?

The pin is held back by the firing pin spring. If the pin has no momentum, what keeps it in position firmly enough to dent the primer?

 

[RX-79G]

Vern,

I didn't say the pin doesn't have momentum. It does. And in the statement you quoted I was saying that the momentum of the pin alone wasn't sufficient to fire the primer, because we know of examples where it won't. I was saying that it takes both the momentum of the pin and the upwards momentum of the pistol to crush the primer.

Only if that bounce is timed to happen before the FP has reached the end of its downward motion. Otherwise it's chasing a retreating FP. Which is it? I don't know.

How is the pin going to rebound before the gun that it is inside?

 

[Vern Humphrey]

The Original Question was:

Inertial firing pins - less drop safe hammer cocked?

And the answer is, “No.” There is not enough momentum in the firing pin, as you say, to fire the gun on its own – and the tiny amount added by having the firing pin 0.1” or so higher at the start of the drop doesn’t change that.

 

[RX-79G]

Vern, I don't know how you are able to separate the velocity of the gun from the question of dropping a gun.

 

[FL-NC]

RX- regarding the Makarov vs the M16- you can't drop a M16 and have it land on the hammer.

 

[Walt Sherrill]

As I said earlier, I'm not good with physics, but...

If the firing pin doesn't have enough force/mass/inertia (or whatever term is appropriate) to ignite the primer before the bounce, why does it have sufficient force to do so after the bounce? The barrel is bouncing, but so is everything else!

Doesn't the same mechanism/force that makes the barrel and slide bounce also make the firing pin and firing pin spring bounce, too? And the firing pin spring, which was compressed by the original firing pin inertial movement (and by it's own inertia) will seemingly also be pushing the firing pin away from the barrel and the chambered round.

If the firing pin didn't have sufficient weight/mass/velocity, etc. to bridge the gap before the barrel bounce, why is that gap suddenly a non-issue? What is causing the firing pin to move in a different direction than the barrel and chambered round? Isn't that necessary for the gap between the breech face and primer to be bridged?

Someone familiar with the physics at play here (that some of us ) might have to explain... I understand that I'm struggling...

.

 

[RX-79G]

FL-NC

The Makarov has sturdy hammer intercept that keeps the hammer off the firing pin, like a SIG.

Are you saying the Mak hammer intercept is known to break under impact?

 

[RX-79G]

Walt,

Let's say it takes 13m/s of firing pin velocity relative to the primer for ignition.

And let's say that the firing pin, relative to the ground, is only going 10m/s when the muzzle hits.

If the gun bounces up, it is now moving the primer up toward the firing pin. Let's say it retained 40% of its energy from hitting the floor and is rising off the floor at 4m/s.

Like a head on collision, the downward moving 10m/s pin is going to strike the 4m/s upward moving gun and primer. 10+4=14m/s, which is 1m/s more than needed to pop the primer.

Before we get into why the firing pin position might matter, does that make sense that pin down + gun up = greater total ignition velocity?

 

[FL-NC]

The Makarovs we had, the hammer would "free float" 1/8" or more (guess) if the pistol was on FIRE, with the hammer down (decocked). We were told that if it was dropped in this condition and landed on the hammer that it could fire. Just reporting what the school says. There was nothing between the hammer and the firing pin tang. Never tested it, and other than the basics of familiarization, didn't work with them too much- most folks we worked with overseas had some type of western euro or American pistol. The few times I even dealt with Makarovs deployed, it was generally taking them from people who no longer needed them, clearing them, putting them in a bag.

 

[RX-79G]

I believe the 1/8" of float is because the hammer is a rebounding type. But it should be impossible to push the hammer into the firing pin with the trigger forward.

 

[JTQ]

RX-79G wrote,
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.

Lets suppose there is a theoretical drop safe advantage for a 1911 with the hammer down vs a 1911 with the hammer cocked. I don't know there is, lets just say there is for the sake of argument. I believe any safety advantage you'd gain in the rather unlikely situation of dropping your gun directly on the muzzle from a specific height where a discharge could occur, is outweighed by potential for an accidental discharge of lowering the hammer to put the 1911 into Condition 2.