Firing pin force

[davlandrum]

Sorry if this is slightly off the wall, but one of my students in Hunter Ed asked me and I did not know, but told him I would see if I could get an answer.

How much force from a firing pin is required to detonate the primer?

[wogpotter]

It will depend on the primer somewhat.
Pistol primers, rifle primers, and magnum primers have differing cup material so this will need more force to crush against the anvil to ignite the priming material.
There's also the fact that the total pressure exerted by the hammer & spring are multiplied a lot by the tapered tip of the firing pin. This makes a "10 pounds" type of answer not very accurate.

You could do a test, but it would take quite a lot of work & you'd need to take safety precautions as you'd be igniting a primer.

I guess the best answer is "enough force imparted by the hammer & spring to crush the priming pellet between the depressed part of the cap & the internal anvil.
You could get a basic idea by using a spring gage to pull the firing mechanism back from uncocked, but that won't acount for the differences in primers.
*edited to add a bit of info*
I just did the pull the striker back test on 2 rifles I own.
One was 28Lbs, the other 17Lbs.
The 28Lb one was a bolt action, and the other the hammer on a semi-auto. I guess it's not that consistent a thing?

[Scorch]

It will depend
I guess
You could get a basic idea
Rather than guess, why not ask? Here is the "Contact Us" page from the CCI web site, try calling them.
http://www.cci-ammunition.com/about_us/contact.aspx

[Brian Pfleuger]

I've heard that a firing pin is supposed to produce enough force to launch a pencil 3 feet straight up. (I think it was 3 feet)

[kyle1974]

force is just the mass x acceleration...

take your firing pin out and weigh it... then get a radar gun and clock the speed that it impacts the primer at.... VOILA! you have you answer!:D

[Brian Pfleuger]

force is just the mass x acceleration...

Actually, since you're measuring speed not acceleration, the equation you're looking for is either momentum or kinetic energy:

p=MV or ke=1/2MV^2


Not that any of the 3 would actually be helpful in this situation.:D;):rolleyes:

[davlandrum]

Glad I am not the only one who did not know an answer off-hand.:D

I'll get right on that radar gun thing....

Wog - thanks for the effort!

[Yithian]

Each manufacturer is different.
Remember the craze where soft primers were causing doubles (CCI)? People were worried that the soft primers were going to get them arrested if an ATF guy was at the range.

Some manufacturers even have "special" primers for floating firing pins (ie. AR-15's)(again CCI). They are harder than their normal primers, literally.

It wouldn't be too hard for an intelligent redneck to discover the speed and pressure required to set off a specific primer, but what is the point?
The main primer ingredient is nitroglycerin. Apply slow pressure and it won't detonate. And, it is surprising how little pressure can QUICKLY set it off.
The math is in how hard the cup is.
Dent it with incremental weights, then apply speed to the dent. Bang.
Do the math on surface area of the firing pin face vs one inch and : answer in Lbs/sq inch. (for that specific lot of primers)

I'm sure there is a notation available in mathematics for mass and velocity. Someone here will chime in and fill the gap.

[kraigwy]

Most reloading manuels tell us the make up of primers so I wont list them here.

However nitroglycerin, isnt one of the ingredients.

[Slamfire]

The answer is not clear cut. Primers are made from chemicals. The activation energy varies. Some primers, within the same lot, are more sensitive than others. Its going to follow a statistical curve, but I don't know the distribution. Maybe somthing similiar to a upside down bath tub curve.

The book "Ammunition Making" by George Frost has a section on primer testing. (Incidentally now that these books are $115.00 used, I can't find mine :mad:) Primers are tested for lot sensitivity by dropping steel balls on them.


Winchester was helpful in reading to me the industry specification requirement for primer sensitivity for the 308- 30-06 cartridges. Unfortunately Winchester was unable to tell me what the specification number was, just to contact SAMMI to get the specification. Industry organizations do not release their specifications for free, and so I remain ignorant of the spec. And since the following is per a telephone conversation, there may be errors in the transcription:

Drop Height of 4 oz ball

no misfire no explosion no failure to fire no failure to fire
Any case 100 cases 200 cases all cases

308 Primed case 3” 4.5” 22” 25”

30-06 primed case 3” 4.5” 22” 25”


Mil-P-46610E “Primers, Percussion for Small Arms Ammunition” was the actual military specification for primers. Was until the Clinton/Gore administration “retired” all military specifications. Without creating alternatives. But that is another story. The following section is from Mil-P-46610E:



3.2 Sensitivity.-The sensitivity shall fall within the limits specified as follows for each type of primer:


Primer Required Case Height in Inches
H +5S H -2S
Dwg . No. B10522621 7.62mm Match 15 3
Dwg . No. B10535489 7.62mm Match 16 3
Dwg , No. B10522621 7.62mm 15 3
Dwg . No. B8594094 7.62mm Match 16 3
Dwg. No. B10522621 7.62mn Grenade 15 3
Dwg . No. B10522621 7.62mm Blank 15 3
Dwg . No. B10535489 7.62mm Blank -Caliber 16 ½ 2½
Dwg . No. B10522621 .30 15 3
Dwg. No. B10535489 Caliber .30 15 2½
Dug. No. A5000131 Caliber .30 15 2½
Dug. No. B8595819 Caliber .30 Match 15 2½
Dwg, No. B10535489 Caliber .30 Match 15 2½
Dwg. No. C7645332 Caliber .30 Blank 15 2½
Dwg. No. B8594094 Caliber .30 Blank 15 2½
Dwg. No. B6200959 Caliber .30 Carbine 18 2½
Dwg. No. C11751131 Caliber .30 Carbine 18 2½
Dwg. No. B7645336 Caliber .45 16 2½
Dwg. No, A5001168 Caliber .45 16 2½
Dwg. No. B7645339 Caliber .50 15 2½
Dwg. No. A5033178 Caliber .50 15 2½
Dwg. NO. B7645336 Caliber .45 Blank 18 3
Dwg. No. A5001168 Caliber .45 Blank 18 3


4.4 Test methods and procedures.

4.4.1 Sensitivity test.-Ambient temperature - The primer shall be inserted into the primer pocket of the cartridge case so that the surface of the primer cup, when measured from the center of the primer, is within the tolerance specified on the applicable cartridge drawing. The test shall be performed in accordance with the complete run-down method described in TECP 700-700, Vol. III: AMCR 715-505, Volumes 3 and 5; or AMSMU-P-715-501FAI as applicable.

4.4.1.1 Two-height method.-The two-height method of testing for sensitivity may be used in lieu of the complete run-down test when sensitivity results for five consecutive lots have been found to comply with the requirements of 3.2 and computed skewness values have been found to be no greater than .787 nor less than -.787 (see 603). However, one out of every 10 lots submitted shall be tested by the complete run-down method. Failure in any test to meet sensitivity or skewness requirements shall be considered sufficient cause to revert to use of the run-down method on each lot. The two-height test shall be conducted in accordance with the two-height method described in AMSMU-P-715-501FA1 Fifty primers shall be tested at each height.


As to calculating firing pin energy, Volume one of "The Bolt Action" by Stuart Ottenson has an appendix.

[TheManHimself]

The main primer ingredient is nitroglycerin.

Incorrect. Nitroglycerin is a component in double- and triple-base gunpowders, but not in primers. Lead azide and perchlorate compounds are used in primers.

[wogpotter]

Thank you, Slamfire. Much more detailed explaination.

[dbooksta]

The problem is that primer detonation depends on both force and "shock." A well-known demonstration is to slowly crush a primer in a bench vise (it won't detonate), and then hit the vise with a hammer. The shock created by the hammer blow will usually detonate the primer compound.

After years of getting occasional failures to detonate from match-grade AR-15 triggers even on FGM match primers I finished a study in which I looked at both peak instantaneous hammer force and total hammer energy. Of course, given the design constraints on an AR-15 trigger the two are related: Peak force ranges from about 20 pounds on the most reliable triggers (mil standard or Hiperfire) to as low as 12 pounds (e.g., Timney's 3-pound drop-in trigger). Energy transmitted through the firing pin ranges from 18 inch-ounces on a mil-standard trigger to as low as 10 inch-ounces on the Timney. At the low end, notoriously hard primers often fail to detonate, and even thin-cupped primers will occasionally fail.

[JoeSixpack]

Book, You make a good point.

Still.. Like Brian said you can pencil test the gun.. Now I've never done a rifle, they're generally harder to test because most rifles are to small for a pencil to fit.

Handguns are easier.. He said 3ft, I don't know exactly what right amount is but most Guns will easily do more then that so it's probably a good rule of thumb 3-4 feet.

It's also a good way to field test a gun before buying.

[hdwhit]

kyle 1974 wrote:
force is just the mass x acceleration...

take your firing pin out and weigh it... then get a radar gun and clock the speed that it impacts the primer at.... VOILA! you have you answer!


No.

The engineering term for Speed is Velocity.

Acceleration is the rate of change in Velocity.

So, measuring the speed of the firing pin at the point it strikes the primer (assuming you could even get access to make this observation) would give you its Velocity at the time it struck the firing pin, not its Acceleration.

Mass * Velocity = Momentum (Not Energy)

In the absence of Acceleration, Energy at any instantaneous point in time is:

Energy = 1/2 * Mass * Velocity * Velocity (i.e. Velocity squared).

But none of this would answer the OP's question since the Energy needed to crush a primer is irrelevant to its ignition. You can put a primers in a vice and slowly crush it into a pancake without it igniting. The key to igniting a primer is not simply applying Energy, but applying sufficient Energy over a short enough period of time to generate the shock necessary to ignite the primer mixture.

[hdwhit]

TheManHimself wrote:
Lead azide and perchlorate compounds are used in primers.


Modern primers use lead styphnate.

Lead azide and perchlorate were used in corrosive priming mixtures which have largely been supplanted worldwide.

[hdwhit]

davlandrum wrote:
How much force from a firing pin is required to detonate the primer?


Detonation of a primer requires a sufficiently energetic force applied over a small amount of time to generate the "shock" necessary to ignite the lead styphnate high explosive priming compound.

Technically, this "shock" would be a "jerk" (i.e. change in acceleration or second derivative of velocity) or even a "jounce" (i.e. change in jerk or third derivative of velocity) and I'm not aware of any published source for those figures.

[T. O'Heir]

OP is 8 years old. And firing pins have no force of any kind. The hammer/main spring does.