What does it take to set off a primer?

keys85 · February 3, 2009, 11:55 PM

For the sake of accidents, we'll say a sensitive primer. I read somewhere it was around 12 ft/lbs of force? I can't remember. Does anyone know? I may be mistaken and that could be for rimfire.

Furthermore, does it take a certain amount of depth of the firing pin to contact the primer to cause ignition?

I'm trying to figure the likelihood of having a slam fire on my CZ-52. I already know about decocker problems and poor design. I will also add that the internet says a lot about worn decocker notches, thus meaning, while dropping the hammer having the safety swing back to the fire position, allowing the hammer to fall further and kiss the firing pin. By design, having the decocker deactivate the firing pin block for any motion of the hammer is stupid anyways. Needless to say, I think the dimensions of the firing pin and firing pin block and how well they mate is more crucial to whether an AD may occur than anything else.

With my firing pin fully forward in the slide, it protrudes from the breech face anywhere from .001 to .003, it's impossible to measure, and hard to tell but I know it's there. When I look at my chambered rounds, they have dings on them. Granted a sensitive, raised primer may come along some day, what are my chances of having a slam firing by having the firing pin strike a primer with only a depth of say .002" at nominal velocity of dropping the slide (or better, from me dropping the pistol from waist height?)

Should I worry and ride the slide with this old war horse, or should I grind off a few thousandths off the firing pin?

**Unclenick** · February 4, 2009, 12:21 AM

I don't know how many foot-lbs/in² (energy per unit firing pin tip area) are required? It varies by brand owning to differences in priming mix and primer cup hardness. I do know that slam fires occur when the inertia of bolt closing causes the firing pin to coast forward into the primer with enough force to fire it. This requires two things: very fast bolt closing (the slam) and a firing pin that floats (has no return spring to keep it from coasting forward). This is a problem in semi-automatic military rifles which meet both conditions, though it isn't a frequent event. Bolt action rifles don't meet either condition if they've been put together with all their parts. When a bolt action fires on closing the bolt, that is an actual firing, releasing the cocked striker. It is due to a faulty trigger or cocking mechanism and none of the steps you take with ammunition to prevent slam fires will have any effect on it. Handgun firing pins all have return springs, AFAIK, and don't float forward, at least, not very far or with very much force owing to the springs. Handgun strikers will be held back same as the bolt action.

In the case of handguns or bolt action rifles, it is usually the trigger mechanism that is to blame for firing on closing. High primers can also cause an issue. Ideally the primer should be about three to five thousandths below flush with the back of the casehead.

jmorris · February 4, 2009, 10:10 AM

In very limited cases a 9 volt battery does the trick. Back in the mid 80’s Beeman imported Krico rifles that set off regular primers electronically. Both rimfire and center fire versions were made. Krico only made a few before going back to conventional rifles. They offered the technology to REMINGTON, ANSCHÜTZ, WALTHER and a few others but no one picked it up. Remington came out with an electronic firing rifle of its own design, but it tanked because it used “special” primers.

February 3, 2009, 11:55 PM	#1
keys85 Junior member Join Date: September 20, 2008 Posts: 199	What does it take to set off a primer? For the sake of accidents, we'll say a sensitive primer. I read somewhere it was around 12 ft/lbs of force? I can't remember. Does anyone know? I may be mistaken and that could be for rimfire. Furthermore, does it take a certain amount of depth of the firing pin to contact the primer to cause ignition? I'm trying to figure the likelihood of having a slam fire on my CZ-52. I already know about decocker problems and poor design. I will also add that the internet says a lot about worn decocker notches, thus meaning, while dropping the hammer having the safety swing back to the fire position, allowing the hammer to fall further and kiss the firing pin. By design, having the decocker deactivate the firing pin block for any motion of the hammer is stupid anyways. Needless to say, I think the dimensions of the firing pin and firing pin block and how well they mate is more crucial to whether an AD may occur than anything else. With my firing pin fully forward in the slide, it protrudes from the breech face anywhere from .001 to .003, it's impossible to measure, and hard to tell but I know it's there. When I look at my chambered rounds, they have dings on them. Granted a sensitive, raised primer may come along some day, what are my chances of having a slam firing by having the firing pin strike a primer with only a depth of say .002" at nominal velocity of dropping the slide (or better, from me dropping the pistol from waist height?) Should I worry and ride the slide with this old war horse, or should I grind off a few thousandths off the firing pin?

February 4, 2009, 12:21 AM	#2
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	I don't know how many foot-lbs/in² (energy per unit firing pin tip area) are required? It varies by brand owning to differences in priming mix and primer cup hardness. I do know that slam fires occur when the inertia of bolt closing causes the firing pin to coast forward into the primer with enough force to fire it. This requires two things: very fast bolt closing (the slam) and a firing pin that floats (has no return spring to keep it from coasting forward). This is a problem in semi-automatic military rifles which meet both conditions, though it isn't a frequent event. Bolt action rifles don't meet either condition if they've been put together with all their parts. When a bolt action fires on closing the bolt, that is an actual firing, releasing the cocked striker. It is due to a faulty trigger or cocking mechanism and none of the steps you take with ammunition to prevent slam fires will have any effect on it. Handgun firing pins all have return springs, AFAIK, and don't float forward, at least, not very far or with very much force owing to the springs. Handgun strikers will be held back same as the bolt action. In the case of handguns or bolt action rifles, it is usually the trigger mechanism that is to blame for firing on closing. High primers can also cause an issue. Ideally the primer should be about three to five thousandths below flush with the back of the casehead. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle Last edited by Unclenick; February 4, 2009 at 12:34 AM.

February 4, 2009, 10:10 AM	#3
jmorris Senior Member Join Date: November 22, 2006 Posts: 3,077	In very limited cases a 9 volt battery does the trick. Back in the mid 80’s Beeman imported Krico rifles that set off regular primers electronically. Both rimfire and center fire versions were made. Krico only made a few before going back to conventional rifles. They offered the technology to REMINGTON, ANSCHÜTZ, WALTHER and a few others but no one picked it up. Remington came out with an electronic firing rifle of its own design, but it tanked because it used “special” primers.