Firing Pin effect on ignition

JerrySharrett said:
The tip shape, generally accepted to be spherical is probably a minor factor, IMO.

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I agree, Jerry. But a smooth, spherical tip is likely to be less stressful on the primer cup. A sharp or rough tip is more likely to end up with a blanked primer...Not pierced, mind you. :D
 
mwezell said:
I agree, Jerry. But a smooth, spherical tip is likely to be less stressful on the primer cup. A sharp or rough tip is more likely to end up with a blanked primer...Not pierced, mind you. :D
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Oh I'm sure there could be tip designs that would puncture the primer. Someone in a book I read from discussed tip design and IIRC spherical was not the optimum.

(Remember, primers are never pierced!)

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JerrySharrett said:
Oh I'm sure there could be tip designs that would puncture the primer. Someone in a book I read from discussed tip design and IIRC spherical was not the optimum.

(Remember, primers are never pierced!)

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May well be....I do remember an unnamed but well respected custom action maker using a flat tip. It was clear to the eye and plain as day on a fired primer. I can't say with certainty that it mattered but I also can't imagine how or why it would help. Good ignition, in my feeble mind anyway, is much like breaking a piece of glass. Other than the stress put on the cup, I can't see how a tip that isn't smooth and round would be of benefit. Primer compound should be quickly "shattered", for lack of a better term, for best ignition...fast like striking a match.

I use the match analogy after talking with Allan Hall about RF ignition. He claimed that a hard, fast, but shallow hit of only .002" depth was sufficient for good ignition. I understand there are differences between rf and cf, but the priming compound is similar.

For this reason, my problem with the op's post is not as much about fp protrusion as it is about total energy with that amount of fall and spring energy/fp weight.
 
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I just got out a factory Remington firing pin and examined it with good light, in front of a white background, using my low power binocular magnifier. The tip appeared to be spherical, but you could see it turn the corner where it transitions to the cylindrical part. I think that this means that the radius of of the sphere is greater than that of the cylinder behind it. IMO this is to reduce the incidence of cratering because the hole if fully filled at slightly less protrusion.
 
Boyd Allen said:
I just got out a factory Remington firing pin and examined it with good light, in front of a white background, using my low power binocular magnifier. The tip appeared to be spherical, but you could see it turn the corner where it transitions to the cylindrical part. I think that this means that the radius of of the sphere is greater than that of the cylinder behind it. IMO this is to reduce the incidence of cratering because the hole if fully filled at slightly less protrusion.
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Mathematically speaking what you see is a truncated sphere or a spherical cap as opposed to a hemisphere.


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More firing pin minutia:

In geometry, a spherical cap or spherical dome is a portion of a sphere cut off by a plane. If the plane passes through the center of the sphere, so that the height of the cap is equal to the radius of the sphere, the spherical cap is called a hemisphere.

So it seems that under the above stated conditions a "spherical cap" can also be a "hemisphere".
 
WSnyder said:
More firing pin minutia:

In geometry, a spherical cap or spherical dome is a portion of a sphere cut off by a plane. If the plane passes through the center of the sphere, so that the height of the cap is equal to the radius of the sphere, the spherical cap is called a hemisphere.

So it seems that under the above stated conditions a "spherical cap" can also be a "hemisphere".
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Certainly would be if the altitude of the cap is the same as the radius of the sphere. Redundantly we say!!!


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JerrySharrett said:
Oh I'm sure there could be tip designs that would puncture the primer. Someone in a book I read from discussed tip design and IIRC spherical was not the optimum.

(Remember, primers are never pierced!)

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from our archives......

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Mike Bryant

11-08-2010, 07:59 PM

A blanked primer is the "technical" or correct name for a pierced primer. The cartridge fires with too high pressure resulting in a hole in the primer. Gas shoots out the hole in the primer, blowing the small disk that came out of the primer back through the firing pin hole. The gas then blows the cocking piece back farther than it should and then the firing pin spring drives the cocking piece forward hitting the top bar on the trigger. You might get by with it once, twice or more times, but more than likely it's going to break something in the trigger eventually. The cocking piece driving forward has the same effect as hitting the trigger with a small hammer. I've seen the top bar and a few other of the levers inside Jewell trigger break all caused by blanked primers.
 
Holes in Primers

from 6 br forums........


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Holes in my primers
« on: 10:20 AM, 06/15/12 »
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Ok, pretty sure I know the answer, but here goes. 30 BR @ 34.2 gr. of 4198. I use Rem brass for my 30 BR repeater and use it for Yotes. I think, the large hole in the primer pocket is the cause for holes in the primers. It doesn't do it when using the same load in my other 30 BR for benchrest. Same Barrel (Kreiger), same gunsmith (DD), same reciever, same chamber (.330), different brass (Lapua) with small primer holes. The only difference is the brass. It shoost very well, just pokes holes in the primer. This reciever was a 22-250 prior to a 30 BR. Do you think the firing pin difference between large and small primer is the culprit, or the size of the hole in the primer pocket? Do you think Mag primers will solve the problem? It pokes holes in the primers with CCI, Wolf, and Tula SR primers.

Tom
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Blanking Definition

Hoping this will solve some misunderstanding of what the term "blanking" actually means.... and I believe the word is taken from tool and die work and applied to us shooters.....of whom many are tool and die/machinists....

Blanking: A blanking die produces a flat piece of material by cutting the desired shape in one operation. The finish part is referred to as a blank. Generally a blanking die may only cut the outside contour of a part, often used for parts with no internal features.
Three benefits to die blanking are:
Accuracy. A properly sharpened die, with the correct amount of clearance between the punch and die, will produce a part that holds close dimensional tolerances in relationship to the parts edges.
Appearance. Since the part is blanked in one operation, the finish edges of the part produces a uniform appearance as opposed to varying degrees of burnishing from multiple operations.
Flatness. Due to the even compression of the blanking process, the end result is a flat part that may retain a specific level of flatness for additional manufacturing operations.
 
It is quite common for pressure behind that blanked disk to push the firing pin back far enough for the blank to end up inside the bolt and stop the firing pin from ignighting the next shot. Many times I have taken my bolt disassembly tool to the bench when I had loads that were really hot.

Having standard 0.078" pins reduced to 0.068" or 0.062" is common. Greg Tannel keeps busy doing that. Hard to blow a primer with a 0.062" pin.....but I have!



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JerrySharrett said:
It is quite common for pressure behind that blanked disk to push the firing pin back far enough for the blank to end up inside the bolt and stop the firing pin from ignighting the next shot. Many times I have taken my bolt disassembly tool to the bench when I had loads that were really hot.

Having standard 0.078" pins reduced to 0.068" or 0.062" is common. Greg Tannel keeps busy doing that. Hard to blow a primer with a 0.062" pin.....but I have!



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Not hard at all, Jerry. Put your .062 pin in a bolt with a fp hole for a .078 pin and you'll see how easy it is.:p
 
It is my impression that when one gets a round hole in a fired primer that is about the size of the pin hole in the bolt face, that what has happened is that the pressure on the front side of the primer became great enough to overcome the inertia of the striker assembly and the force of the spring, and back the pin up far enough so that the primer was pushed into the pin hole, shearing the cup material. Heavier springs, and firing pins help mitigate this, as do smaller diameter firing pins. The reason for the latter is that the amount of pressure exerted on the firing pin tip is its cross sectional area multiplied by the pressure in pounds per square inch. If we pick .072 and .062 as our tip diameters, a little calculation will show that the area of the larger one is about 1/3 greater than the smaller, or putting it another way, the smaller 75% of the larger. These percentages also show the difference in pin "backup force" at a given chamber pressure.

Perhaps 30 years ago, I made a reloading error that opened up the primer pocket of an '06 case to the point where the primer fell out when the bolt was opened. The pocket looked like it would take a shotgun primer. The rifle was a Springfield with a double heat treat receiver, and a Remington bolt ( a parts gun shooter) The firing pin spring had been replaced with the heaviest one that two strong hands could assemble onto the two piece pin, and the pin hole in the bolt face was a good fit on the pin, and had a sharp corner. As you may know the striker weight of those rifles is among the highest, as is the pin fall. Curious, I examined the primer, it had a perfectly formed indentation, and no sign of a crater.

I have seen several kinds of primer failure. I have seen them crack (which I thought to be the result of a cup material problem), which flame cut the firing pin tip, and sharply increased the number of similar problems after that, until the cut tip was fixed. I have see the so called blanking mentioned above, and I have seen leaks around the perimeters of primers that pitted bolt faces. Then there have been reloader failures that resulted in problems in the area of the primer, like the example with the Springfield.
 
The reasoning for using the truncated sphere or cap as opposed to the full hemisphere is to eliminate the wedging effect of where the full hemisphere approaches the vertical (cylindrical) surface of the firing pin body.

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Something I don't understand

I was shooting a fairly hot load at the nationals and was doing pretty good - good enough not to change anything. Every now and then I'd have a hole in the primer and didn't think much of it as, again, I was shooting pretty darn good. I looked at my bolt face and realized that the firing pin hole was plugged with a piece of primer so I took it apart to clean it. Turns out, there was a whole bunch of pieces all about - two or three in the firing pin hole. I cleaned the pieces out and proceeded to shoot poorly for the remainder of the nationals. I've often wondered what actually happened there!! Well, I say often, but I've tried to block that incident out as much as possible.
 
Wilbur said:
I was shooting a fairly hot load at the nationals and was doing pretty good - good enough not to change anything. Every now and then I'd have a hole in the primer and didn't think much of it as, again, I was shooting pretty darn good. I looked at my bolt face and realized that the firing pin hole was plugged with a piece of primer so I took it apart to clean it. Turns out, there was a whole bunch of pieces all about - two or three in the firing pin hole. I cleaned the pieces out and proceeded to shoot poorly for the remainder of the nationals. I've often wondered what actually happened there!! Well, I say often, but I've tried to block that incident out as much as possible.
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What happened? you molested some primers.

You did not puncture them, never happens.

Still looking for HFV a pup.

Can unhousetrained pups ride in your Cadillac?


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Wilbur You were Lucky, My buddy pierced a primer with his 6 Dasher. We were wondering why the rest did not have any pressure signs, He ended up winning his relay but in the shoot off the thing wouldn't fire, I was in the pits so I didn't see what happened. Took the bolt apart and sure enough piece of the primer. So I'd say if that happens take the bolt apart and clean it.

Joe Salt
 
Pierced primer pic......

Click on my previous post pic........to see......VERY small hole.

Kevin
Is this any better?
6gzq6b.jpg
 
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