Changing firing pin prutrusion as a way to gain a little effective pin fall?

B

Boyd Allen

Active member
In discussions of bolt action rifle ignition systems, it is the common practice to measure and discuss the distance that a firing pin falls, from its cocked position, to the point where the shoulder at the front of the pin stops it inside the bolt, BUT if when in this position the tip of the pin protrudes farther than a primer would allow, could we not gain some net, or real fall by shortening the tip?

My friend Bob Greenleaf tells me that he sets Savages for a .035 firing pin protrusion with no problems, yet the common specification is more like .055. While I realize that for factory actions, with their relatively generous pin falls, this sort of change may not have any effect, perhaps for some benchrest actions that have pin falls that are nearer the edge by design, and which may be unintentionally taken over the edge by variations of triggers, or for which the original design was marginal, could not a modification be potentially beneficial? Have any of you played with this?

Because of the relationship of acceleration (progressively increasing speed) and momentum, or energy for that matter, it would seem that changes in fall would have more of an effect than their percentage of of the total fall would seem to indicate.
 
I have no answer, but, to extend the hypothesis, would either tip length be more resistant to blanking?
 
If their shapes were the same, I wouldn't think that there would be a difference, but maybe I don't properly understand your question.
 
I've shortened the firing pin fall on my live varmint rifles after reading Mr Greenleaf's articles on the subject in PS using shim stock on the actions that don't allow adjusting protrusion without machine work, and by adjusting the protrusion on my two Savages. No problems with ignition or changes in accuracy that I can tell, but with my eyesight going south that's sometimes hard to tell. As close as I can measure the firing pin protrusion on all those actions is 0.035".

Most modern factory sporting rifle actions have about 1/4" firing pin fall, which with the firing pin springs used seems to do the job. I'm not sure that custom actions have much shorter firing pin falls, but sure wouldn't put any money on that.
 
Even if you have .050 to .060" firing pin protrusion when measured with the firing pin in the fired position doesn't mean that you still do when it hits a primer. I haven't ever measured the dent in a fired primer but don't think it's anywhere near .050 to .060".
 
Mike,
I think that the depth of the dent that the pin tip makes in a primer my be decreased by the peak pressure of the load. It might be interesting to compare the depth of the dent in a primer that was fired in an empty case to one that was part of a warm to hot load.
Boyd
 
Mike Bryant said:
Even if you have .050 to .060" firing pin protrusion when measured with the firing pin in the fired position doesn't mean that you still do when it hits a primer. I haven't ever measured the dent in a fired primer but don't think it's anywhere near .050 to .060".
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Mike, according to Greg Walley, the firing pin, from rest against a live primer in a case that is firmly against the bolt face, then after that firing pin falls on a normal firing cycle, the difference should be 0.020".

NOTE-do this outdoors with the muzzle pointed in a safe direction ON A PIECE OF BRASS THAT DOES NOT CONTAIN POWDER OR BULLET!!!

To do this test, just decap a case that was fired in that exact chamber (do not resize the case). This assures the case is firmly seated in the chamber and firmly against the bolt face.
 
I am not sure about this and how it might interact but the carbide primer pocket uniformers I have are not the same depth of cut from one to another. Thus moving the primer further away from the bolt face.
Centerfire
 
Mike Bryant said:
Even if you have .050 to .060" firing pin protrusion when measured with the firing pin in the fired position doesn't mean that you still do when it hits a primer. I haven't ever measured the dent in a fired primer but don't think it's anywhere near .050 to .060".
Click to expand...

You ass-u-me the dimple is the same after the cartridge fires as it is when the firing pin falls. Don't forget that the primer receives a great deal of flattening force in the process of ignition. Internal and external force. No primer in ANY rifle is going to show a dimple anywhere near what the actual firing pin made. basic physics.
 
David,
Do you think that the primer itself would push the dent back out, or would it take the pressure of an ordinary load? I am thinking that if I take an old and ugly fire formed case, and drill out the flash hole as large as possible while still leaving enough lip for the feet of the anvil to rest on, and just fire the primer, that we might be able to get a real measurement, without any push back. What do you think?
Boyd
 
The best thing I found for killing primers was soaking in a strong solvent (MEK, acetone etc) .....experiment until you find one that takes the shine off the priming compound.

Some solvents though I soaked some primer brands for DAYS and k'BOOM!

al
 
I have fired a primer only a number of times safely into the toilet bowl in my bathroom :). Don't have to worry about starting a fire and while ther isn't much sound involved, it is reduced somewhat. Really, it isn't any less safe than one's gas grill puffing from a bit too much gas accumulation
 
Boyd Allen said:
David,
Do you think that the primer itself would push the dent back out, or would it take the pressure of an ordinary load? I am thinking that if I take an old and ugly fire formed case, and drill out the flash hole as large as possible while still leaving enough lip for the feet of the anvil to rest on, and just fire the primer, that we might be able to get a real measurement, without any push back. What do you think?
Boyd
Click to expand...
bOYD,

Boyd, I think your premise is valid, for PRIMER ONLY. But simply dropping the firing pin in the bolt will give you a measurable distance of protrusion. Not fall, just final protrusion.
 
I guess that what I am getting at is that if the pin has some amount of its total fall, on an empty chamber, that is not being used in a normal firing that reducing the protrusion might put some of this unused fall to work, while at the same time avoiding having the shoulder of the pin of cocking piece strike the bold body during firing, and increasing the energy and momentum delivered to the primer. Of course the desirability of this increase would depend on what you were starting with. There are some actions that are right on the border of enough, while others probably have more than enough, and which might actually benefit from a reduction. Some of the newer benchrest designs have about .200 pin fall, with a trigger that has a proper top lever (sear?) configuration, and if the trigger is not correct in this respect then there may be too little. I believe that this is the reason for the proliferation of trigger hanger options being offered by some action manufacturers. For something like a Panda, or a sleeved Remington, I doubt that there is an issue with having enough pin fall.

A while back, Jerry Stiller posted that he is of the opinion that increasing spring weight and striker fall may not eliminate the need for sufficient pin fall. This started my thought process as to how some net fall might be gained.
 
my question is should i measure fireing pin fall or travel on a empty chamber or with a fired case ?
I have been playing with one of my action's , working on cocking cam,pin shroud ect trying to make it work alittle better, debured and polished my trigger up. i feel i may have had some inconsistant ignition.. i'm measueing my pin fall on a empty chamber at @ .215 and been thinking about increasing it to .225 or so.
 
I think that most of the numbers that are tossed around in discussions are fall on an empty chamber. What I am/was talking about in the first post of this thread is the distance from cocked to stopped by the primer, before any blow back (reduction of primer dent depth caused by peak load pressure). I would assume that there would need to be some gap at the front of the firing pin shoulder, and that similarly there should be some between the front of the cocking piece and the bottom of the cocking cam notch, but if we can let the pin fall farther by shortening the tip of the pin by say .015, then we get a little more energy, at the same spring rate, and as long as all we are doing is narrowing the gap between the front of the pin shoulder and the inside of the bolt, without it touching while firing a loaded round, that looks like a free gain, if a gain is what one is looking for.
 
boyd i do understand what you are saying completely..but my question is how much pin fall or travel do we really need? how is it measured ? so decreaseing the pin protrusion could gain pin fall giving it more energy..but how do we know if we need more ?

oh and the action i'm playing with is not my Borden action,,I just shoot it and clean it..lol
 
I think that that will only be determined experimentally. Short answer, I don't know. What I do know is that there seems to be a multi-gunsmith cottage industry engaged in modifying a popular action that is perhaps near the edge on energy. Actually, I am just guessing here, but I think that this is one of those areas where differences are supposed to become visible if everything else is perfect, and the shooter is at a high level of skill....which means that I probably shouldn't be loosing much sleep. Nevertheless, theory is fun, as is figuring out work-arounds. My Viper came with a total fall of about .200, and a spring that weighed about 19#. The nominal firing pin tip diameter is .062, which is supposed to reduce the energy requirement because the force is concentrated in a small area ( I think). It shot fine that way, but not being content to leave well enough alone, on the advice of someone who really should know, I reversed the trigger hanger, gaining .020 in pin fall, to a total of .220. It still shoots fine. I tried a light pin, that has a fluted aluminum shaft, and requires (according to the manufacturer) a 25# spring. This reduced the momentum to about 60% of stock, while keeping the kinetic energy about the same. It seemed to me that there was less cross hair jump, dry firing on an empty chamber with this configuration, almost none with a cushier rear bag. Recently, after hearing about some smiths adding weight to the pin assembly, I have been trying the stock pin, with the 25# spring. It seems to work fine, but I think that I will give the light pin a try again. None of these configurations have shot badly, and judging any difference shooting at an outdoor range is subjective to say the least. These changes have been made over a relatively long time, and none have succeeded in compensating for mediocre tune or errors in reading flags. My best guess is that there is a range in which differences in fall will not show up on the target, and that as long as you are within it you are good to go.
 
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boyd looking in Boyer's book, page 58 i found my answers..removed my bolt (custom action) and my fireing pin protrusion is .055. my pin rest on the spring holder bevel..so decreasing my pin tip would only decrease the pin tip..it also looks to me in order to get a real accurate read on pin travel(fall) you would have to have the barrel off and trigger installed fireing pin in the fired position and somehow measure it in that position to be sure the trigger was not holding it up any..so it looks to me to be real trickey to do it and be sure it's all working together properly. looks to me that the pin fall is from the cocked position to the total pin protrusion..so i would say decreaseing pin protrusion would not be gaining but decreaseing pin fall...
 
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