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Floating firing pin measurement


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#1 Steve McKuhen

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Posted 21 December 2011 - 02:11 PM

We need a way to measure the pressure of the strike of the floating firing pin as it hits the rim. This way we will know what combination works best. Roller's idea decreased the torque but did it change the striking force? How much force is needed to fire the rim fired 22? I did a short Google search this morning but could not find what I was looking for.
I am going to set up a jig using the scale I have and test several different springs.

If the shape of the head of the floating firing pin and the hammer were a ball or a semi circle the force would be concentrated on one point. This might decrease the strength of the spring needed?
I will make a pin with round balls and test it also.

#2 Roller

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Posted 21 December 2011 - 07:25 PM

Steve,

I calculated with my current set up that I am using 3.095 pounds to fire.

Frank

#3 Sparky_NY

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Posted 21 December 2011 - 10:48 PM

The force that the pin hits with is only part of the deal. Most important is the shape of the end of the pin. The proper shape is that of a tapered wedge, sort of like a exclamation point, wider at the case rim and tapering towards the center. Proper shape also calls for the striking edge to be tapered also, so that it hits the rim first. There is info on the web about proper rimfire firing pin geometry, I read it in depth when I built a custom ruger 10-22 rifle.

The force driving the pin forward needs to be much less with a proper shape pin. Round flat pins or somewhat sharpened round pins are far from correct and would take much more force. Think in terms of lbs per sq inch, if the lbs is constant (spring rate) then the smaller area pin does indeed deliver a harder blow. Again, shape of the pin is most important also.

Just google "rimfire firing pin shape" and there is plenty to read/learn

Also, force required to detonate can vary a lot from brand to brand of ammo, the same for centerfire primers.

#4 Steve McKuhen

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Posted 03 January 2012 - 06:55 PM

This is my attempt to measure striking pressure so I would have a way to compare the springs, friction, ect. I used an old cocking ring as a trigger. It did not work. The scale seems to have some protection as it will not show a strike. Need to find a different scale, gague. Any suggestions?

 

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#5 Roller

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Posted 03 January 2012 - 07:42 PM

Neat idea Steve! How about using one of those devices to measure impact. I don't know what they are called but I have read about them being put in a package to record impacts received during shipping.

Frank

#6 shred

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Posted 05 January 2012 - 03:22 AM

The lag time on that scale is unlikely to ever record impacts well. I'd try making a simple ballistic pendulum and see how that does.

#7 Pmercer

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Posted 05 January 2012 - 02:31 PM

I seem to recall about 18 years ago I was shown a device where a ball bearing was placed on a material and struck by a known weight. The ball bearing would dent the material and depending on the size of the dent, the hardness of the material could be established.
Could this same method be used to establish force??

As far as working out how much force is needed to set off a .22 round, how about pull the head and powder off of a live round and place it in a jig pointing downwards. By positioning and dropping a known weight onto a firing pin which is positioned over the rim, the force can be worked out.

Food for thought....

#8 Steve McKuhen

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Posted 05 January 2012 - 03:57 PM

What I am trying to do is to find an easy way to compare different springs and modifications to the bolt to each other to find the best combination with the least amount of pressure.
Such as the torque wrench idea that Roller has.
And to find out how much pressure is needed to fire to have a starting point.
For instance, I want to know how much difference there is between a floating and non floating firing pin design.
The measurement does not have to be extremely accurate, just consistent.
The holding jig must be designed to make it easy to change the bolts and put them back in the same position..
I have emailed Brownnells to see if they have any suitable gauges but have not received an answer.

#9 bruski

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Posted 06 January 2012 - 06:05 AM

Try pulling the bullets on several cartridges and dump the powder from them. Then mark each brass with a different color of marker or write on them the spring and pin shape. After snapping the pin on the brass measure the rim with a dial caliper for the thickness of the rim after firing it. Hopefully you should hear a small pop from the primers going off with each test.
bruski

#10 Steve McKuhen

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Posted 06 January 2012 - 04:30 PM

Brownnell just answered my email. They say they do not have any equipment and they also do not know of any other source that does.

#11 Sparky_NY

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Posted 07 January 2012 - 11:47 AM

Brownells has dummy rounds which are real ammo with no primer or powder and a tiny hole dead center in the base to show it as such. I bought a couple boxes for testing gun functionality.

How about a piece of scrap, drilled to hold a dummy or previously fired case in that bore stopped by the rim. Take a tenth dial indicator with a sharp tiny point and measure the depth of the firing pin hit in relation the the flat base. The harder the hit the deeper the dent. Alternately, homemade dummy rounds could be turned on the lathe from softer materials to increase the sensitivity of the method.

#12 shred

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Posted 08 January 2012 - 10:33 PM

Try pulling the bullets on several cartridges and dump the powder from them. Then mark each brass with a different color of marker or write on them the spring and pin shape. After snapping the pin on the brass measure the rim with a dial caliper for the thickness of the rim after firing it. Hopefully you should hear a small pop from the primers going off with each test.
bruski

It'll be somewhat loud. Ear protection may be advised. I did this while tuning my little 1919. Don't underestimate the power in a rimfire primer. You would need a pretty sharp caliper point as well.

From my experiences with the .22 1919, the keys to good ignition are firing pin tip shape (the wedge referred to before), the depth & location of the hit and how well seated the rim is against the chamber (often overlooked, but a big energy-stealer). I picked up a number of empties fired from commercial firearms at my local range and examined them under magnification and tried to duplicate the strike size, position (radially) and depth. If you're careful with your markings you can rechamber empty brass several times to get comparison hits. Under 10x magnification, it will be obvious which are adequate and which are not.

The Brownells dummies in the 50 round box are actual rounds that were never loaded with powder or primers, so after a few trips past the firing pin, they get kind of dinged up.

#13 Steve McKuhen

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Posted 08 February 2012 - 09:47 PM

I was able to find a used force gauge on ebay. It turned out to be damaged and missing parts. I was able to make parts. I did not know what the missing parts looked like but I got it to work.
I made a fixture to accept a shell with the lead removed. It will measure the force needed to fire the shell.
I have only tested several old bolts and only two spring sizes. The maximum on each is 20 lbs. and 18 lbs. This is a good test as you can feel what is going on. Two things I noticed so far is that the bolts drag a little and there is too much pressure on the firing pin ring as it rubs the groove in the cocking ring.
I need to make new test bolts and get more springs. Then I can start collecting test data.

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Shell with lead removed on end of force gauge.

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Firing pin cocked. An old cocking ring used as a trigger.



#14 Steve McKuhen

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Posted 24 February 2012 - 09:40 PM

As some of my experiments involve putting ball bearings on the end of the firing pins I added a torque gauge to the firing pin test stand. The gauge is attached to the cocking ring. By turning the torque gauge until the firing pin is let go the torque requried can be measured. This will let me know if my bearing ideas are valid.
These are old, used instruments. I do no know if they are accurate but they do give me an idea of which bolt configuration uses less force.
I have always thought that the firing pin dragging in the groove of the cocking ring adds to the overall pressure of the cocking handle. Now I have a consistent way to measure this pressure.
I have another torque gauge that I can add to the ggun test stand.

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This configuration measures 9 ounce inches of torque and 16 pounds of striking force. Roller says he calculates he fires at a little over 3 pounds. I have found that at 3 pounds the firing pin does not make a mark on the rim. The lowest pressure that fires a shell is about 8 pounds. I need to find a known weight to test the gauge. I had a 5 pound lead weight but I can not locate it.




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