Floating firing pin measurement
Posted 21 December 2011 - 02:11 PM
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.
Posted 21 December 2011 - 10:48 PM
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.
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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Posted 05 January 2012 - 02:31 PM
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....
Posted 05 January 2012 - 03:57 PM
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.
Posted 06 January 2012 - 06:05 AM
Posted 07 January 2012 - 11:47 AM
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.
Posted 08 January 2012 - 10:33 PM
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.
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.
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.
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.
Posted 24 February 2012 - 09:40 PM
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.
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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