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Firing Pin Diameter (Read 573 times)
Chuckster
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Colorado, Colorado, USA
Firing Pin Diameter
Aug 29th, 2012 at 9:46am
 
Follow up on the Axtell post. What is the correct firing pin diameter for the low pressure single shots we use? Have one about 0.075" dia. like high powers and tends to be sticky. Trapdoor is over 0.100", works but seems large. Has someone found a happy medium?
Chuck
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BP
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Westside, Washington, USA
Re: Firing Pin Diameter
Reply #1 - Aug 29th, 2012 at 3:56pm
 
Chuck,

You've asked a question that can get a bunch of different responses depending on...

It's interesting to examine the changes to the firing pins that WRA tried out in all their different rifle models just for the 22 RF to achieve what they thought would work best at the particulat time they made the change.

A lot of factors to consider - force imparted by the mainspring transfered through the hammer, angle of the pin in the block, along with possible diameters and nose shapes, hardness of the primer cup material (which varies somewhat amongst manufacturers and is always subject to change), and the primer type - pistol or rifle, and maybe even battery cup if someone has altered Berdan primed cases to reload.

Pretty hard to cover all the possible variables, and there are always trade-offs, so an "ideal" diameter can be tough to come up with.

I don't think WRA ever really found their "ideal" shape or "correct" diameter, so I wouldn't expect there to be an easy answer for us either, pretty much leaving us with... Whatever Works.

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frnkeore
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Re: Firing Pin Diameter
Reply #2 - Aug 29th, 2012 at 5:07pm
 
Chuck,
firing pins shouldn't be sticky no matter what their diameter if the fit is right and they are not bent. Your .075 pin should be good for at least 45k cpu. The higher pressure pins are about .062.

I like to make mine with .002 to no more than .005 clearance for both the body and pin itself(everything must be concentric).

If you have a rebounding hammer the pin needs to smaller than a non rebounding to keep the primer from flowing back into the hole.

Frank
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Chuckster
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Colorado, Colorado, USA
Re: Firing Pin Diameter
Reply #3 - Aug 31st, 2012 at 9:57am
 
Appreciate the replies. Was thinking a larger firing pin diameter might be better on actions without positive firing pin retraction, such as the Stevens 44 , Ballard, Sharps 1874, etc. Firing pin protrusion is somewhere in the 0.050-0.060 range, more than the radius of the pin nose. With a small diameter pin the cylindrical section of the pin is inside the primer and nothing to retract it.
Chuck
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