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Double Rifles, Single Shots & Combinations >> Building Double Rifles & Gunsmithing

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.375 member

Reged: 20/04/11
Posts: 704
Loc: Hamilton, Montana
Question for Double smith's:
      #303163 - 21/07/17 01:10 PM

What in your opinion would be the minimum/maximum firing pin diameter to give reliable ignition, when the pin location is slightly off center of the primer?


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Reged: 29/12/14
Posts: 68
Loc: Lititz, PA United States
Re: Question for Double smith's: [Re: aromakr]
      #303433 - 30/07/17 03:28 AM

There is way too much information missing from the question to even guess at an answer.

There is far more to ignition reliability than firing pin diameter.

- radius of firing pin nose
- weight of firing pin
- length of firing pin (at both ends)
- firing pin travel distance
- hammer impulse (itself a function of mainspring stored potential energy, hammer weight, pivot location, travel distance - A.K.A. moment of inertia)
- headspace

The reality is that there is likely no answer to your question. Given all of the variables in construction just between primer brands, what works for one may not work for another.
Some of those variables are:

- primer cup hardness
- anvil design
- priming compound sensitivity

Has the rifle always suffered ignition reliability problems?
How far is "slightly off center"?

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Reged: 19/01/13
Posts: 82
Loc: South Carolina
Re: Question for Double smith's: [Re: DeweyVicknair]
      #303475 - 31/07/17 11:45 PM


"Slightly" off center of a large rifle primer is about .010" to my mind.

It is likely that millions of military rifles were built with "slightly" off center firing pins to the center of the rifle primer and further that these rifles functioned as designed and were within the design tolerance.

As such, if a rifle firing pin is "slightly" off center and the cartridge is not firing, then other issues are at fault.

It should be noted that double rifle's center point of firing pin to the cartridge primer center will change (move upward) the more the DR is used because the barrel flats get nearer the actions flats as the hinge pin and the forward lump hinge pin hole wear. However, these DR's continue to fire with this slightly off center change.

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