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Double Rifles, Single Shots & Combinations >> Building Double Rifles & Gunsmithing
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doubleriflejack
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Reged: 11/11/07
Posts: 352
Loc: Oregon, U.S.A.
Bushing firing pin holes, vent holes necessary?
      #125013 - 24/01/09 10:30 AM

In using shotgun actions in making double rifle conversions, when bushing the firing pin holes, following Neidner/Mann safety firing pin gasproof and blowout proof process, is it necessary to drill small vent holes, one per bush, to allow excaping gas to follow path to side of action, or will gas escape to the side, without such holes? Ellis Brown, in his book, converting shotgun actions to double rifles, he goes into detail about such bushings, but makes no mention at all of using vent holes. I have seen old double rifles with such vent holes, but don't see them on more modern doubles---why? By the way, a very old law in Germany, requires German gunmakers to install firing pin bushings on all guns with rifled barrels. Look what happened to one of early rifles built by Ellis Brown, with pierced primers during proof, in his book, and you will be (should be) convinced of the wisdom of bushing firing pin holes properly. Not only can it destroy your stock, but it can also ruin your whole afternoon! If you think vent holes are necessary, what diameter would you think appropriate?

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MacNaughton360
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Reged: 10/12/07
Posts: 99
Loc: Indiana, USA
Re: Bushing firing pin holes, vent holes necessary? [Re: doubleriflejack]
      #125015 - 24/01/09 12:15 PM

I seem to recall seeing small grooves or channels in the breech face of some doubles extending from the centers of the firing pin holes at about 30 degrees above the horizontal, to the edges of the breech face. I believe one was an Ernst Steiglitz 9.3 X 72N.
I'm with you, there is a need for some gas relief, I will probably vent my double Francotte 16 if I convert it to a rifle. It needs striker bushings also.

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Marrakai
.416 member


Reged: 09/01/03
Posts: 3563
Loc: Darwin, Top End of Australia
Re: Bushing firing pin holes, vent holes necessary? [Re: MacNaughton360]
      #125040 - 25/01/09 01:34 AM

I think many people miss the point about bushing firing pins.

It is done to prevent gas escape from blown primers!

If a firing pin and associated hole in the breech-face are too large, the pressure from firing will push the firing-pin back and the primer will expand into the hole, either locking the gun closed, or in extreme cases rupturing and blowing gas into the action as per the Ellis Brown example. If the firing pins are correctly bushed, using modern reloading components, there will be no escaping gas to redirect!

The old Scott patents for gas-ports in the breech-face were 'invented' at a time of black powder, corrosive primers, weak metal alloys, and questionable reloading practices in the colonies. There is no need for them today, which is why no contemporary maker gives them a second thought.

--------------------
Marrakai
When the bull drops, the bullshit stops!
--------------------------------
www.marrakai-adventure.com.au

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André
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Reged: 28/06/04
Posts: 254
Loc: Brussels (Belgium)
Re: Bushing firing pin holes, vent holes necessary? [Re: Marrakai]
      #127843 - 23/02/09 09:37 PM

High quality modern day double rifles mostly have gas venting hollow screws. Generally they go unnoticed because they are covered up by engraving. As an example, here a pic of the action of my FN-Browning CCS25 in 9,3x74R showing the (engraved) gas screws :



Looking closely, you will pick up the slot and silhouette of one engraved screw in the scalop at upper chamber's mid-height. The lower bbl. screw sits in the middel of the action (engraved acorn), in line with the 1st.

--------------------
André
---------------------------------
3 shots do not make a group, they show a point of aim or impact.
5 shots are a group.

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DarylS
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Reged: 10/08/05
Posts: 26873
Loc: Beautiful British Columbia, Ca...
Re: Bushing firing pin holes, vent holes necessary? [Re: André]
      #127869 - 24/02/09 03:41 AM

Marrakai is spot-on.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

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