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Gosh

I was just posting some pictures.

The action is a Zabala Magnum 12 guage. Sold in some countries ( not this one) as the model 213 I believe.

The reason that I chose that action is that it is proofed to 1370 bar for 3 1/2 inch 1 5/8 oz 12 guage shotshells and by design it was intended to discharge both barrels simultaniously.
If one looks at it in kenetic energy terms. There is an equal and opposit reaction to the discharge of a projectile. So 1421 grains of shot at 1400 fps is 6158 ftlbs to be dissapated throughout the action. As opposed to about 4800ftlbs for the 450 No.2.

Now I cannot find my calcs tonight, but the breech thurst is also far greater than the 450 No.2 from all the figures that I have been able to glean.
This is also why I have not been too concerned with a third fastner in this action. Biakial are building some doubles in 30-06 I believe without the third fastner and to put it politly without a great deal of quality control. I believe that the breech thrust is greater than 450 No.2 These are being imported to the states and in that litigious society I would expect that somebody tried very hard to blow one up before that decision was taken.
In terms of hoop pressure resistence modern steels as so much stronger than the turn of the century ones that this gives me little cause for concern.

IMHO it is also not enough simply to look at the cahmber pressures of two or more cartridges. One must also look at the surface area accross which that pressure is conducted to determine the breech thrust. Given that the barrel has sufficient hoop resistence/strength then this is the critical factor. This is the principles applied in hydrolics with differing size cylinders ect and many others.
If you think of a real world analagy you can stop the flow of a 1/2" garden hose connected to the main water by putting your finger over it. Try that with a 4" main at the same pressure.
Knowing the force is not enough, one must relate that to the area accross which it opperates.

The bottom line however is that provisional proof will tell the tale. I am lucky that the London proof house is only 4 miles down the road. I wonder if they charge extra if they have to pick bits of 4140 out of their ceiling??

As to the economics, I could, if I wanted go to the safe and buy a cheep double tomorrow ( not an English one unfortunatly

) For me personally it is not just about saving money, it is also because I enjoy doing it and there is a satisfaction to shooting something that you built.
What I build will never compete with H+H or Purdy, nor is it intended to but it will be a part of me in a way that even those masterpieces never can.

Anyway if my wife is reading this over my shoulder that is my excuse for all those after work hours spent in the workshop

PS Shall I continue to post pics as this progresses??

Regards

Edited by Bramble (08/10/06 11:35 AM)

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