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November 23, 2011
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The idea of making a 40 Mag is not new. Before the 41 Mag came along there was the Herters 401 Power Mag.
The assumption: A 357 maximum cylinder can be bored out to accept 40 S&W, 10 mm and 40 Mag ammo.
Known Problems: Source of affordable brass. Answer 30-30 Win brass can be cut down and blown out (.003) to make 40 Mag ammo. Rim of 30-30 will need to be turned down by (.014).
All rounds will need moon clips due to thinness of 30-30 case head.
357 maximum extractor will need to be exchanged with 41 Mag extractor.
40 Mag ammo to have same AOL as 41 Mag
357 maximum cylinder will need to be shorten to reduce bullet jump before engaging rifling. This will require a longer 40 cal. barrel to fit existing shrouds.
Remaining known questions to be answered.
Finding pistolsmith to take on the project.
Does CZ have 357 maximum cylinder?
Finding the source for correct moon clips. Clips for the 40 Mag. will not work for the 40 S&W and 10 mm.
Finding source for custom barrel.
Question for the Forum Members. What have I overlooked? What do you think of the idea? If I pull the trigger on this project I will post an invitation for those that want this conversion.
R S
40 Mag Dan, How cool is that??
October 27, 2009
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I would do 10 mm magnum. Pretty much the same thing but brass is available. I had my s&w 610 converted to it. This would also be a waste in a stretch frame gun. Should just do 414
March 15, 2011
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Hello Rod:
I'd hold up on that "bullet jump" cylinder length reduction thing. I know my Ruger Redhawk 357 magnum revolver shoots extremely accurate with 38 WCs and the bullet jump is somewhat significant compared to the 357 magnum's leap to the forcing cone. I just looked at my 9mm project and the bullet nose is waaaay far back into the chamber on my 714. Let me report back on it accuracy before you decide to go there. DW41F.
November 23, 2011
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Thanks 41 mag. I have put the 40mag project on hold. Every thing was a go until I realized I would have to moon clip the 30-30 brass. I had settled on a Dan Wesson 360 cylinder bored out to 10mm. The machining of the rim would require me to get a metal lathe which drove the cost up to the point where I could have another Dan Wesson. Thanks for your feedback. R S
Remembering Col. Jeff Cooper
November 23, 2008
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Greetings
4 Years back I got a 414 SM cylinder from DW/CZ. Fitted that th o my 375 receiver. Numerous smith can take a .410 groove barrel blank, shape it and thread it. I used the sevices of John Taylor in Oregon. So for under $300 Istill have a 375 SM that will convert to 414 SM in about an hour.
I would go to 414 SM.. No hastles and a great caliber with 280 grain molds out there.
Have done the same with a 357 frame to 32/20.
Next I plan a 41 mag to 45 Colt.
Mike in Peru 
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