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Old December 26, 2012, 08:58 PM   #6
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Join Date: November 8, 2007
Posts: 2,001
but what about the length. The 9mm case is so short. Will pressing the longer bullet into it, increase the pressure outside of the normal?
YES it will.

For two reasons:

1. If the bullet is "longer" then it is probably also heavier, which will definitely increase pressure.

2. If the bullet is longer, it will still need to be seated to nearly the same overall cartridge length in order to feed it from the magazine. That will leave less space for the powder and can raise pressures catastrophically in such a small case.

There is also a third reason that is not quite as significant as the two above: the larger diameter bullet is harder to swaged down into the bore and rifling, which also raises pressure. It might also be large enough to make it hard for the case to release the bullet in a gun with a tight chamber.

So, without a lot more study on your part, DON'T DO IT.

Once you area able to determine the amount of powder space in a case with a bullet loaded, the groove diameter of a barrel, and the clearance between the case and the chamber wall where the bullet is inside your case, THEN you can start thinking about whether you want to use a particular .357" diameter bullet in a 9mm chamber. But, you will certainly want to start from pressure tested data for the same bullet weight.

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