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Old December 24, 2012, 06:33 PM   #3
Join Date: March 4, 2005
Location: Ohio
Posts: 13,648
In general, if you have data for a bullet of similar construction (i.e., jacketed, cast, plated, solid copper) but of different shape, the loads will work if you can use the same seating depth and still have the round fit your magazines and feed properly.

Seating Depth = Nominal Case Length + Bullet Length - COL (Cartridge Overall Length)

Use that formula with the known load (you may have to call to find the bullet length if you don't know it; there is also a partial list, here) to learn its seating depth. Once you have that, then rearrange the above formula to find the COL you need with your different length bullet to get the same seating depth:

COL = Nominal Case Length + Bullet Length - Other Bullet's Seating Depth

If the other bullet, loaded to that new COL does not fit your magazine or feed, you are going to have to reduce the charge and seat a little deeper. Basically, you want to keep the percent of the empty space occupied by the powder underneath about the same for the new load. So if your deeper seating depth reduces that space by 10%, then you want to reduce the powder charge about 10%. This doesn't work perfectly, but it's a good approximation to start with.
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