Seating depth-precision delta


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Daniel1120
December 4, 2008, 09:33 PM
Got some 9mm 124 gr rn from them, but don't know what depth to seat them at, can't find anything on their site either. Any help?

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Chief-7700
December 4, 2008, 09:39 PM
What do your reloading books state for COL?
Chief

Daniel1120
December 4, 2008, 09:42 PM
Lee says 1.150, and speer says 1.135.
That is using the 125 gr jacketed from the lee book, it doesn't list unique with 124 grn.

rfwobbly
December 5, 2008, 12:14 AM
Daniel -
If you'll study the manuals closely you'll probably see that for the same type of powder, the cartridge with the shorter COL also calls for less powder.

For a given bullet, a shorter cartridge means the bullet is seated deeper in the case. The deeper the bullet is seated, the smaller the volume remaining inside the case. A smaller volume requires less powder to burn to achieve the same chamber pressure. Follow?

The volume inside a 9mm case is tiny as compared to something like a 38 Spl. So on a 9mm, small volume changes means big swings in chamber pressures.

Daniel1120
December 5, 2008, 11:37 AM
You are exactly right. I was wondering why lee's min and max charge was a well below speers. Makes perfect sense now.

Now should I seat the bullet to lee's depth or speers? If im using the same components everytime I would rather not have two seating depths.

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