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Old February 21, 2012, 09:14 PM   #2
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Join Date: December 24, 2008
Location: Loveland, CO
Posts: 1,475
What determines pressure is the bullet seating depth. So to get the same pressure as the load in the manual, use the same bullet and set it to the same depth. But life isn't ever that easy.

Since you aren't using the same pistol as the load was developed in, I always check a couple of things first. Will your loaded round chamber without the bullet hitting the rifling? I make up a dummy round and check before loading.

If the round will chamber at that OAL, calculate if the seating depth for your dummy round is the same as the load in the manual. You need to know exactly what bullet they used (not just weight and bullet type). I find lots of good data here. You also need to check to see if they will fit in your magazine.

If you need to seat deeper (shorter OAL, greater seating depth) then you will want to back off the powder loading. If you seat longer, you may need to increase powder loading. One of the reasons I like the Lyman manual is they list the actual bullet used. Of course the Nosler, Sierra, Hornady, etc. manuals only use their own bullets. This is why having several manuals is a great idea.

But knowing that changing the seating depth changes the pressure is a good starting point.
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