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Old May 8, 2013, 07:57 AM   #16
Senior Member
Join Date: October 18, 2006
Posts: 7,089 are going about this wrong.

Accuracy comes from the bullet leaving the muzzle at the same velocity, at the same position of muzzle whip, without being unduly disturbed by the following escaping gasses. That is it for what makes accurate ammo.

Now that you know what you are trying to achieve you have to think backwards on how to achieve it.

Pressure curve comes from two things, assuming brass and bullet seating is uniform, the powder and primer.

You get that by finding a powder charge range that provides consistent velocity with low SD. You don't need a chronograph to do this, you can use Dan Newberry's OCW method, a Ladder method, or even trial and error.

Since we don't have access to the equipment needed to measure primer strike to powder ignition times, finding the primer that works best for you can be a matter of trial and error. This is why hotter primers are recommended for hard to ignite powders even though hotter primers generally increase velocity SD due to initial pressure differences.

As far as uniforming flash holes, I don't bother. Once I get a load MOA or less I'm happy with it and I've never needed to uniform primer pockets or flash holes to get there. If you are shooting benchrest, then my loads are in no way competitive so flash hole uniforming is a really good idea.

Now, getting on to uniform brass and bullet seating.

Brass volume is a huge factor in determining pressure curves, the more consistent the volume the more uniform the pressure curves produced by your powder charges. I sort brass by brand, this is normally good enough for MOA or tighter ammo.

Bullet seating has already been explained, but you really do want that bullet to go into the bore true to the axis so that it doesn't get smooshed out of true.

Hope this helps,
Machine guns are awesome until you have to carry one.
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