Thread: OAL or Ogive
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Old April 30, 2006, 04:01 PM   #7
Join Date: March 4, 2005
Location: Ohio
Posts: 13,727

Ahh, now you've opened a can of worms. Check Dan Newberry's Optimal Charge Weight theory out. Also look at his instructions for firing 3-shot round robins instead of Audette ladders. Interesting stuff.

Freebore has no reason to affect accuracy if it isn't loose. If it is loose enough to allow a bullet to cant, it will cause trouble, or if your bullet's side bearing surfaces aren't a true cylinder, it will allow canting. Touching the lands is just a way of using the taper and hole centering principle to be certain there is no cant. The conflict is the deeper seating tends to improve start pressure consistency, and improves accuracy for that reason. Seating a little off the lands lets the start pressure improve but also lets the bullet hit the lands at a low enough velocity that it still centers rather than ploughing onto the lead so fast it remains canted. The exact best point of compromise varies with powder burning characteristics.

Harold Vaughn reported that sizing Noslers down half a thousandth improved 300 yard groups from 3.5" to 2.5" in a .270 just by forcing the sides parallel.

In addition, if you have fixed your powder charge, seating depth affects accuracy by changing barrel time. Newberry blames the whole effect on this, but I don't agree. There are cases of the optimum seating depth being found first, then the powder charge afterward. So it is a mix of things. Newberry's ideas are here and fit will with Chris Long's optimum barrel time theory.

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