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Old January 10, 2013, 01:34 PM   #4
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 4,809
Unclenick, your info's good. Thanks for posting it. Salazar's article is one I'm familiar with. Most interesting to me is his cartridge spinner. It gauges bullet runout relative to the case body angle as it rests on the gauging rods. As virtually all cases are a bit out of round, that'll show up in his bullet runout numbers. And a rimless bottleneck case body's not what centers the case in the chamber up front where the bullet is. A .30-06 case shoulder is what centers the front of the case in the chamber when the round's fired; exactly like a NO-GO headspace gauge does in a GO chamber when the bolt closes. The body only touches the chamber at its back end where it could be anyplace but typically is somewhere against the chamber wall being pressed there by the extractor force. I think it's better if the front of the case is held by a round hole in something (I've used nylon washers) that represents the chamber shoulder and it's about mid point on the case shoulder. The back end of the case body at the pressure ring could rest between two points such as rollers or a V block.

'Twas either the US Army or Marine Corps Rifle Teams that tested M118 ammo in M14NM's machine rested at 600 yards some years ago. Ammo with more than .003" runout opened up their many-shot test goups. Less than that, there was nothing significant in accuracy. I've not seen any accuracy degradation in my .308's and 30 caliber magnums with runout max at .003". That has about the same bullet angle as .002" runout for 24 caliber bullets.

One thing I've noticed is crooked bullets seem to have less accuracy when seated so they're not into the lands when chambered. When bullets seat into the lands when chambered, that tends to improve accuracy over jumping into them.
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Last edited by Bart B.; January 10, 2013 at 05:41 PM.
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