View Single Post
Old November 10, 2012, 02:54 PM   #27
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 4,707
Ah-ha. . . . the full-length versus neck-only fired case sizing issue raises its heads again......

And that animal (issue?) will continue to raise its head forever. If neck-only is the answer preferred, it is usually selected by folks who:

* Base a reload’s accuracy by the smallest few-shot test group shot claim the components, tools and techniques used to do that are what should be used and done. Doesn’t matter what the size of the largest group was ‘cause they’re believers that tiniest means most accurate as far as groups are concerned.

* Think the best alignment of a chambered round’s bullet to the bore can only happen when there’s minimal clearance between the case body and neck to the chamber body and neck. And therefore, the least a fired case is sized, the better, more perfect, best bullet alignment to the bore can only happen with fired cases so sized.

* Are convinced best accuracy has always been with benchrest rifles using neck only sized cases. And no other type of rifle could possibly shoot as accurate as the ones used in benchrest matches.

Those believers of such might want to consider the following facts:

* Sierra Bullets did what’s probably the most intensive and proper tests of all sorts of fired case sizing techniques with all sorts of tools back in the 1950's. Their ballistic technician wanted to use the tools and techniques that produced the most accurate ammunition in all sorts of barrels and chambers. They’ve been full length sizing all their cases used to test their product for accuracy since then. That’s for both super-accurate rail guns testing bullets for quality control as well as sporting rifles for load development in their reloading guide.

* Bottleneck ammunition cases center perfectly up front in the chamber when they’re fired. Most of them do so when they’re chambered before they’re fired. This happens because of the case and chamber shape and the external forces pushing on the loaded round before the primer fires. They do not rest at the bottom of the chamber; a claim often stated as what happens. Note that virtually every cartridge chambered has its back end pushed off center in the chamber until it stops against the chamber by the extractor; they're rarely perfectly centered at their back end.

* Full length sized bottleneck cases without expander balls but with neck diameters a couple thousandths smaller than a loaded round’s neck diameter end up with their neck better centered on the case shoulder than neck only sizing produces. Expander balls are not used.

* High power match rifles (normally shoulder fired) when tested for accuracy in machine rests with full length sized cases have produced many-shot test groups smaller than current benchrest records. Full length sized fired cases used in them’s been the match-winning and record-setting standard for decades.

* Benchresters have been moving to proper full length sizing for best accuracy; especially with maximum, hot loads.

* Best tests for ammo accuracy need to have at least 20 shots per test group. Then use the mean radius of all shot holes from group center for the measurement. Extreme spread is also good (if at least 30 or more shots pre group is used) as it represents the area all fired shots will probably go inside of.

Last edited by Bart B.; November 10, 2012 at 02:59 PM.
Bart B. is offline  
 
Page generated in 0.05842 seconds with 7 queries