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Bart B. · August 12, 2012, 09:28 AM

mehavey, thanks for the screen shot of Quickload's bore/groove area input. That certainly effects pressure slope and peak numbers. But so does bullet jacket hardness as well as the chamber's leade angle; they're not all that easy for consumers to determine and that may be why these two pressure-changing elements ain't part of Quickload. But Quickload's probably the best thing out there to get a reasonably accurate answer. Too bad Oehler quit selling their pressure measuring systems; at least I think they did.

Regarding rimless bottleneck case fit in chambers after the bolt closed on them. They all rest on the chamber bottom (gravity?) when pushed into the chamber and the bolt's still open as there's no external force changing that. All of 'em (new, fired, or resized any way), after the bolt's closed have their back ends pressed against the chamber wall (typically at the pressure ring) by the extractor. If it's a sliding one in front of a locking lug as in a push-feed Model 70, it pushes the case up stopping against the top of the chamber (there's space between the bottom of the case body and chamber wall). Mauser style external extractors push the case head to the opposite side; left on a Win. 70 classic controlled feed right hand bolt. Up front at the shoulder, in-line ejectors in the bolt face push the round forward until its shoulder centers in the chamber shoulder centering it very well. And that well centers the case neck in the chamber neck. Even a .243 Win. round's neck is perfectly centered in .308 Win. chamber this way. With bolts having external ejectors, the back end of the case may be anywhere depending on several things. In either instance, when the firing pin smacks the primer, that drives the case forward hard into the chamber shoulder centering the round very well in the chamber up front. There's no "rattle space with either one; both are held very repeatable in centering up front. Neck only sized cases whose body diameters have grown where they interfere with the chamber walls can force the case neck off center in the chamber neck; 'tain't no such thing as perfectly round cases and chambers; cases are the worst of them.

In my measurements of case neck centering on case shoulders after sizing, I tried Neil Jones' neck/shoulder bushings set to size neck almost to the shoulder as well as bumping the shoulder back a thousandths. And also full length sizing them (in dies with necks lapped out a couple thousandths smaller than a loaded round's neck diameter) setting the shoulder back a thousandth or two. In all instances, full length sizing .308 Win. and 30 caliber magnum cases, necks were better centered on case shoulders when full length sized. I attribute that to a full length die holding the fired case body repeatably as the shoulder's set back while sizing the neck down.

August 12, 2012, 09:28 AM	#22
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	mehavey, thanks for the screen shot of Quickload's bore/groove area input. That certainly effects pressure slope and peak numbers. But so does bullet jacket hardness as well as the chamber's leade angle; they're not all that easy for consumers to determine and that may be why these two pressure-changing elements ain't part of Quickload. But Quickload's probably the best thing out there to get a reasonably accurate answer. Too bad Oehler quit selling their pressure measuring systems; at least I think they did. Regarding rimless bottleneck case fit in chambers after the bolt closed on them. They all rest on the chamber bottom (gravity?) when pushed into the chamber and the bolt's still open as there's no external force changing that. All of 'em (new, fired, or resized any way), after the bolt's closed have their back ends pressed against the chamber wall (typically at the pressure ring) by the extractor. If it's a sliding one in front of a locking lug as in a push-feed Model 70, it pushes the case up stopping against the top of the chamber (there's space between the bottom of the case body and chamber wall). Mauser style external extractors push the case head to the opposite side; left on a Win. 70 classic controlled feed right hand bolt. Up front at the shoulder, in-line ejectors in the bolt face push the round forward until its shoulder centers in the chamber shoulder centering it very well. And that well centers the case neck in the chamber neck. Even a .243 Win. round's neck is perfectly centered in .308 Win. chamber this way. With bolts having external ejectors, the back end of the case may be anywhere depending on several things. In either instance, when the firing pin smacks the primer, that drives the case forward hard into the chamber shoulder centering the round very well in the chamber up front. There's no "rattle space with either one; both are held very repeatable in centering up front. Neck only sized cases whose body diameters have grown where they interfere with the chamber walls can force the case neck off center in the chamber neck; 'tain't no such thing as perfectly round cases and chambers; cases are the worst of them. In my measurements of case neck centering on case shoulders after sizing, I tried Neil Jones' neck/shoulder bushings set to size neck almost to the shoulder as well as bumping the shoulder back a thousandths. And also full length sizing them (in dies with necks lapped out a couple thousandths smaller than a loaded round's neck diameter) setting the shoulder back a thousandth or two. In all instances, full length sizing .308 Win. and 30 caliber magnum cases, necks were better centered on case shoulders when full length sized. I attribute that to a full length die holding the fired case body repeatably as the shoulder's set back while sizing the neck down. Last edited by Bart B.; August 12, 2012 at 10:27 AM.