Re: neck size or full length size?????
There's a popular belief that tight chamber necks are the best way to align the bullet with the bore. I don't believe that. Neither do others who use standard SAAMI chambers and properly full length size rimless bottleneck cases producing accuracy equalling and often exceeding what the "tight neck" folks get. Consider how a rimless bottleneck full length sized case with headspace 2/1000ths shorter than the chamber fits that chamber when the round's fired.
When the bolt's closed on the round and it has a plunger-style ejector pushing against the case head, that pushes the round as far forward in the chamber as possible. The round is now pressed into the chamber shoulder that has the same angle as the case shoulder. Which perfectly centers the round's front end in the chamber. Bolts with a Mauser style external ejector will close on the round and varying amounts of clearance between case head and bolt face as well as case and chamber shoulder will happen, but it doesn't matter. Meanwhile, at the back end of the case, the extractor's pushing the case sideways until it bears against the chamber wall. How far off center the case axis is from the chamber axis at the back end depends on the difference in diameters of the case and chamber, but it's only a couple thousandths regardless of how the fired case was resized.
Along comes the firing pin and strikes the primer. With all that force smacking the case, it's going to move foward hard against the chamber shoulder. As both case and shoulder angles are the same, the case shoulder will perfectly center itself at the front end of the chamber. It doesn't make any difference how much clearance there is between the case and chamber neck. If the case neck's off center to the case shoulder, it'll be off center when the round fires. And all that force from the firing pin also sets the case shoulder back a few thousandths; how much depends on the area of the shoulder and its angle as well as how smooth the two surfaces are. And the back end of the case may well move a bit sideways from that firing pin's impact, too.
Measure a primed case's headspace, chamber and pop that empty primed case, then measure its headspace to see how far the shoulder was set back. One can load several cartridges with each one a grain more less than max, the shoot them measuring fired case headspace after each shot. When the charge gets down to around 10% less than max, the cases will be shorter in headspace and their primers will protrude a bit indicating pressure wasn't high enough to stretch the case body back to where the head stops against the bolt face. Reducing the charge further results in the primer protruding even more. This usually proves to people that the case's front end gets centered in the chamber when it's fired and the case shoulder gets set back. But those cases may not have their shoulders moved forward far enough from full length sizing so they should be scrapped.
All of which means all rimless bottleneck cases end up a bit crooked in the chamber when the bolt's closed and the round's fired. Their back end's pressed sideways against the chamber wall but their front end's perfectly centered where it counts. Any difference in the angle between full length and neck only sized cases is insigificant. If one's ever measured the difference in bolt head positioning on a chambered round that's partially neck sized and the bolt binds a bit when closed, they might want to compare that to where the bolt head ends up on a chambered, full length sized case that has a couple thousandths headspace clearance. Especially if the bolt face hasn't been squared with the barrel thread axis. Bolt heads need to be at the same place for each shot for best accuracy.
Using gelded full length sizing dies (those without balls) to set a fired rimless bottleneck case shoulder back no more than 2/1000ths has been used to reload .308 Win. cases over 50 times; without annealing. Body diameters need be reduced only 2 to 3 thousandths. Accuracy has exceeded what benchrest records from neck sized cases are with this case so sized. Sierra Bullets' been using this process since the early 1950's for their rimless bottleneck cases used to test their bullets for accuracy. They don't weigh charges, either, just meter 'em direct into cases. Their best 30 caliber match bullets have shot into the ones (under 2/10ths MOA) from proper full length sized cases.
Regarding bullet seating, my full length sized bottleneck cases, both rimless and belted, full length sized with gelded dies end up with bullets seated with standard seating dies (such as the one that comes with a set of full length dies) just as straight as four different makes of competition dies. Bullets align themselves with case necks. If the neck axis ain't aligned with the body axis, no seater will put bullets straight in those cases.
Last edited by Bart B; 12-21-2009 at 07:59 AM..