Also full length resizing gives the cartridge "wiggle room" for the bullet to be self aligning with the bore. And I belong to the Rat turd in the violin case club. :cool:
Below Kevin Thomas of Team Lapua USA and who also worked in the Sierra ballistic test lab.
https://i.imgur.com/Y3IiYL5.jpg
Below German Salazar from the "Rifleman's Journal is answering a question about "partial full length resizing". And he is explaining the benefits of full length resizing and how it helps minimize the effects of neck runout. Also the military considers .003 or less neck runout to be match grade ammunition.
Reloading: Partial Neck Sizing
by German A. Salazar
http://riflemansjournal.blogspot.com...ck-sizing.html
"Now the last scenario, a full-length sized case in which the neck is also fully sized. There is clearance at the neck and in the body of the case, the closest fit anywhere is the bullet in the throat. If the neck to bullet concentricity is good (although it needn't be perfect), then the bullet will find good alignment in the throat and the case body and neck will have minimal influence. Let's not forget that the base of the case is supported by the bolt face or the extractor to a certain degree as well; this is yet another influence on alignment. As you can see, there are several points from base to bullet that can have an effect. My procedure is to minimize the influence of those that I can control, namely the case body and neck, and let the alignment be dictated by the fit of the bullet in the throat and to some extent by the bolt's support of the base. Barring a seriously out of square case head, I don't think the bolt can have a negative effect on alignment, only a slightly positive effect from minimizing "case droop" in the chamber. Given that a resized case will usually have a maximum of 0.001" diametrical clearance at the web, this isn't much of a factor anyway."
My point being it doesn't do any good to neck size a case that warped and became banana shaped after firing. Full length resizing helps reduce the effects of a case with unequal case wall thicknesses meaning the average Remchester case. And a runout gauge can check for warped cases.
Its a shame but American quality control is governed by the company shareholders and a major reason why so many people buy Lapua brass.
NECO CONCENTRICITY, WALL THICKNESS AND RUNOUT GAUGE http://www.neconos.com/NEWDIAL2.JPG
Also referred to as "The Case Gauge," this item is designed to measure:
1) The curved "banana" shape of the cartridge case;
2) The relative wall thickness variation of a cartridge case;
3) The cartridge case head out-of-squareness;
4) Individual Bullets - out-of-round "egg shape" and/or
curved "banana" shape (excepting very small bullets);
5) The seated bullet and cartridge runout of loaded rounds. The accuracy of any firearm is determined -- and limited -- by the quality of the ammunition shot in it. The effect of imperfections in ammunition is cumulative; each flaw adds to the influence of all others. Precision shooters spend much time and effort "uniforming" cartridge cases, using advanced techniques to eliminate variation. Yet until recently, one of the most important of these variations has not been susceptible to detection by any device readily available to marksmen.
Normal manufacturing tolerances cause brass cartridge cases to vary in wall thickness around the circumference of their bodies. Under the stress of firing, a case with such variation stretches more readily along its thin side, transferring more pressure to the bolt face at that point and introducing an unbalanced force which contributes to bolt whip and vibration of the barreled action in its bedding. This whip and vibration varies from one shot to the next as cartridges are fired with their thin sides randomly oriented at different angles, causing reduced accuracy. The problem is made even worse if the brass is too hard or springy to completely fireform to the shape of the chamber, in which event the greater stretching of the case's thin side will cause it to develop a curve along the length of its body. These "banana" cases cannot hold a bullet aligned with and centered in the bore, undercutting the effectiveness of the handloader's careful case preparation.
Fortunately the accuracy problems caused by wall-thickness variation can be minimized, or perhaps eliminated, if all cases are "indexed" -- fired with their thin sides always oriented the same direction in the chamber. This causes bolt whip to be minimized and consistent, and, while bullets will still be misaligned, they will all be misaligned the same way, which often produces accuracy like that of perfectly aligned and concentric ammunition.