CowboyT wrote:Depends. If you're firing the rounds out of a bolt-action or a single-shot, then neck-sizing can be quite beneficial. However, if we're talking about a semi-auto (some would argue a levergun, too), then full-length sizing is best. This is due to the strong camming that the bolt-action provides. Semi-auto actions might not have quite enough "oomph" to shove something a little oversized (like a fired case) all the way into the chamber. This can mean you don't go fully into battery, but maybe juuust close enough for the firing pin to hit the primer, and as some M1 Garand situations have shown us, that can be destructive to the firearm and possibly the shooter as well. That's one reason I'd feel much better full-length sizing for a semi-auto.
Basic rule is if you are going to shoot in the same rifle (and it isn't an auto-loader), you can just do next sizing. You are basically fire-forming the brass to fit that particular rifle's chamber. While all of the chambers for a cartridge have same basic dimensions, there are machining tolerances inherent in all manufacturing, and your individual chamber is just somewhere inside those tolerances, and onced fired the brass now matches those tolerances.
BUT - if you load for multiple rifles (or auto-loaders), then you should do full length, as all chambers vary a bit, and you want to get back to basic specs. If your two chambers vary in opposite directions, and you fire form in one and then shoot in the other, you can get at best some bad accuracy, and at worst, dangerous conditions.