And to add to the above: neck sizing is only done on bolt action rifles. Any semi auto needs to be full length sized unless you like dealing with lots of feeding issues and malfunction drills. Some ar's with extra tight chambers even benefit from a small base sizing die. Mine do not, but there's plenty out there that do as seen on various gun boards. Either that, or them folks don't know how to set up a die which is entirely possible. Jamming the lands (loading long) IMO shouldn't be done by inexperienced loaders. It's very possible to increase pressure in the cartridge. Combine that with a max load, crimping, or an overcharge, and things can get messy quick. We are playing with 60,000psi a mere couple of inches from your face.
I know one thing after shuffling through and looking at some of the surplus ammo I've got boy do those rounds look terrible compared to stuff I've made. Weird lengths, deformed necks etc.
Yes I do agree with you on that bocefus78 I should've clarified the neck sizing is for bolt actions. And you are correct about the small base sizer die. I also found that anyone with a Savage model 99 always seems to have to use small base sizer dies as well, especially if chambered in a 300. Savage. And as far as neck sizing and loading long for competition yes leave it to the experienced loaders. As a gerneral rule of thumb for loading J. Dirt follow the book! If you have a load that is close but you want to tweak it to see if you can make it more accurate you can experiment with seating depths. This is where you would need a chamber gauge. You usually start with the ogive of the bullet 5,000 thousands off of the lands because that distance acts as a pressure relief valve. bocefus78 is right if the bullet is forced into the lands this can greatly increase the pressure! For instance all factory Weatherby chambers have a lot of free bore. This is how they obtain the increase of velocity. If you get a custom chsmbered say 300 Weatherby barrel you need to back you loads off because the custom barrels do not have the free bore that the factory ones do!
It's always a good idea if you buy new unprimed brass is to full length size it before you load it! You'd be surprised at how many actually resize.
You can neck size for autoloaders, not through a mag though. Most of the time the rounds made for match or accuracy aren't mag length anyway. Long bullets with full case volumes collet sized shoot great.
