Before someone gets the wrong idea, I no longer load for the 300WM. I do still have a pile of brass with an untold number of firings on them. My disdain for neck sizing is not limited to a belted magnum. I have tried neck sizing with several including 6TCU and 7TCU with often dismal results. The 7TCU should be the greatest beneficiary of neck sizing, due to its rather sleight shoulder. Very easy to crush a 7TCU shoulder, when you do you will not know about it till you try to fire. This cartridge is very sensitive to headspace problems caused by improper FL die setup. Most guns chambered for this round had no camming action to crush the case into the chamber(break actions and falling blocks). If the case wasn't sized just right it may not chamber(easy to check and usually caused by neck sizing), or have excess headspace due to a crushed shoulder(won't fire, unless perhaps you have jammed the lands with bullet). I never had a problem with this tempermental wildcat, using the setup method I have described for you.
It appears Culpeper and I agree on this issue more than I thought. You can also have a situation where the FL die is actually unable to bump the shoulder enough with full cam over of the ram. This I why you hear tell of guys either surface grinding a shellholder, or buying the Redding BR set of shellholders. Luckily I have never needed either and I own some extremely tight chambers. If you have a factory chamber you are likely to have vast amounts of adjustment to get the proper shoulder bump. As has been said I think, chances are very good if you set up a FL die with heavy cam over,_just like many die instructions tell you to do, you will be grossly oversizing your brass. If you are loading for an auto you will need a bit more shoulder setback, as your primary goal should be function first.
Neck sizing is not new, nor cutting edge, it is in fact very old.
I don't hate gadgets and gizmos, I have owned many over the years fro reloading. I have sold most of them as I never found them to improve my efficiency or final results. I no longer own a tool to figure distance to the lands. You might be surprised how many 1000yd BR shooters don't own one, or no longer use one either. One tool I do own that is indispensable is my hex Sinclair bullet comparator, $20 well spent. And if you want to know your length to the lands in an actual measurement, you will need one. I make my own length to lands tools from once fired resized cases with a split neck, simple, and less than a dollar in most instances.
I need to start a sticky and label it,"Tips from the Old Curmudgeon on making world class ammo with home made tools and tricks."
PS:Expander plugs probably do cause severe runnout. It is a real bitch getting one centered in the die, so it would almost have to cause runnout. I will tell you another trick that will eliminate most if not all expander plug run out. I rig mine to float, and I have found it does make a difference. It works with most but not all dies. If your expander stem has a lock nut leave it loose. You should be able to wiggle the stem, this will cause it to self center as the case is pulled out of the die. You do need to be careful when you run the case in the die to let it find the flash hole. Another option is to deprime with universal die and use the poor mans floating expander with decapping pin removed. It works, I have done this for several years and my ammo has improved greatly. Yes my NECO concentricity gauge was sold years ago
