04 April 2008
I'm going to assume you are referring to how much neck tension I use.
I use only as much neck tension as is necessary to push the bullet firmly up into the throat so that it is sealed before it is fired. I seat the bullet out far enough that it pushes back into the case neck around .020” when the bolt closes into battery. When it pushes back, you are then sure it got shoved up into the freebore so that the freebore of the throat can now guide the back end of the bullet as it moves out of the case.
I throat my guns so that only the gas check and a little more of the bullet is in the neck before I chamber it. The case is only used to introduce the bullet to the neck and not to guide it upon firing. That job is done by the throat which is solid and lined up with the bore better than the case.
If you get too much neck tension, your hand will get sore forcing the bolt closed and pushing the shell into the chamber. Also, it's hard on the locking lugs and they will soon gall if you force them to push the bullet in too hard. Additionally, if you use too much neck tension, soft and medium hard bullets can be sized undersize by the neck and you lose control of you bullet dia.
Some may want to size the bullet so that is slips into the throat more easily without so much force by the bolt. To check to see if you are getting a slight interference fit in the straight cylindrical part of the throat, simply pull a round back out and examine the first driving band on the bullet and you should see a witness mark there indicating that it did seal up and size down slightly when pushed up into the throat by the case. If you don't see anything start increasing sized dia. in .0001” increments till you see the witness mark.
When you achieve a fit like this, the bullet will obturate (not obdurate) right away and seal off gasses from escaping along side of it and damaging the bullet and stripping the lube from the bullet before it enters the bore.
I once set a gun up for a man who had a slight build and small hands. He had trouble forcing the bolt closed and got sore hands shooting a match. I have big strong hands and it was OK for me. Everybody's mileage varies.
This system takes advantage of the fact that the throat holds the bullet securely rather than to rely on the case neck to do it. Incidentally, I use tight neck chambers that require the case necks to be turned to .001” clearance in the neck of the chamber with a seated cast bullet. Since bullets are quite malleable, I've gotten away with zero neck clearance but I wouldn't recommend any else to try that.