Re: Neck tension-- how much ???
Good question, easy answer. Not simple to explain because it runs counter to what is commonly understood about bullet tension. I'll try.
Basically, Mikecr is absolutly correct, "best" "tension" is 1 to 1.5 thou. In fact, it isn't physically possible to even have more than about 1.5thou.
What most people call "tension" isn't. What they mean is how much smaller the neck ID is than the bullet, that's what machinests call an "interference fit", a jam-fit actually. Tension is NOT properly the amount of force needed to jam the bullet in, it's really the amount of pull required to take it back out.
Our cases have enough elasticity, or spring, in them to allow them to retain a springyness that holds the bullets in place. But, if it's stretched too far the elastic of limit of the brass is exceeded and it just permantly stretches/expands. (That's what happens when we fire the rounds, the neck is "permanently" stretched too large to hold another bullet until we "permanently" squeeze it back smaller.)
The elastic limit of common case neck brass is about 1 - 1.5 thou, rarely as much as 2 thou (it does vary a little by the physical size of the neck). If your .338 neck was sized and ball expanded to .330 your bullets will have to stretch it to .338 during seating. That much difference requires a noticible force to push them in and some feel that means it will hold the bullets tighter; it doesn't. You can prove that by seating, measuring the neck diameter, pulling the bullet and measureing it again; it will likely spring back only 1-2 thou from loaded diameter. Proving that no matter the neck diameter before seating, the permanent difference will only be 1 or 2 thousants (depending somewhat on how and where the measurements are taken and the original diameter of course). Thus, we can permanatly expand with an expander OR with a bullet but the end tension will be the same in either instance. There is no bullet tension value to expanding a neck to less than about 2 thou under bullet diameter.
One significant factor in having lower seating tension (in your case that would ideally mean an expander of .336"- .337") is that less force needed to push the bullets in so they will enter more easily and, from that, tend to go in straighter.
One rarely understood value of the Lee collet neck sizer die is it frequently achieves a proper REAL bullet tension fit.
Last edited by boomtube; 03-18-2010 at 03:52 PM.