Neck tension

[Awf Hand]

I've got a rifle with a .308" bore (I will slug it at my first convenience) and I'll be shooting GC bullets that can be sized anywhere from .308 to .311.  The .311 bullets are darned close to as-cast with only a slight smear when going through the sizing die.  Alloy is 92-6-2 and I'm using Hornady GC's.

I've also got a couple of diesets with a couple different sizes of expander balls to resize the neck of the brass.  Additionally, I bought one of the Lee Collet die sets and have a lathe available to make my own diameter collets.

While I realize that annealing and number of firings can influence the neck tension, what's a good place to start for:

Bullet to bore fit?

Brass to bullet fit?

I've done some shooting -with pleasing results, but still feel like I'm doing a guess-and-calc on a quadratic equation.  If I could get closer to the sweet spot without burning up all my primers, that'd be helpful.

Thanks in advance!!

[stimpylu32]

Awf Hand

My rule of thumb is to size the ID of the neck to .001 less than the bullet dia. and so far it has been working .

stimpy

[Nobade]

If the unsized bullets will chamber without resistance, they'll probably shoot fine. Then you can try sizing them down .001" at a time and see which shoot better. My rule of thumb is to size to no more than .001" under throat diameter. Don't care about groove diameter. If the bullet gets gas cut in the throat it's not gonna shoot no matter what.

[Larry Gibson]

Nobade is correct; size to the throat.  In most .308 rifles a .310/.311 sized bullet works best with most regular type cast bullets.  I've done enough testing of numerous .308 calibers that I now just use .311 as a rule of thumb id the bullet drops at least that size.  Yours does so I would recommend starting at .311 sizing.

Both Awf hand and Nobade are also correct about neck tension.  Let the feeding and chambering of cartridges dictate the amount of neck tension required with .001 being about the minimum.  Enough neck tension is needed so the bullet is not pushed back into the case during the feed/chambering cycle.  I multiple rounds are in a magizing (box or tube) then the bullets not moving under recoil is also a consideration.  Also a GC bullet will withstand more neck tension without damage to the bullet than a softer cast PB'd bullet.  Softer PB bullets can be sized down by the case if there is too much neck tension. Lastly you want as little as possible distortion to the bullet nose when seating it into the case. 

I've been using a Lyman .30 Mdie with .308/.309 cast bullets and a Lyman .31 M die with .310 - .312 cast bullets with excellent success for years.  This gives .002 - .003" of neck tension.  I also have a couple Lee collet dies (they work well) and several Redding Bushing dies.  With these I can custom taylor the neck tension for a given size bullet.

You will also want to clair the case mouth for cast bullets.

Larry Gibson