Comments on: TECH TIP–Neck Tension vs. Time

By: mac

mac — Sun, 06 Dec 2009 21:11:42 +0000

I have two set of RCBS 308 dies. One standard, and a competition die set. What will be the difference in the neck sizing?

What determines neck tension, and how is it controlled?

By: Keith

Keith — Tue, 26 Aug 2008 04:19:08 +0000

Forget to say that normal bushing I use is 2 thou bigger than the bushing I used this time. Have a .273″ nk which use fired yesterday, normally use .268″ bushing, used .270″ for this test and normal loaded round is .269″. This way the loaded round measures .271″ and the bullets seat easier, hope they still shoot Ha!

By: Keith

Keith — Tue, 26 Aug 2008 01:24:29 +0000

I concur — load and seat the bullet as soon as you can after sizing it.

Try this one you button loading guys. Size a case with your button die set so you are no where near the shoulder. Set it aside for 3 hours. Size another case, then size that same case again. You will feel the brass going into the bushing on the 2nd sizing. Now take the case that sat for 3 hours and size it again. I will bet you will not even fell it touching… zipo, nota. You would swear it was sized with a smaller bushing!

Size it, and reload it right away for a more consistent “feel” while seating the bullets.

By: Mark

Mark — Mon, 25 Aug 2008 17:12:14 +0000

The real question to me is the difference between older loaded ammo and immediately sized and loaded ammo’s grip on the bullet and how chamber preasure dynamics are effected. What is the required bullet lanch preasure and how does this dynamicly effect your load formula? Can the guage shown measure a bullet pull preasure? Maybe this will be a whole new area of loading anxiety? (ha ha)

By: Editor

Editor — Sun, 24 Aug 2008 23:44:35 +0000

Jim, what you wonder might happen is exactly what Jason Baney has observed, empirically, in loads made up for 1000-yard matches. He found it threw off the tune of his load if he loaded a long time before the match. Whether this is because of changed metallurgy, or some other mystery factor, we can’t really say. But the difference showed up on the chronograph (higher ES) and on the target (larger vertical spread).

Re the numbers (20 vs. 60) — keep in mind that the K&M simply has a dial caliper activated by a Bellville washer stack with a link rod. This isn’t an ultra-precise measure of force. But you CAN feel the difference between a 20 dial position and a 60. If you use the K&M you’d see what I mean–the needle tends to swing back and forth as the bullet is seating. I think what is going on is the resistance to seating goes up as the brass becomes less elastic over time.

By: Josh Benin

Josh Benin — Sun, 24 Aug 2008 23:14:20 +0000

Mr. McElwayne makes a fine point. It’s an assumption to leap from an increase in seating force to changes in brass, at least without additional data, or control for friction. It is difficult to accept the Editor’s comments on brass behavior without hearing from a metallurgist – these comments aren’t in line with typical behavior of metals.

By: Jim Berry

Jim Berry — Tue, 10 Jul 2007 00:36:56 +0000

Just a thought: If necks as sized are taking a set, what, if any, effect does ammo loaded more than a week before a match have, compared to those loaded only only, say, two days before or after arriving at the range? Will those loaded week(s) prior to shooting have greater neck tension? I’m a newbee, so please excuse me if this is off the wall.

By: Tom McElwayne

Tom McElwayne — Mon, 09 Jul 2007 16:43:41 +0000

Possibly the lubrication used to size the necks from two weeks past had dried. A delta of 20’s verses 60’s in substantial considering the same sizing button and operation. Regarding the ‘spring back’ effect verses time; seating force would tend to lessen not increase, otherwise the case mouth rebounds to the larger fire-formed diameter- right?

Quite an interesting observation at the very least. As for myself, I think more imperical research is required before drawing hard conculsions here.

Editor: Tom–you made a good point about the term “spring-back” because that is ambiguous. I’ve changed that. Basically what is happening, over time, is that the necks (as sized) are taking a “set” and seem to lose elasticity or the ability to stretch. When they are freshly sized, the neck material is more ductile and expands more readily as the bullet is seated.