Neck tension on standard FL dies?

[SDHNTR]

Say you’re using a standard FL bushing-less die from any of the big names, Redding, RCBS, Hornady, Forster etc... is there a standard neck tension that is utilized across brands? Or is it all over the place?

 

[fightthenoise]

They typically size the necks down quite a bit, more than necessary, and then set final tension with the expander ball on the way out.

The proper way to use the dies you’re talking about is to remove said expander ball and run an expander mandrel through the neck in a separate step. That expander ball dragging through the neck on the way out can pull the necks and stretch the brass.

 

[ericwh]

My RCBS die, using the expander ball, was giving ~.003" neck tension.
My Forster die, using the expander ball, is giving ~.002" neck tension.

 

[SDHNTR]

My RCBS die, using the expander ball, was giving ~.003" neck tension.
My Forster die, using the expander ball, is giving ~.002" neck tension.

That's helpful. So I guess there is no standard.

 

[wapitibob]

I'm getting about .002 but the real problem with my full length sizer and expander ball is the sizer compresses my neck down .015 then expands it out. That's working the beejeezus out of the neck and why I anneal every firing and am going to a bushing die.

 

[Trippy]

My 7mm RM RCBS die provided .005" neck tension if that helps show the inconsistencies better/more. Collects dust now.

 

[SamsonMan22]

My RCBS 308 die ran .004” my Forster .308 is .002”. The RCBS small base die I use in my wife’s .308 is .002”. They all seem to vary between .002-.004” with all of the dies I have using the expander.

 

[N2TRKYS]

Wouldn’t the consistency between loadings(repeatability of neck tension) be more important than the consistency between different dies?

 

[fightthenoise]

In the context of this thread, the variable most affecting accuracy is runout induced by the expander ball. The neck expands and releases the bullet on ignition before the bullet ever begins to move.

Another aspect to consider is that you are only ever going to get about a spring back’s worth of squeeze on the bullet, which is about half to a thou worth. Sizing your necks down tighter (2, 3, 5 thou, whatever) doesn’t give you more grip. Your bullet just becomes a (crappy) expander mandrel, expanding the brass to cal diameter, and it’s still being held in by the spring back on the brass and the friction between the bearing surface and the sized portion of your neck. Think about what happens when your expander ball sizes the neck back out after sizing. The neck gets a little bigger, and bounces back about a thou. Same thing when you seat a bullet. The neck expands to cal diameter and bounces back about a thou. Anything more is just over working the necks and creating unnecessarily high seating pressures forcing your bullets to expand your necks.

 

[SDHNTR]

Wouldn’t the consistency between loadings(repeatability of neck tension) be more important than the consistency between different dies?

Yes, of course, I was really just curious.

 

[SDHNTR]

In the context of this thread, the variable most affecting accuracy is runout induced by the expander ball. The neck expands and releases the bullet on ignition before the bullet ever begins to move.

Another aspect to consider is that you are only ever going to get about a spring back’s worth of squeeze on the bullet, which is about half to a thou worth. Sizing your necks down tighter (2, 3, 5 thou, whatever) doesn’t give you more grip. Your bullet just becomes a (crappy) expander mandrel, expanding the brass to cal diameter, and it’s still being held in by the spring back on the brass and the friction between the bearing surface and the sized portion of your neck. Think about what happens when your expander ball sizes the neck back out after sizing. The neck gets a little bigger, and bounces back about a thou. Same thing when you seat a bullet. The neck expands to cal diameter and bounces back about a thou. Anything more is just over working the necks and creating unnecessarily high seating pressures forcing your bullets to expand your necks.

Makes sense. Thanks.