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Even neck tension

 
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  #1  
Old 04-13-2011, 07:03 PM
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Join Date: Feb 2011
Posts: 26
Even neck tension

I am loading for 308 and have a Sinclair case length trimmer and a Forster that I use only for turning the outside of the neck. The problem is I know I do not have even neck tension even if the outside is concentric because the pilot that goes into the brass fits some brass and is very difficult to fit inside other necks.

I tried aForster inside neck reamer but it is supposed to be used before brass resizing and it does not engage the neck at all then. If I use the reamer after resizing, it cuts too much out.

I believe Sinclair and K+M make mandrels to make the neck inside dimension uniform. I cannot find instructions as to how they work. Do I need to get one of these and by pushing the brass out, then trim on the outside only? Do I need to get a custom sized inside reamer to use on my Forster and use it after resizing?

The bottom line is even if I have perfect concentric outside neck dimensions ( I do have a dial gauge to measure this) I know my neck tension is variable when the collet that goes into the neck while turning the outside fits with variable tension.

I don't know what to do. Please help
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  #2  
Old 04-13-2011, 11:26 PM
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Join Date: Jan 2009
Posts: 196
Re: Even neck tension

I use the Sinclair expander mandrel and the undersized turning mandrel to turn the necks on my brass, this gives you a size-able brass with neck tension. I anneal my brass after every firing this makes a great big difference with neck tension, trust me learn to anneal brass and your seating depth and neck tension problems will go away.
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  #3  
Old 04-14-2011, 04:58 AM
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Location: PA
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Re: Even neck tension

Always use an expander before turning necks. Do not use an inside neck reamer, ever. I have the Forster trimmer-turner also. Its OK for trimming but does not do a good job of neck turning. I have gone to K&M neck turners and love them. Once set, I dedicate that turner for that rifle only. Lightly lube the mandrel each time you turn.

I assume your 308 fits a factory chamber. If so, all you need to do is very lightly skim the case neck, to create an even thickness all around. Measure the brass thickness on several places in the neck with a tubing mic.
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  #4  
Old 04-14-2011, 08:33 AM
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Location: Sedalia, MO
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Re: Even neck tension

itrshooter,

This is what expander balls are all about; uniform neck tension. It is also exactly what you'll accomplish by using an expander mandrel. In use, you simply run the case mouth up onto the mandrel, and it sizes it from the inside. This negaes any variation in neck wall thickness, which cause uneven tension if you've sized them only form the outside, i.e., using a bushing die without an expander ball.

I like bushing dies, since it allows me to control neck tension to precisely what I want. Many will advise that these also allow you to size without using an expander ball, which is true . . . sort of. Expander balls can cause all sorts of problems, but most of these relate to the use of dies which size the necks down far to tightly, and then brutally drag the expander back through the undersized nect, with bad results. Choose a bushing that sizes the necks down to the point where the expander just kissses the necks during their passage back out, and you'll get uniform neck tension while avoiding the problems normally associated with them (the expander balls).
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Kevin Thomas
Lapua USA
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  #5  
Old 04-19-2011, 03:54 PM
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Join Date: Dec 2005
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Re: Even neck tension

Quote:
Originally Posted by Kevin Thomas View Post
Expander balls can cause all sorts of problems, but most of these relate to the use of dies which size the necks down far to tightly, and then brutally drag the expander back through the undersized nect, with bad results. Choose a bushing that sizes the necks down to the point where the expander just kissses the necks during their passage back out, and you'll get uniform neck tension while avoiding the problems normally associated with them (the expander balls).
Kevin's right about expander balls.

I got a bunch of .311 caliber expander balls then polished 'em down to .3080" up through .3090" in .0002" steps. Using several regular RCBS full length sizing dies with their necks lapped out to .332" to .338" in .001" steps, I could tackle all sorts of .308 Win. cases to hold 30 caliber match bullets ranging from .3082" to .3092" with the tension I wanted when case neck wall thickness for each lot/batch of cases had its own dimension. Used a die whos neck diameter was anywhere from 1 to 4 thousandths smaller than a loaded round's neck diameter with an expander ball to just barely "uniform" the case mouth diameter. Bullet runout using this process was under 2 thousandths; great for accuracy.

The key to this set of tools and their use is case mouths aren't sized down and expanded up more than necessary. Necks stay straighter and don't get work hardened and brittle. Cases last longer. .308 Win. cases could be reloaded several dozen times this way and never need their necks annealed.

Last edited by Bart B; 04-19-2011 at 03:57 PM.
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  #6  
Old 04-19-2011, 08:56 PM
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Join Date: Feb 2011
Posts: 26
Re: Even neck tension

Thanks for the advice. I ordered an annealer and now realize that I needed a mandrel to prepare the brass before I turned it. I ordered a 21st century neck turner and mandrel as I don't really like the Forster one.
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  #7  
Old 04-20-2011, 12:42 AM
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Join Date: Sep 2009
Posts: 158
Re: Even neck tension

Quote:
Originally Posted by Bart B View Post
Kevin's right about expander balls.

I got a bunch of .311 caliber expander balls then polished 'em down to .3080" up through .3090" in .0002" steps. Using several regular RCBS full length sizing dies with their necks lapped out to .332" to .338" in .001" steps, I could tackle all sorts of .308 Win. cases to hold 30 caliber match bullets ranging from .3082" to .3092" with the tension I wanted when case neck wall thickness for each lot/batch of cases had its own dimension. Used a die whos neck diameter was anywhere from 1 to 4 thousandths smaller than a loaded round's neck diameter with an expander ball to just barely "uniform" the case mouth diameter. Bullet runout using this process was under 2 thousandths; great for accuracy.

The key to this set of tools and their use is case mouths aren't sized down and expanded up more than necessary. Necks stay straighter and don't get work hardened and brittle. Cases last longer. .308 Win. cases could be reloaded several dozen times this way and never need their necks annealed.
Seems like a lot of messing around for the price of set of wilson dies and bushings? but it makes some sense.
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