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proper amount of neck tension

 
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  #1  
Old 09-01-2013, 08:12 PM
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proper amount of neck tension

I've done some searches and can't find the answer to this question.

I'm loading for a 300 win mag and a 270 win with Norma brass and RCBS FL dies. The expander ball measures .3050" for the 300. I'm measuring neck tension by measuring the case mouth before and after seating the bullet. I'm getting .0020 to .0025 on both once fired brass and brass that has been fired 14 times and annealed 3 times. My gunsmith says that for my bolt action hunting rifle I need .004 to .005 to hold the bullet in place against accidental jars.

What do y'all think is the proper amount of neck tension???

Thanks.

Last edited by dmax1800; 09-01-2013 at 09:24 PM.
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  #2  
Old 09-02-2013, 05:39 AM
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Re: proper amount of neck tension

Most of the RCBS dies I bothered to measure yielded a .003" for difference between sized and loaded. Many handloaders will use .002" which can be done with a Redding S bushing sizer die. Some even use .001" or less but that is ammo not meant for a magazine.

I can't imagine wanting to go tighter than .003" for tension unless the rifle had recoil so severe that the rounds in the magazine experienced bullet setback. At that point a crimp is the more common solution rather than more neck tension.

I have read more than once that high neck tension could lead to misalignment of bullet causing poor accuracy.
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Old 09-02-2013, 07:02 AM
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Re: proper amount of neck tension

I am a firm believer that no cartridge requires any more neck tension than .002", even heavy kickers.
On my comp rifles and some of my very accurate hunting rifles I run .0015" neck tension , this includes my 338WinMag, never had any bullet setback during recoil and they're not crimped. The most important factor, especially with the 300WinMag, is that the neck tension is consistent across all cases. I anneal every other shot with my 300, but this is a target rifle, in my hunting rifle I only anneal whenever the brass needs trimming.

Even my 375 Weatherby and 416Rigby only get .002" neck tension, the Rigby gets a crimp but the 375 doesn't.
As a side note, a few years ago I bought some old Kynoch 416Rigby ammo, not sure of it's age at the time, but the ONLY thing holding the bullets in the necks was the case mouth where it had been rolled into the cannelure! I pulled them all, resized the necks and reseated the pills, and they shot quite well.

Cheers.
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Old 09-02-2013, 09:25 AM
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Re: proper amount of neck tension

Quote:
Originally Posted by dmax1800 View Post
My gunsmith says that for my bolt action hunting rifle I need .004 to .005 to hold the bullet in place against accidental jars.
Your gunsmith doesn't know what he's talking about, and I wouldn't be surprised if he's making more than that up as he goes..

For one, you cannot produce more than ~3thou of tension, regardless of sizing. That is all necks will spring back. Even very thick & hard necks.
When you size necks down more than this, bullet seating(with excess seating forces) will just size the necks back up, and the same spring back(as you would have without the oversizing) grips the bullet.

Necks won't ever spring back 4-5thou.

And when someone suggests that annealing will increase your tension, go ahead and tell them they don't know what they're talkin about. Annealing reduces springback, which is all that holds a bullet.
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Old 09-02-2013, 11:51 AM
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Re: proper amount of neck tension

I'm wondering of the obvious was missed.

Is it .002 on radius or diameter.

Example: all my 30 cals have an internal neck diameter after sizing that is .304. To me this is a .002 per 'side' neck tension. I check this often as it is not something I want varying much.

Your gunsmith may mean exactly as my example shows. An internal diameter .004 or .005 less than bullet diameter. For general loading, my instructor/mentor, reading and practice leads me to that standard measure.

For special forms of shooting, a neck internal diameter after sizing that is as 'low' as .002 less than the bullet diameter seems to work for some. Usually described around the same prose as 'tight' necks and 'match' chambers where neck turning is required.
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Old 09-02-2013, 12:12 PM
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Re: proper amount of neck tension

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Originally Posted by jfseaman View Post
Is it .002 on radius or diameter.
Its .002 diameter. I measure the diameter of the case mouth before and after seating the bullet. The difference is usually .0020 or .0025. Still no where near the .004 to .005 that he is talking about.
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Old 09-02-2013, 12:19 PM
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Re: proper amount of neck tension

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Originally Posted by Mikecr View Post
And when someone suggests that annealing will increase your tension, go ahead and tell them they don't know what they're talkin about. Annealing reduces springback, which is all that holds a bullet.
This statements needs to be further clarified Mike. I agree with you, but it also needs to be noted that when using a bushing die, and only down sizing .002 after a few firings the brass hardens and neck tension will be lost from added spring back. The cure is to either drop down in bushing size or anneal the brass to return it to it's original softer state.

My first hand example is this: 338 LM in Lapua brass. Great bullet hold with a .366 bushing. After 4 firings some of the bullets were loose. This indicated loss of neck tension as well as inconsistent neck tension. I dropped to a .365 bushing and they were all tight again. At this point I bought my first annealing machine and annealed this same brass. I returned to using the .366 bushing and all was tight again.

The problem I seen with dropping a bushing size was that not all cases needed the smaller bushing. This was proof to me that I indeed had inconsistent neck tension. I find that annealing more often keeps all the necks at the same hardness and allows me to run the lighter tension I desire and still hold all the bullets the same.

Jeff
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