Purpose behind different neck lengths

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Purpose behind different neck lengths

Post by VICHunter » 29 Mar 2018, 9:44 am

A random bit of curiosity popped into my head today while doing some reloading, that is, what's the purpose of different neck lengths in cartridges.

As an example, the .308 Win, 7mm Weatherby Magnum and 30-06 Springfield all fire similar projectiles.

Neck lengths for the cartridges are .300", 0.321" and 0.385" respectively.

When designing a cartridge, why would one decide to extend the neck length?
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Re: Purpose behind different neck lengths

Post by sungazer » 29 Mar 2018, 11:31 am

Perhaps for sealing the chamber when they are fired.? :unknown:
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Re: Purpose behind different neck lengths

Post by Oldbloke » 29 Mar 2018, 12:15 pm

Could it be relative to the cartridge powder capacity for some reason? E.g. more powder more grip required.
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Re: Purpose behind different neck lengths

Post by lole » 29 Mar 2018, 12:35 pm

Maybe the guys at Springfield army base where compensating and made a new cartridge so they felt like they had a long...... neck :lol:
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Re: Purpose behind different neck lengths

Post by Apollo » 29 Mar 2018, 6:47 pm

Oldbloke wrote:Could it be relative to the cartridge powder capacity for some reason? E.g. more powder more grip required.


Hmm, .223 vis .222 and the .222 has almost the same powder capacity but near twice the neck length..??

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Re: Purpose behind different neck lengths

Post by sungazer » 29 Mar 2018, 7:03 pm

It does have something to do with the bullets they intend to shoot. Of course later other come with lots of other bullets that will work in the case. Normally a inventor I would imagine would be looking to hold the bullet as concentric to the bore as possible. A few reasons I honestly have no clue. Perhaps you could get correspondence from an inventor or modifier.
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Re: Purpose behind different neck lengths

Post by Stix » 29 Mar 2018, 7:32 pm

Well its a little daunting putting up an answer when Apollo has assumed the role of professor in chief assignment marker...but...
My guess from my most basic knowledge would be that its (obviously) cartridge specific & prob got something to do with the lede/lead (not sure of spelling--pronounced "leed"--the kinda free-bore area forward of the neck), as i underatand that is effectively part of the combustion chamber & effectively part of the cartridge design.
I guess the guys making/designing/doing the r&d check that stuff & go with what they deem is the most efficient for the said cartridge brief.
So a cartridge with a smaller/shorter lead volume can get away with a shorter neck to hold the bullet as part of its initial combustion chamber is forward of the case.
If it had a longer neck it would block this area off & increase pressures...hence trimming/max length of brass for any given cartridge...??? ?...
Ah hell i dunno :x .... :crazy:
Thats my guess...

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Re: Purpose behind different neck lengths

Post by marksman » 29 Mar 2018, 8:55 pm

VICHunter wrote:
When designing a cartridge, why would one decide to extend the neck length?


neck length is driven by several things, the need to grip the bullet and the flexibility to use multiple bullet weights,
it was believed you got better accuracy from a longer neck as a longer neck would hold the bullet straighter as well as less throat erosion
when you start blowing out cases eg the dasher vs the br you see the short versus long neck argument is IMO outdated nonsense :crazy:
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Re: Purpose behind different neck lengths

Post by sungazer » 30 Mar 2018, 8:20 am

Your probably right marksman. I mean the neck does have some important jobs to do. But I wonder how many qualitative tests and test based research has been done n developing a lot of cases. for sure some have been done just for egos sake a lot of the (wildcats). Then there has been the copys save a couple of mm just so a nation could have there own. some times that was sensibly driven so they could use the enemies ammunition and not vise versa.
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Re: Purpose behind different neck lengths

Post by straightshooter » 30 Mar 2018, 2:54 pm

Once upon a time (I will leave out the long ago and far away bits) it was the considered opinion of many ballistician cartridge designers that it was highly desirable for the 'focus' of the burning powder to be at least one caliber inside the neck. (I use the word focus because I can't remember the proper term.)
If you draw two imaginary lines, being extensions of the inside shoulder, where they intersect is the 'focus'.
It was important to have this point, being the concentrated and hottest portion of the burning powder, inside the disposable brass case so as to minimize throat erosion.
In modern times this idea seems to have gone the way of the dodo.
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