Necking up vs necking down - Which is better?

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Necking up vs necking down - Which is better?

Post by sneaker » 12 Feb 2014, 9:59 am

Hi all,

Just as a theoretical example (with some imaginary cartridges for convenience...)

Say you needed ".300 Winchester" brass and couldn't get any, and had the option of either:

A) Necking up ".290 Winchester" brass or...

B) Necking down ".310 WInchester" brass...

Which would be better? If at all?

Pros/cons of going up vs down in neck size?

Is one preferable or are they much of a muchness?

Cheers.
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Re: Necking up vs necking down - Which is better?

Post by scrolllock » 12 Feb 2014, 12:05 pm

Ah yes, my two favourite calibres. The .290 and .310 Winchester :lol:
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Re: Necking up vs necking down - Which is better?

Post by Chronos » 12 Feb 2014, 1:23 pm

Let's use a real world example

I had a .308, sold it and kept 300 .308 cases. (.308 bullet)

Then I bought my 7-08 (.284 bullet) which is essentially a necked down .308

I full length sized the cases in the 7-08 die, I trimmed them to length for uniformity then skimmed the necks to ensure uniform neck tension. I've now been using these cases for a few years, no issues.

A mate used .260 cases and ran then through a 7-08 die, didn't neck turn just trimmed to a uniform length

I've heard of others using .243 brass in their 7-08

All these calibers share one case design, the 300 savage. Similar to the way the .270, .280 share the 30-06 case

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Re: Necking up vs necking down - Which is better?

Post by VICHunter » 12 Feb 2014, 2:20 pm

Both will work, with a few considerations... None of these are necessarily "problems" but depending on the performance you expect, or just maintaining best practices you may want to address them.


1) When necking down brass you're compressing more neck into less space, making the neck wall thicker.

The thicker neck may create an increase in neck tension on the bullet and give a different POI compared to factory brass.

Best practice would be to neck turn them like Chronos said so the neck walls are a consistent thickness. Once the necks are turned, for all intents and purposes you have 'factory' spec brass and it will be no different. It's not critical though.

Failing that, simply firing the cartridges will make the neck extend and thin, normalising the brass. With repeat firing and reloading the resized brass will just become part of the regular rotation of brass.


2) On the flip side, when necking up brass you're stretching the neck and it will thin. There would be no need to turn the necks and they'll already be more than thin enough. This too could result in a change in POI, compared to factory brass, but isn't an immediate concern.

The only real concern with necking up is that you're starting off with less neck, so the brass won't last as long before failing. You'll end up with split necks sooner compared to factory or necked down brass. Again, not critical, you'll just get a bit less bang-for-your-buck on a shots-per-brass basis.


Turning the necks in option 1) would be ideal, but any of the above will work in a pinch.
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Re: Necking up vs necking down - Which is better?

Post by Norton » 12 Feb 2014, 9:10 pm

I dunno what calibres you've got, but if you've got the dies to try it, lube up a case or two and run them through your full length dies up and down a step if possible.

With close inspection you'll see the difference in the neck wall thickness. Necking down, nice thick walls. Necking up, they will often stretch so part of the neck is noticeably thinner. Only a fraction of a mm, but noticeable upon inspection.

Still good to shoot, just the thin part of the neck will likely give out first.
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Re: Necking up vs necking down - Which is better?

Post by lole » 12 Feb 2014, 9:36 pm

Norton wrote:Necking up, they will often stretch so part of the neck is noticeably thinner. Only a fraction of a mm, but noticeable upon inspection.


If you go up enough... Going up from something like 7mm to 7.62mm I don't reckon you can tell the difference by eye.

Going from something like .243 to .308 though you're right.
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Re: Necking up vs necking down - Which is better?

Post by Vati » 12 Feb 2014, 9:40 pm

I can tell, I'm that good 8-)
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Re: Necking up vs necking down - Which is better?

Post by Bourt » 13 Feb 2014, 4:37 pm

I'm going to go ahead and call you a liar, Vati :P
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Re: Necking up vs necking down - Which is better?

Post by sneaker » 12 Mar 2014, 3:07 pm

Hi all,

Thanks for the replies. Neck turning is something I want to give a go too so I reckon the necking down and turning is the process to use.

This is for a future project though so getting ahead of myself.

Something for me to do down the road :)
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