Neck Sizing for 20 Practical with Redding Bushing

[300meter]

I am necking down 223 cases, LC 05, for my 20 Practical project. If I do this in one step with a .231 bushing, the neck actually measures .227. If I use a two step process, .236 then 231, the neck measures .231.

Can someone explain why this occurs? Thanks.

 

[CatShooter]

I am necking down 223 cases, LC 05, for my 20 Practical project. If I do this in one step with a .231 bushing, the neck actually measures .227. If I use a two step process, .236 then 231, the neck measures .231.

Can someone explain why this occurs? Thanks.

Yes...

If the bushing is just a little smaller, the neck will flow into it and wind up the same dia or maybe 1 thou over.

But if the bushing is much smaller, then the neck starts following the feed ramp in the bushing and becomes a slight cone... as it keeps going into the bushing, it overshoots the the inner bore and "keeps on going", so it winds up smaller.

This happened to me yesterday... a .267 bushing with a .276 neck gave me a 263 neck when sized - but with a 271 bushing, I got a 270 neck.

I first ran into this with a 300WM 1,000 match rifle. The necks came out smaller than the bushing,the bushing would rattle on the sized neck), so I called Pat Ryan at Redding and told him about it... he said it was impossible, and I said go try it - he called me back 30 minutes later and said, "I'll be damned!"
The next catalogue, there was something written in it.

From the Redding material:

It has come to our attention through customer calls and our own use of the bushing style sizing dies that in certain instances, a given neck sizing bushing will produce a case neck diameter that can be several thousandths of an inch smaller than the actual diameter of the bushing. This idiosyncrasy occurs when the neck diameter of the fired case is a great deal larger than the diameter of the neck sizing bushing, such as occurs when factory chambers are on the large side of the tolerance range and the brass is on the thin side. Typically, we have not noticed any problems until the case neck is reduced more than 0.008-0.010".

Solutions include, increasing bushing diameter to compensate and/or the use of a size button. Reducing the neck diameter in two smaller steps by using an intermediate diameter bushing will also help. More concentric necks will also result using this method, as the case necks are stressed less during sizing. Don't forget to properly chamfer the inside and outside of the case mouths and apply a light coating of lubricant to the case necks before sizing.



Anytime you have to neck size a very large difference, do it in steps, because there is another problem that is not as apparent.

That is, when the neck is forced into a very small bushing, it will often size off center.

With my rifle yesterday,the fired cases are really nice with a neck/body run out of 0.0003". But when sized with the 267 bushing the run out became 0.011 - it was so bad that I could see it without a magnifier.

When the bushing was changed to the .271, the sized run out was 0.0006"


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[300meter]

Thanks for the advice and all the information. I understand now why the problem occured and the solution.