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Resizing the casing neck

Over the last several months I have started to reload shells for my 300 WSM.  Finding a good overall oad was quite a chore, but I now have a good and accurate load.

That said, it seems to me that when I use new casings, my groupings are better than those that have already been shot.  Does any one else see this?  I resize and reset casing OAL each time I reload them, but I do not resize the neck.  Does anyone do this.  Do you think this could be the difference in accuracy?  

What do you use to resize the neck of a casing?

Thanks for the help.

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You are resizing the neck or

You are resizing the neck or else you would never get the bullet o stay in the brass.  But you are not resizing the shoulder. 

Here is the way that I do it.

Place your full-length loading die into your press and adjust it to where it is a half a turn from contacting the shell holder with the ram in the upward posistion and leave the locking ring loose.  Then take a case that has been fired in your rifle so that it fits in the chamber without sizeing it and lubercate it.  Then run it through the full-length die.  Remove the case and clean the lube off of it and try it in your rifle.  The odds are that the die sized the case body and moved the shoulder a little bit forward.  If this is the case the action will not close very easy on the empty case.  If it chambers easily you will need to back the die off a little bit more and start over with a different fired case.  When you have a case tht is resistant or doesn't want to chamber then you can start to screw the die down about a hours length of movement.  So if your die is set at 3 O clock tighten it down to 4 O clock. 

You then want to repeat this process of lube, running it into the die, cleaning, and running it into your rifle until the case chambers easily but you can still feel it chambering.  If you don't feel the case going into the chamber then you'll need to back the die off and start over with another case.

This way you should have a perfectly sized case for your rifle.  I would even do this to the brand new brass that you have. 

Also unless you trim your once fired cases before you reload them to a standard length you may have a little bit more case length with your once fired cases than new one.  That along with getting a neck turning tool to make sure that all the necks are of the same thickness will all help with accuracy out of a rifle. 

CVC
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Critter that is interesting. 

Critter that is interesting.  It is not a step I follow but I think I will try it as it seems like it will provide for a custom fit. 

Don Fischer's picture
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That is called "particial

That is called "particial re-sizing" and unless you are using a belted case, your not, or you have a head space problem I doubt it is of real value. First off a once fired case will re-chamber into your rifle even parcitial sized. So I doubt any real advantage to it. But if you have a headspace problem, you can adjust it out with particial sizing. Follow the directions above. If you were using a belted case it would work well also. The reason being chambers on them are notoriously sloppy as the case headspaces on the belt rather than the shoulder. By particial sizing them you in effect move the headspace point to the shoulder of the case. That goes a long way in eliminating case head seperation. If you are experiencing case head saperation in your cases, particial re-sizing will not fix the problem but will adjust it out. You'd still have it with factory cases.

About a year or so ago I did the particial re-sizing with my 243 just to see where I really was. First thing you'd need to do is particial size a few times so that the fired case when particial sized again will not chamber. At that point you can make the case fit your chamber exactly, but only for a round or two it your lucky. I did just that and then did as above except I took the die down with a feeler guage till the case would chamber, with no rubbing. What I ended up with was a die backed off the shell holder .001"! My conclusion is that particial sizing serves no value other than what I spoke of above.

As pointed out above, you cannot re-size the case without resizing the neck. In fact you cannot re-size all of the neck and bump the shoulder without re-sizing the whole case unless you do have to much headspace. The factory new case will meet SAMI specs. So will the re-sized case. Why you are experiencing this might be that what is happening is some of the new cases are at max length. You fire it one time then re-size it and you drag the neck a bit out farther than it should be. It will chamber but the end of the neck will hold the bullet tighter than befor, increasing pressure a bit. Take your once fired cases after re-sizing and measure them. Trim all of them to the min trim length.

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