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REAL differences in sizing methods?

 
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  #1  
Old 04-21-2009, 09:34 AM
tlk tlk is offline
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REAL differences in sizing methods?

Have been looking at old posts and have a question:

If you have to FL size every so often and this does not hurt accuracy vs neck only sizing, is it true that the only reason for neck only sizing is to not work the brass excessively? In other words, once you get the dimensions of the chamber, is it basically true that one method is not inherently more accurate than the other?

For example: if you fireform brass and show no difference in accruacy vs neck sizing, then neck size the next few reloads, then FL size, all with no real change in POI, what advantages are there other than possibly extanding case life? Am I missing an important point?

Given the price of Lapua brass, I can completely understand the case life issue...

Thanks.
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Old 04-21-2009, 06:27 PM
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Re: REAL differences in sizing methods?

A few factors in this:
Your cartridge
Your chamber dimensions
Your die match(to the chamber)
Your brass match(")
Your load
Your brass variance in thickness
The amount of barrel steel supporting the chamber walls

Ideally you size as little as possible for reasonable fit and ejection(bolt effort, headspace, brass life, low runout).
In this quest, the factors mentioned will lead to what you can get away with -with equal results.

Many BR shooters go right ahead and FL size each time. But their conditions are well controlled. If you do this with random brass out of a range bucket and a sloppy factory chamber, your results will not be the same.
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Old 04-21-2009, 08:50 PM
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Re: REAL differences in sizing methods?

Most of the times in these threads there is a difference of opinions directly related to the actual definitions of the different types of sizing. Since there is no definition as written somewhere (at least that I have seen), perhaps we could agree on terms:

Partial Neck Sizing (PNS) - sizing part of the neck and not sizing the case body or contacting the shoulder. You can do this with a FL die by backing the die up 3/4 turn or more.

Neck Sizing (NS) - sizing all the case neck but not sizing the case body or pushing the shoulder back. This takes a dedicated neck sizing die, either with an expander, bushing or collet type.

Partial Full Length Resizing (PFLR) - sizing all the neck, sizing the case body and pushing the shoulder back far enough so it does not bind with a crush fit, but still maintaining a very slight contact at the shoulder. This can be done with a FL die usually by adjusting the die in an additional ~1/8 turn past where the die bottom hits the shell holder. Or it can be done with a body die after neck sizing. Or it can be done with one of the new bump dies.

Full Length Resizing (FLR) - sizing all the neck, sizing the case body and pushing the shoulder back far enough so there is no contact between the chamber shoulder and case shoulder.


As far as which one is best, IMO the most important thing in accuracy is consistancy. With PNS or NS the case dimensions are in flux in that the shoulder is expanding more and more forward until it binds at the shoulder, usually in 3 or 4 firings. So the case dimensions are not exactly the same, very close but still not exactly the same. With FL resizing you can set the shoulder at exactly the same place everytime but the case has some slop in the chamber and that could cause a problem. With PFLR you can set all the dimensions exactly the same everytime and the case will be held in stasis between the bolt face and the chamber shoulder in approx the very same position everytime.

There are a lot of other factors you need to control also: bullet grip, runout, seating depth, powder selection, bullet selection, etc. But IMO if you PFLR to the exact same dimensions everytime you take one variable out of the equation. Then you can work on all the rest.
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Old 04-22-2009, 11:38 AM
tlk tlk is offline
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Re: REAL differences in sizing methods?

Here is what I hear you both telling me:

I have a SAAMI spec chamber, and in order to keep everything consistent I probably should NOT be f/l resizing, which will allow the brass to take up the dimensional "slop" of the chamber so that if runout and other factors are controlled, the bullet should be aligned to the bore. While f/l sizing may give me concentric ammunition, it may not give the best accuracy due to the free space left in the chamber (bullet may not be in alignment with the bore).

Woods, tying in another answer you gave me with this thread, I take it you mean that post fireforming, partial f/l sizing may be the route to take because it holds the brass at approx. the datum point (chamber shoulder, almost a slight crush fit) and the case head/rim (bolt face). The case body can expand, but most everything else is controlled because of the "bookending" type of effect accomplished with PFLS.

Thanks for the help. Let me know if my conclusions need correction.
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Old 04-22-2009, 02:12 PM
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Re: REAL differences in sizing methods?

Well stated.
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Old 04-22-2009, 02:45 PM
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Re: REAL differences in sizing methods?

Quote:
The diameter at the shoulder is still reduced. You can not neck size with any full length sizing die. The taper of the case prevents that. You can partially size the neck and case with a full length die..

One problem that can occur when you try and neck size with a full length die by backing it off a bit, is sometimes when the neck and shoulder diameter are being sized, the shoulder itself will bulge forward ever so slightly. When this happens the case will feel a bit hard to close the bolt on... This almost microscopic bulging of the shoulder does not occur when using a neck sizing die which sizes only the neck diameter.

There is nothing wrong with full length sizing providing you do not push the shoulder back excessively from it's fire formed form.
Is from one of the recent BR central discussions on the same thing.

Now if the top BR shooters are FL sizing with extreme accuracy, what makes a partial NS or NS only all the time so desirable.

You are still resizing the body some on a FL die that is just unscrewed anway and possibly making it unchamberable.

Now what does this gain vs what does it risk in reality?

Obviously we are talking factory chamber which means factory barrel, so match grade accuracy is not a real consideration and no NS only or partical NS brass is going to give it.

Jury rigs normally give jury rigged results at the worst times. Either do it right with a proper sized FL die and properly adjusted or NS and then use a body die every 2-3x.

Gain is in reality more imaginary feel good vs anything actual. Yet you risk brass that will not smoothly chamber. Which IMO for hunting gun is not smart.

Unless you are using a shoulder bump gauge or Hornady shoulder comparator you do not have a clue how much you are bumping the shoulder back or where it even is in relationship to your chamber.

Now if you go about it slow and use brass that is reached the point of hard to chamber, you can use lamp/candle black and set the FL die up high. Slowly lower it 1/8 turn at a time until it just touches the shoulderand the case will smoothly chamber. That gives you the shoulder bump with minimum brass working and max case life.

Starting off adjusting your die to touch the shellholder is the directions that come with it, but not conducive for minimizing working the brass. You often times are pushing the shoulder back way too much. It will chamber easily and that is why the die mftr tells you to do it that way.

If you want to be that precise and use a factory die in a factory chamber, then do it right. Send your die to be honed to match your chamber by Jim Carstenson at JLC Precision. He can do necks and bodies. That way it will match your chamber.

A properly sized FL die does not overwork the brass and ensures consist neck tension and body diameter.

Now to further throw water on this, the necks are going to work harden no matter what you do and you are going to get inconsistent neck tension after 3-6 firings unless you anneal. No way around that. More groups are lost for neck tension issue than brass bodies overworked.

BH
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Old 04-22-2009, 04:02 PM
tlk tlk is offline
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Re: REAL differences in sizing methods?

Man, sometimes trying to learn off of you guys is like drinking from a fire hose. I have to read every post multiple times just to make sure I understood what you said. Where did I miss "longrange hunting 101"?

BountyHunter, SAAMI in my case does not mean a factory barrel. It means that I had no idea of the true differences between SAAMI and match chamberings when I ordered the barrel. Lesson learned. I have not one clue if it will shoot match grade, but there is no need to pay for something and never use it all.

BTW, aren't you and Woods saying the same thing - that it is better to fl size but keep the length of the case the same as the chamber (again, meaning bolt face to datum)?

Thanks.
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