REAL differences in sizing methods?

[tlk]

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.

 

[Mikecr]

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.

 

[woods]

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.

 

[tlk]

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.

 

[woods]

Well stated.

 

[BountyHunter]

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

 

[tlk]

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.

 

[BountyHunter]

Next time your rebarrel buy your own reamer (Dave Kiff at Pacific Tool and Guage) and get it minimum SAAMI. Factory still fits, just not real loose. Dave is good guy and can easily talk to you and get the right reamer for what you want.

Now if it is not factory chamber, go back to your smith and ask for copy of reamer drawing. at least dimensions off it at the base, shoulder width, datum line and neck diameter.

Maybe we agree, but definitely not on the partial NS and how to adjust a FL die. To in reality to do the PFNS you need to use expanding mandrel and neck back to larger caliber up . Then partially NS down, but use a NS die. That is how set up a false shoulder for fireforming also. Otherwise, you are not touching or close to anything as you have the normal brass shrinkage on firing expanding and shrinking and will still be at least .002 less than chamber neck.

Now if your die is honed to your chamber and if your FL die is adjusted correctly, you are going to auto center from the bolt face to the datam line anyway IF all you bumped the shoulder was .0015 or no more than .002. Plus your round will chamber. IMO just smarter and more reliable way to get there.

Nothing in flux, no variance and you have 100% reliability. IF your die was cut straight also (that is another issue) you have loads that normally will exceed your expectations. All other things equal.

Anyway just my opinion.

BH

 

[tlk]

BH, I will give them a call tomorrow and hopefully get that info. THAT would be great to have.

Thanks for the help.

 

[woods]

I suspect that we are again agreeing but not using the same definitions. I would bet a 100 dollar bill that if you asked the BR guys they would say something like

"Yeah, I FL resize but only set the shoulder back .001" or less"

which is what I tried to define PFLR as. I doubt they will be sizing so much to lose the "bookending" quality that tlk mentioned, but they will call it "Full Length Resizing".

As far as adjusting the die, let me quote from the RCBS instructions for a regular FL die

"Screw the full length sizer die into the press until the die touches the shell holder when the shell holder is brought up to the top of the press stroke. Be sure all play is removed from the press leverage system. To do at this, adjust the die as above, lower the shell holder AND SET THE DIE 1/8 TO 1/4 TURN FURTHER DOWN so the press cams over center. Set the large lock nut and you're ready to size."

For their Competition Dies it says the same thing, as it also does for their Gold Medal Dies instruction sheets.

I don't have the instruction for any other FL dies and don't use them myself. For me it is always a Lee Collet/Redding Body Die or a Redding Bushing Neck Sizer/Redding Body Die.

I have created false shoulders before and monitor springback continuously with pin gauges. Also push the shoulder back .0005" to .0015" for a very slight crush fit (bookending).

As far as springback on necks, I have 4 tight necked custom chamber guns and measure the outside diameter of the fired necks and have always gotten .001" or less springback

338RUM - once fired outside neck .365"
twice fired outside neck .3655"
three time fired outside neck .366"

280AI - once fired outside neck .312"
twice fired outside neck .3125"
three times fired outside neck .313"

6.5 rem mag - once fired outside neck .262"
twice fired outside neck .2625"
three times fired outside neck .263"

But this is off topic.

For me it "Bookend 'em and send 'em downrange!"

 

[tlk]

Hey now, something just clicked in my head. The reason for all of the fuss over the shoulder in this discussion is because if a partial full length resize is done the shoulder must closely match the chamber in order to get a proper alignment.

In other words, the shoulder is a "chamber within a chamber", so to speak. If the case body is not held in alignment by the chamber itself (i.e, the brass o.d. is close to/matches the chamber i.d.), then the case must be supported by the chamber shoulder and the bolt face in order for consistency to occur. In this instance you are actually using the shoulder as a guide/funnel/forcing cone of sorts to ensure the bullet is aligned with the bore, assuming everything else is good. The shoulder is being used to narrow down to a specific point in the center of the rifle bore - and anchor there for lack of a better term.

This also means that if the bolt face has not been trued then the best accuracy cannot be obtained because it is putting a leveraging effect on the case shoulder, neck and bullet (the case is being pushed off center by the amount of "non-true" in the boltface). In addtion, if the case has been shortened too much and the "bookending" does not occur, such as with standard resizing instructions, then the alignment of the entire case to the chamber is off because it is wallowing around/laying in the bottom of the rifle chamber (which is why the talk about so little (.001) off of the datum).

Makes sense to me, but is this correct? If so, some other things became clearer too.

 

[woods]

Absolutely. But again you have to get to the point where your case shoulder has expanded far enough to bind on the shoulder. If you just neck size that can take 3 or 4 firings. This is a set of measurements on a 30-06 that is typical:

Taken with Hornady Headspace Gauge and neck sized only
New case - 2.040"
Once fired - 2.0485"
Twice fired - 2.050"
3 times fired - 2.051" (slight crush fit)
4 times fired - 2.0515" (crush fit)

So using the same gauge and chambering the case as you size you can set the shoulder to 2.051" or 2.0505" for a little "bookending".

As Bounty Hunter said, you can also shorten the process by setting the FL or body die to size the case body and that will push the shoulder forward a little as it squeezes the case body smaller. IME that is only .001" to .0015", not enough to create a crush fit when sizing once fired cases, but you will be able to reach the shoulder sooner.

Another way to possibly help during the neck sizing phase is to leave part of the neck fire formed size

You can do this with some of the dies made to do it like the Forster bump die. You can also do it with the Lee Collet by placing a washer on top of the shell holder

Also with a FL die by Partial Neck Sizing described earlier.

IME, the best loadings come after 3 or 4 loadings when you anneal the necks and PFLR. Of course, all this depends upon the specific size of your chamber, the interior dimensions of your die and how hot you are loading.

YMMV

 

[tlk]

One more question, please . This one involves easy math using the numbers below.

Woods, are you saying that getting a case to 2.051" cannot be done on an unfired or once fired case with a FL sizing? Put another way, although I can speed up the process with FL sizing (die set to final dims desired), is my brass size quest still dependent upon firing; no amount of initial sizing in a die will get me to where I need to be without a shot being fired.

Here is why I say that: Using your data, I see that new brass is 2.040." If I F/L size as per BH's instructions the new dims will be approx. 2.041" to 2.0145" (adding your estimated length that method will add). Still not enough, so I have to shoot the brass. Then I get 2.0495" to 2.05". From here, F/L sizing (same method) gets me to 2.0505" to 2.051".

-------Summary------------
While the numbers are an estimation the general conclusion to be made here is that proper alignment with the bore/correct sizing to the chamber cannot be made without stretching the brass in a chamber via firing at LEAST once. No way around it - the rifle is being used as critical sizing die.
-------------------------------


I think I am shaky ground here with this reasoning. In particular, I am wondering if the NEW case will size correctly on a die that has been set to 0.001" of the datum line for my chamber (i.e., the stretch required for the case is too extreme (trying to get the case to stretch 0.011") and makes a poor/unsafe load). And - can you run the case through the f/l sizer multiple times to get the brass to the final dims or is it a waste of time?


Woods, I have taken your advice and ordered the Hornady headspace guage.


I wanted to thank you guys for this thread. It helped me figure out that we are dealing with a series of cylinders (barrel, chamber, case, bullet) and in order to keep multiple interacting cylinders in alignment we are dealing with measurements that must be perpindicular, parallel or a true cone relative to a centerline in the rifle bore. Everything in a chamber and ammunition must be one of these three. Geometry became useful again....

 

[woods]

Throw this into the mix.

You can not FL resize new brass, period....

IOW, new brass is so much smaller than your die dimensions that the die will not size the case body and the shoulder is so far back that you should not be able to set the die so that it contacts the shoulder at all. The most you can do to a new case is to resize the neck.

So, yes you are correct that some firing is necessary to fireform your case to your chamber before you can start dealing with these issues. Essentially if brass did not have springback then you could fire your case once and it would be the exact size of your chamber, however it would be hard to extract and remove from the chamber or the sizing die.