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Pressure change on FLR vs neck sized
Discussion regarding the reloading of ammunition and tuning of loads for accuracy
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dakota1
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PostPosted: Wed Aug 29, 2007 2:28 pm    Post subject: Pressure change on FLR vs neck sized Reply with quote

I have always FLR my brass. I do not have a particular reason to do so, except those are the dies that I have. I have worked up my loads, many years ago. I have worked them up looking for pressure signs with a FLR case.

If I change to neck sizing, could/would there be a pressure change, due to the shoulder not having an expansion area in the chamber? Should loads be re-done for pressure signs?

If the pressure changes, then would the pressure change with each reload, since the shoulder is potentially being moved closer to the chamber wall, and changing the expansion space for the shoulder?

Thanks for any info.
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chambered221
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PostPosted: Wed Aug 29, 2007 3:47 pm    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

There will with out a dout be a pressure change from going from FLR to Neck sizing only. How much of a change cannot be predicted. As with any componets change, you should back off and work up looking for pressure signs. In your situation you didn't change a component but you are changing it's interior dimenssions by only neck sizing. It is this interior volume change that leads to the pressure change, not the shoulder having less room to expand. As far as a change with each reload, I've never noticed a pressure change in mine nor ever heard anyone speak of it.
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Handloader
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PostPosted: Wed Aug 29, 2007 9:51 pm    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

The only testing I have done is with a 270 Win, comparing FL with neck sizing, using a piezo strain gauge. No increase in pressure was detectable in a string of ten cases each. Allow that the resistance to brass expansion at peak pressure is slight as the purpose of the brass, in essence, is to simply seal the chamber and direct the pressure toward the mouth of the case.

Some minor and insignificant pressure change could result from using a very soft brass as opposed to a harder brass, but, a change in primers, powder lot or seating depth will have a far more detectable effect. We have recorded as much as a 9,250psi difference in simply using different lots of the same powder and nearly 5,000psi from switching primers.

The point can be made, however, for partial full length sizing. IOW, size the case enough for easy chambering but not enough to cause repeated set back of the shoulder. This will prolong case life and lessen the tendency of the brass to grow. Multiple full length resizing can prematurely weaken the case head and lead to case head separation in chambers that are on the loose side as the brass will flow forward. Case head separation is usually more common with cases that headspace on the rim, typically lever actions. That is due to oversizing the brass as well as lever actions having more give or stretching under pressure. Similarly, belted magnums should be sized to headspace not solely on the belt, but, more on the shoulder for maximum brass life.
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Deleted_User_2665
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PostPosted: Thu Aug 30, 2007 4:46 am    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

Handloader wrote:

The point can be made, however, for partial full length sizing. IOW, size the case enough for easy chambering but not enough to cause repeated set back of the shoulder. This will prolong case life and lessen the tendency of the brass to grow.

IMO...that's the only way to go, for reasons stated.
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dakota1
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PostPosted: Thu Aug 30, 2007 7:08 am    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

How is partial full length resizing done?
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Deleted_User_2665
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PostPosted: Thu Aug 30, 2007 7:55 am    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

Just a very slight bump of the shoulder, a thousandth or two, and minimal contact with the case body.

It's basically neck sizing with a FL die and a slight truing of the case body as a side benefit.

As Handloader said it's easier on the brass as brass work hardens and becomes brittle the more it's moved or reshaped....

Giving the shoulder that slight bump and allowing the case to basically be "checked" for trueness still gives you certainty with regards to chambering issues.
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Handloader
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PostPosted: Thu Aug 30, 2007 8:56 am    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

By way of addendeum, I should mention that variations in weight by brand and, in some cases, lot of brass can, also, have a pressure effect. For purposes of load workup and reloading, keeping brass standardized is important.
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dakota1
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PostPosted: Thu Aug 30, 2007 11:44 am    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

I will be using new brass, from the same lot.

I understand the concept from wildswalker, but what is the actual technique? How is the die adjusted to get the partial resizing effect? Do you screw the die down until it rests on the shoulder of the spent case, and adjust the die down, continuing to check with a caliper for shoulder movement?

This is new to me, details would great.

Thanks.
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skb2706
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PostPosted: Thu Aug 30, 2007 1:32 pm    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

dakota1 wrote:
I have always FLR my brass. I do not have a particular reason to do so, except those are the dies that I have. I have worked up my loads, many years ago. I have worked them up looking for pressure signs with a FLR case.

If I change to neck sizing, could/would there be a pressure change, due to the shoulder not having an expansion area in the chamber? Should loads be re-done for pressure signs?

If the pressure changes, then would the pressure change with each reload, since the shoulder is potentially being moved closer to the chamber wall, and changing the expansion space for the shoulder?

Thanks for any info.

By the nature of neck sizing the case you will load actually will have a greater volume than a case that is full length sized. This would reduce pressure as opposed to increasing it. True neck sizing can normally only be done a few times before the cases will require you set back the shoulder anyway. Gets you back to the partial sizing to get them to chamber.
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chambered221
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PostPosted: Thu Aug 30, 2007 5:30 pm    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

Handloader, I,m glad to of finaly come across someone who actually has a strain gauge. It's a tool that alot of us would love to have. I'm surprised that you found no pressure drop off in the .270 when comparing FLR to neck sizing only. ( please understand I'm not disputing your findings) My past experiences has shown velocity losses of over 100fps. by going to neck sizing.(via chronogragh) I've always concidered this a case volume issue. The 222 Remington that this occured in had a chamber that was rather large and brass life was very short. Sad For these reasons I started using a neck sizing die. Any thoughts or comments on this would be greatly welcomed. Very Happy
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Handloader
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PostPosted: Thu Aug 30, 2007 11:10 pm    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

chambered221: thanks for the post and observations. An accepted self criticism of my testing is that it involved but ten rounds of FL and 10 rounds of neck sized and only in one chambering, the 270 Win. To really have a better or more valid position, one should test numerous chamberings and variables before asserting some conclusion. Mea culpa.

I suspect that, in the long run, the issue may be somewhat academic at best and that other factors of handloading be more critical. What is apparent is that if we work up loads in a progressive manner and in adherence to proper techiques, excessive pressure (from whatever source) can be avoided. And should be.

As much as changes in components can vary pressure with the same load, too be aware that variation in temperature can be a significant factor in changing pressure, sometimes with unexpected and unfortunate results. Max loads may be OK, but, only at or lower than the temperature in which they were developed. In Arizona, this can be a huge factor. Loads developed at 65 degrees in the winter can be destructive if outside temp soars to 100+. Many handloaders have found that Hodgdon Extreme Powders lessens velocity variation related to temperature; evenso, it is still a factor for consideration.

While I have done some very high pressure workups on the experimental side (we were attempting to assess the failure pressure of various actions and components), for my own use handloads are typically considerably below max SAAMI as I value the longevity of brass, firearm and your humble handloader, me. Ten fingers still.
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steve4102
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PostPosted: Fri Aug 31, 2007 5:24 am    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

dakota1 wrote:

I understand the concept from wildswalker, but what is the actual technique? How is the die adjusted to get the partial resizing effect? This is new to me, details would great.

Thanks.

Partial Full Length Sizing means different things to different people. Some feel that PFL is trying to size only the neck with a Full Length Die and others think PFL is FL sizing the brass so there is a slight "Crush" fit when a round is chambered. When I use the term "Partial Full Length Sizing" I am refering to a slight crush fit.
Here is a detailed explanation on how to set up your FL dies for PFL sizing. Once you have your die set up for a slight crush fit you can then screw the die in just a bit to set the shoulder back a few thousands. Not a few thousands of a fired round, but a few thousands of the actual dimentions of your chamber.


1. Put the Shell Holder in the press and raise the ram.
2. Screw the Full Length(FL) Die into the press so it is about a "nickle's thickness" above the Shell Holder.
3. Lube a "Fired" case (walls and inside the neck) and squash it.
4. Remove the Lube and try closing the bolt on it in the chamber.
5. If the bolt closes with no resistance, screw the FL Die into the press about 1/8-1/4 turn and repeat steps 3 & 4
.6. As you feel the resistance begin, slow down how much you screw the FL Die into the press so you are at about 1/16 of a turn, or "Fine Tuning". At some point you will not be able to close the bolt and you are extremely close to having the FL Die in the proper position.
NOTE: The reason for this is because the FL Die has begun Resizing the Case-walls down to the Pressure Ring. As it does so, the Case-body lengthens slightly which in turn moves the Case-shoulder slightly forward. Then as the "Fine Tuning" continues the Case-shoulder makes contact with the FL Die and is moved slightly reward(or slightly shortens the Case-head to Case-shoulder dimension).
7. Stop when there is a slight bit of resistance when closing the bolt on the empty case. You now have a "slight crush fit" for the case in that specific chamber, or Zero Headspace.
8. Once you get it where you want it, take some masking tape or a black marker and put a Witness Mark where the FL Die Lock Ring is positioned to hold the FL Die in this position. Loosen the FL Die and return the Lock Ring to align with the Witness Mark and sung up the Set-Screw.Screw the FL Die back into the press and try squashing another case. It should have the same resistance as the previous one. If not, you need to re-adjust the Lock Ring so it does. But you are extremely close to where you want it, so make very small changes at this point.Occasionally check the fit of the cases in the chamber, say every 5th firing just to make sure nothing has slipped. Checking more often won't hurt anything and give you confidence that the Set-Up is still proper.You have now Set-Up the FL Die to P-FLR and will have the very best opportunity at having long case life and the very best accuracy possible.
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dakota1
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PostPosted: Fri Aug 31, 2007 7:06 am    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

steve4102,
Thank you for the detail on the PFL resizing.

Thank you all for your input on the pressure changes.
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dakota1
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PostPosted: Fri Aug 31, 2007 10:01 am    Post subject: Re: Pressure change on FLR vs neck sized Reply with quote

Once I have achieved a "crush fit" by doing a PFL resize, will measuring from the base of the cartridge (head) to the datum line (mid shoulder) give me the the chamber dimensions. Will that be the same as the headspace for that particular chamber?
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