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Discussion Starter #1
Hello Fella's,

Sorry to start another thread on sizing dies. This is sort of a spin off on, "New Guy Questions on Die Set Up"

I'm not necessarily new to reloading but I'm forever learning. The man that taught me how to reload told me to set the sizing die by by screwing it down on until it makes contact with the shell holder. For years that has been good enough. I've been reading at various places about head spacing and sizing the brass so that the shoulders are pushed back by .002"from the chamber dimensions. In theory, this sounds good.

I'm reloading for a sportorized Mauser model 98 chambered for the .30-06. I've been using Nosler brass. I purchased a Sinclair bump gauge insert. http://http://www.sinclairintl.com/reloading-equipment/measuring-tools/bullet-comparators/sinclair-bump-gage-insert-prod35265.aspx. I'm using a digital caliper that measures out to 4 decimal places. I proceeded to zero my calipers by closing them down on top of the empty insert and zero the calipers in this position. I then proceeded to measure 17 of my fired cases.

The first time I measured the cases, I got the following results. 1.9535, 1.9540, 1.9545, 1.9545, 1.9545, 1.9545, 1.9555, 1.9550, 1.9555, 1.9550, 1.9535, 1.9575, 1.9555, 1.9555, 1.9555, 1.9565, and 1.9565. I was a bit frustrated by these results as I was a expecting the measurements to be a bit more consistent and I wasn't expecting to have such a large spread from the smallest to the largest. I thought about this for a moment and I thought maybe the primers are a bit high and they may be skewing my results. I proceeded to use my RCBS universal decapping die and removed all the spent primers and proceeded to recheck the lengths. I got the following results. 1.9545, 1.9540, 1.9535, 1.9540, 1.9545, 1.9540, 1.9535, 1.9530, 1.9525, 1.9520, 1.9525, 1.9535, 1.9525, 1.9525, 1.9525, 1.9525, and 1.9530. Again, not the kind of results I was hoping to find.

Why would I get these kind of results? Are calipers not capable of taking this fine of a measurement? Could it be that I'm just not capable of taking such a fine measurement with the tools that I'm trying to use? Is there a something wrong with the Sinclair bump gauge insert? Is there a better method taking this measurement? If I was to back my sizing die off by .002", what measurement would I subtract it from?

Is the spread of these measurements what one would expect? Could the difference be because of the temperature of the brass or maybe even the barrel when the rounds were fired?

Does the brass really conform to the exact dimensions of the chamber when it is fired? Isn't there some spring back even though it might be quite small? Would this spring back always be consistent from one piece of brass to the next?

As someone mentioned in the other thread, I'm beginning to think that maybe the best way to set up the sizing die is by trial and error checking for fit in the chamber of the rifle and making small adjustments to the die until this fit is proper for closing the bolt handle.

I kind of wish the man who taught me to reload was still alive today so that I could ask him what he thinks. Even though I know he knew what headspacing was, I know he never tried to measure it the way I have. Maybe he's looking down from heaven and laughing at what I'm trying to do. I miss him much.

I look forward to hearing your responses.
 

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I get the same minute results that you are getting. The only variable in my sizing is the brass itself. Each piece of brass will have a different rate of spring back, but it is within a tolerance. I size by my chamber dimensions, then check with a gauge. Some cases will be .001-.002 longer or shorter than the one previously sized. Even measuring fired cases before sizing you will see variations in length. There is no "perfect" brass, just get them as close as you can and eliminate as many human variables as you can.

I can set my die to size one particular case to .000 clearance, run 5 more pieces through the die and at least one will show some resistance when closing the bolt. When I want to shoot particularly small groups, after sizing I will gauge all cases and separate them. The longer cases I will reset the die in .001 increments and run them through again. Sometimes this works, sometimes not. Because of the brass tolerance, you will see many BR shooters use as few pieces of brass as possible, sometimes only one, and reload those pieces, or that one, at the bench. Using just one piece of brass eliminates another variable.

Allen
 

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1. You are expecting a bit much from your calipers unless you are a professional that uses them everyday. The 4th decimal place is worthless with your calipers. They simply do not permit that kind of precision.

2. Any variability in your sizing procedure can contribute to the variability that you see.

A. The amount of lube that you use and how consistently it is applied causes variation in the amount of sizing.

B. The speed that you size the case affects the case sizing. The slower the sizing the better.

C. Multiple sizing strokes reduces the variability. Adding dwell to the end of the sizing stroke gives the brass a little bit of time to creep to a more consistant location. So let the press ram dwell 3 to 4 seconds at the top of each stroke. Lower the press ram just enough to permit spinning the case about 120 degrees, size again slowly with 3 to 4 seconds dwell, then spin another 120 degrees and size again and allow to dwell again.
All of this will give the brass enough time and repeated cycles so that the brass will take on exactly the same dimensions for all pieces.

This also helps get rid of variations from once fired brass that comes from different rifles.

If you have any questions you can prove that your technique causes the variation very easily.
I found out by forming 100 .303 British cases to 6.5X53R Dutch brass. I measured each case with a Stoney Point after it was formed with the trim die.
I could tell when I did not use enough lube because the case would be a little longer. So I would size it again.
I could tell when I sized the case too fast or did not use a dwell.

Not only did I measure each and every case as it came off the press but I used my rifle with the bolt stripped to feel the length of each case.
I had set the form and trim die to give a very faint drag with the case shoulder against the chamber shoulder even those this is a rimmed case.
Any long case also gave heavy drag in my rifle when the bolt was closed and that also corresponded to a longer shoulder to head length when measured with the Stoney Point tool.
These longer cases were relubed and were sized again. I eventually understood how to control this by A B and C above and each case came off of the press with exactly the same shoulder position and the same feel in the rifle chamber.

Let me know if you have any questions. You can also make the measurements using a Wilson gauge and a dial indicator. But the Wilson gauge will only work for a single caliber where the Stoney Point is more flexible and can measure a wider variety of cases.
 

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Discussion Starter #4
Thanks Ireload2,

What exactly are you talking about with the word, "dwell"? Are you suggesting to keep the ram in the upper most position for a few seconds before lowering it again?

I like your suggestion about rotating the brass a few times and resizing it again. Makes sense that it would tend to uniform the brass. Question, do you have to be concerned about over-working the brass when you do this?

Just to be clear, my measurements that I listed are from brass that has been fired and not re-sized. The brass has been fired once or twice at the most.

From reading I've been doing, it sounds like I should fire this brass several times while neck sizing only to get a true representation of my chamber.

Does anyone know if the RCBS mics are any less or more accurate than the Hornady or Sinclair bump gauges? Are the RCBS mics made from metal or plastic? Metal I hope.
 

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RCBS Pricision Mics are steel. They are supposed to be gauged and used for measurement, not just as a comparator. The "Zero" on the Mics is supposed to represent the SAAMI cartridge minimum dimension. This information is contained in the Mic's instructions. I use them as a comparator, along with the old Stoney Point case length gauges. The two different styles of gauges have two different diameters at the datum rings, but both work very well independently of each other. I use both, consecutively, to compare shoulder angles of cartridges after they are fired, then again after they are sized.

Allen
 

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Ireload2, I reload as you do with one exception, #C above. I had not thought about that procedure, but am sure going to give it a try.

Allen
 

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RE: calipers Resolution and Accuracy comments.
A "Long Scale Vernier Caliper" can be read to .0001" with Practice and Experience IF teh vernier is designed to allow it.
A "short scale Vernier caliper" can only be read to .001" even with long Practice and Experience.
A Dial Caliper that has .001 Graduations on the dial, IF checked against Gauge Blocks, may be interpolated to about .0002" or .0003".
A Dial Caliper by itself is only good to measure to +/-.001"
A Digital Readout Caliper uses a magnetic or optical scale tha tis usually only good to +/-.0005" so if you have a Readout showing a Forth digit to the Right of the Decimal watch it as you move the Slider, I bet you will see it move in .0005" increments.

Micrometer style Measuring Tools usually are moved by a Screw thread, fo r"inch" types usully 40 threads per inch which yields .025" per Revolution and can be purchase d with resolutions to .0001" at reasonable prices and .00001" for High Prices (which also need a Controlled environment to be used to their capabilities).

I am not aware of any hand portable and usable measurement method or tool that can consistently
and Repeatably measure closer than +/-.0001" in a 'Shop Environment with expert use.

Best Regards,
Chev. William
 

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I have two of the Precision Mic tools for cartridges that are supposed to use the same headspace gage (.30-06 and .270). Unfortunately, neither of them agree with the headspace gage I bought, and they don't agree with each other, as well.

So they are a useful tool as a comparator, but I wouldn't trust them to check headspace.
 

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Same here, my Precision Mic reads a SAAMI "go" gauge at -.003".

I usually just use it to measure the shoulder and then set it back .002" from there, so basically I use it as a comparator.
 

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All kinds of things happen to brass after being fired that affects the dimensions. Even new brass should be sized an measured before the first load. I measure my brass only after sizing and trimming. I find that for most purposes, consistency out to three places is good enough. Expecting consistency out to four places is just putting an extra burden on yourself for little gain in accuracy. Just my dos centavos on this subject. YMMV
 

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I have two of the Precision Mic tools for cartridges that are supposed to use the same headspace gage (.30-06 and .270). Unfortunately, neither of them agree with the headspace gage I bought, and they don't agree with each other, as well.

So they are a useful tool as a comparator, but I wouldn't trust them to check headspace.
I agree with you, but the point of the tool is to measure FIRED cases and then give you a datum point for your resizing measurement. Works extremely well and precisely as designed. I find them far easier to use than the Stoney Point type that I have, no where near as precise as the Precision Mic.

Cheers.
:D
 

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Life can be much simpler if you use a wood match and smoke your neck and shoulder, the set the die about a pennys depth off the shell holder, and run it up the sizing die then look at the mark, then try it in your rifle. keep doing this until you bolt closes slightly snug, and your case is custom fitted to that particular gun, then I usually take another turn on the die just to be sure it feeds, as first and foremost I'm a hunter and function is my first priority...Keep it simple.. BTW is you change bullets then do this step all over is a pretty good idea..
 
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