Resizing question

[mofosheee]

Suppose I take a case of fire formed brass from my AR. I bump the shoulder back 0.002" using a full length re-sizing die. Measuring that case in my comparator/ calipers, that case becomes my referrence and that
all future cases ran through that undisturbed re-sizing die will be close to the reference. Correct?
Moving on, I grab a handfull of range brass measure it to find most of it is oversize by 0.002" - 0.005" (ish). I run them through the sizing die and they all zero out. No problemo.
Some of the cases measure -0.002 or -0.003" (negitive) undersize to my reference brass before being run through the resizing die. When these cases were run through the die I'm thinking that they would not
be brought back to 0.000" affecting my headspace ........... but these cases zero'ed out.
The question is, am I correct to assume that the reforming (resizing) process also forces brass to conform/flow within the die whether the brass is smaller or larger (within limitations)
hope this makes sense.
Thanks again!

 

[jmorris]

all future cases ran through that undisturbed re-sizing die will be close to the reference. Correct?

What does "close" mean to you in thousandths of a inch?

Like finger prints, there are no identical two cases, so I don't expect them to all be completely identical, even if all from the same lot, fired the same number of times, with the same load, from the same firearm. I would expect them to be closer to one another than a handfull of mixed brass fired from any number of other firearms though.

 

[AJC1]

The purpose of sizing is to ensure fit, and uniformity. If your sized brass is changing dimension after you size it again, something has changed. The position of your comparator on your caliper, the expander ball pulling on the neck. Simple things like temprature makes a difference in very small measurements. Establish a tolerance that is manageable and reasonable. Your brass doesn't need to be perfect, it's not like your launching the hubble into outer space with a main mirror ground out of spec.

 

[mofosheee]

The purpose of sizing is to ensure fit, and uniformity. If your sized brass is changing dimension after you size it again, something has changed. The position of your comparator on your caliper, the expander ball pulling on the neck. Simple things like temprature makes a difference in very small measurements. Establish a tolerance that is manageable and reasonable. Your brass doesn't need to be perfect, it's not like your launching the hubble into outer space with a main mirror ground out of spec.

I'm new and it's an OCD thing
Thanks

 

[jmorris]

Simple things like temprature makes a difference in very small measurements.

How someone holds and uses calipers can lead to variation in readings.

Why I always suggest folks use standards when getting a feel for them. Once you are getting the correct measurements, repeatedly, you are using them correctly.



Even then, the best caliper still won't be as accurate as an inexpensive micrometer...

 

[lightman]

This is one reason I use the bolt close method more than anything else. Different brands of brass can be slightly different alloys and throw your numbers off. When you start measuring to 3 decimal places you can get to the point of scratching your head and chasing your tail! I guess thats a long winded way of saying don't get too caught up in the numbers!

 

[243winxb]

The question is, am I correct to assume that the reforming (resizing) process also forces brass to conform/flow within the die whether the brass is smaller or larger (within limitations)

When a 223 case body is sized smaller, the head to datum gets longer, as does the trim length. Edit/Add . As Walkalong said below- Until it hits the shoulder on the die and starts getting moved back.

Brass may need 3 firings, neck sized, to fully expand to the chamber..

Two things can set the shoulder back, shorter head to datum, , at times.
1. Slaming a AR15 bolt on a datum that is to long.
2. The firing pin strike set back of .006" (Savage Axis bolt gun.)

 

[JFrank]

When these cases were run through the die I'm thinking that they would not
be brought back to 0.000" affecting my headspace ........... but these cases zero'ed out.

When a 223 case body is sized smaller, the head to datum gets longer, as does the trim length.

This ^^ .

 

[N555]

It depends on how much spring back the brass has.

 

[Walkalong]

When a 223 case body is sized smaller, the head to datum gets longer

Until it hits the shoulder on the die and starts getting moved back.................

 

[JFrank]

Until it hits the shoulder on the die and starts getting moved back.................

This ^^ been that way since the beginning.

 

[Varminterror]

Some of the cases measure -0.002 or -0.003" (negitive) undersize to my reference brass before being run through the resizing die. When these cases were run through the die I'm thinking that they would not
be brought back to 0.000" affecting my headspace ........... but these cases zero'ed out.
The question is, am I correct to assume that the reforming (resizing) process also forces brass to conform/flow within the die whether the brass is smaller or larger (within limitations)
hope this makes sense.

The rifle which fired that brass had a fat chamber. You squished the fat case back to a skinny case - like squeezing a cylinder of clay, it gets longer.