trim&resize vs. resize&trim

[liber]

My point ? S*#t happens , What happens when a case that never got trimmed gets in that lot you feel no need to trim ? better to be safe then sorry .

Yeah, I think I've just gotten a bit lazy as my numbers are so far off, but since I never go more than twice without trimming again, I've not worried about it.

Not a knock , just a friendly conversation .

No knock taken. I just wanted to see if the drama queens were on their toes!

This forum of all forums is the place people are watching for you load to be off a tenth of a grain, so no worries. In the end we can never be too safe and it is best to check each time. I've seen the Redding Instant Indicator that goes on your press and tells you about the case size, not sure if that would be a good solution or not.

As I mentioned I was thinking about trimming a bit longer, maybe .210" for 308, but don't think it will make too much difference for my loads as they're going in a magazine.

[ar15barrels]

Size, then trim. The other order makes no sense as the cartridge should not elongate upon firing only.

It's normal for a case to get SHORTER after firing and then LONGER after being sized again.

[kdsd731]

Chamfer and debur the cases.
Run then through the sizing die.
Measure them.
Trim if necessary.
Chamfer and debur the trimmed cases.
Clean and load.

[fguffey]

It's normal for a case to get SHORTER after firing and then LONGER after being sized again.

I do not know about after firing, I have cases that shorten during firing.

I'm using Giraud Tri-Way heads in my mill, they cost $90 for each caliber and I have one for 308 and one for 223.

No, I'm not checking them as I trim to .205" and the max allowable is .215". When I size, I only bump it about .001-.002, so there is no way the case can grow enough to exceed the max allowable, IMO.

Trimmers? Liber is using a trimmer that trims the length of the neck with a tool that is set up on the shoulder of the case. Other trimmers are set up to trim off of the case head. Problem for reloaders: The length of the case from the shoulder to the case head. The Wilson case gage measures the case from the datum/shoulder to the end of the case neck and from the datum/shoulder to the case head.

Complicated for most I know. I have a chamber that is .011" longer than a go-gage length chamber. When trimming I add .014" to the length of the case from the shoulder to the case head. A reloader that does not measure the length of the case from the shoulder of the case to the case head and trims the length of the neck with a trimmer that sits up on the shoulder will have cases with varying lengths.

F. Guffey

[ar15barrels]

I do not know about after firing, I have cases that shorten during firing.

A dimension can not be known if it is not measured.
I would be interested to see the setup you use to measure the case length DURING firing.
Most people can only measure a case after it has been fired as the gun is in the way of taking the measurement.
Therefore, we say that the case is shorter after firing because that's when we measured it.
Before we measured it, it was an unknown.

[fguffey]

I do not know about after firing,

What ever happens it happens when fired, after firing I determine the effect the chamber had on the case when fired. I measure after firing. I measure before firing and I measure after sizing.

Once I determine the length of the chamber from the shoulder of the chamber to the bolt face I can cut back on all that measuring. It is not necessary to start over everyday.

F. Guffey

I have cases that shorten .040" from the end of the neck to the case head from start to finish. Meaning I start with a case that has a case length of 2.494" and finish with a case that has a case length of 2.454".

F. Guffey

[liber]

A dimension can not be known if it is not measured.
I would be interested to see the setup you use to measure the case length DURING firing.

For once I did understand what Frank meant. At least if I understand his response to you, the change happens during firing, not after.

Another way to ask the same question would be. How does your case change after it is fired?

One thing I realized, speaking for myself, is that I do run them through my sizer twice. When I trim I process them once to size the neck prior to running them through the Tri-Way, then I just run them through the Dillon again after. I have measured them after running them through a second time but they don't seem to change in size, so I normally don't measure them at that point. I do check them when trimming them. The Tri-Way is not exact, but they are pretty close, like between .001-.002".

If you don't size before trimming you can't be certain the neck is concentric and the Tri-Way would be difficult to use if not.

[liber]

I do not know about after firing, I have cases that shorten during firing.

Randall also eluded to this, at least I believe both of you are talking about the same thing, although splitting each others words apart.

My question is how does that happen?

When the round fires, the case expands, and for most cases I have to imagine the headspace is closed as the head fills the chamber. Since the neck/shoulder is in the chamber, it is probably expanded slightly, at least in diameter.

Does the process of heating and cooling cause the necks to shrink? Otherwise it would seem that everything would cause the case to lengthen, either the body or the shoulder.

Since both of you say it shortens, why is that?

EDIT: I think I may have figured out why a case would shorten. In almost all chambers the neck will expand when fired, so maybe it is because the neck area is so small that it shortens, rather than making the neck thinner. Is that how the case shortens?

[ar15barrels]

Another way to ask the same question would be. How does your case change after it is fired?

Frank would tell you that it does not change after being fired.
He would tell you it changes DURING firing.
I would tell you that you can't measure the change until AFTER firing.
We would both be right.

[ar15barrels]

My question is how does that happen?

When the round fires, the case expands, and for most cases I have to imagine the headspace is closed as the head fills the chamber. Since the neck/shoulder is in the chamber, it is probably expanded slightly, at least in diameter.

Think of the brass as a piece of flexible tubing whose wall thickness doesn't change.
I'm not saying that brass does not change thickness, I'm just saying to THINK of it that way.
As the brass is pressed in ALL directions against the chamber by high pressure gasses and fills the chamber, the case shoulder and neck flow down into the chamber to aid in the case filling out the chamber.
When you size a case, it is squeezed back down to size and the extra brass is extruded (flows) back up into the case neck where you can measure the length of the case and see the change in length.

[liber]

Frank would tell you that it does not change after being fired.
He would tell you it changes DURING firing.
I would tell you that you can't measure the change until AFTER firing.
We would both be right.

I realize that and why I said you both were just splitting each others words.

Back to cases shortening during/after firing and/or lengthening during sizing.

Is this because the neck expands in the chamber when it is fired which causes the brass to shorten at the neck when that happens? I'm thinking that as the brass expands, it needs to get the brass from somewhere so it might take it from the length as that happens. In the case of the neck, it seems it can only use brass from the neck area.

And in contrast, when you size, it constricts the neck which causes the brass to lengthen as it has no other place to go?

[ar15barrels]

Back to cases shortening during/after firing and/or lengthening during sizing.

Is this because the neck expands in the chamber when it is fired which causes the brass to shorten at the neck when that happens? I'm thinking that as the brass expands, it needs to get the brass from somewhere so it might take it from the length as that happens. In the case of the neck, it seems it can only use brass from the neck area.

And in contrast, when you size, it constricts the neck which causes the brass to lengthen as it has no other place to go?

The whole BODY, SHOULDER and NECK expand during firing.
The extra brass necessary to fill out the chamber flows from the open end of the case (neck end) towards the case body.
During sizing, the BODY, SHOULDER and NECK get reduced in size.
The excess brass flows towards the open end (case neck).

I don't think you understand that the brass at the shoulder is actually flowing during this, not simply expanding and contracting in the same place.
Think about how playdoh behaves when you extrude the playdoh through the playdoh press.
That's how the cartridge case behaves at peak pressure.

[liber]

The whole BODY, SHOULDER and NECK expand during firing. The extra brass necessary to fill out the chamber flows from the open end of the case (neck end) towards the case body.

So this is where the case is shortened, when it flows from the open end of the case (neck end). You are correct below, I was previously envisioning a separation between the neck and shoulder thinking maybe it couldn't flow through the shoulder easily thinking the neck was shortened by itself from expanding in diameter.

During sizing, the BODY, SHOULDER and NECK get reduced in size. The excess brass flows towards the open end (case neck).

Ok, this makes more sense now also, the reverse of when it is fired

I don't think you understand that the brass at the shoulder is actually flowing during this, not simply expanding and contracting in the same place. Think about how playdoh behaves when you extrude the playdoh through the playdoh press. That's how the cartridge case behaves at peak pressure.

You're correct, I was envisioning that the case was only contracting and expanding at the neck, and didn't realize that it would pull that through the shoulder and body to the head.

Thank you for explaining it, I know some about working metal and how it moves, but have only been reloading for about 9 months, so still learning some of it. If others fault me for wanting to understand it, so be it. Some are quick to pound their chest and boost their own ego.

[LynnJr]

Size, then trim is an option. Then there are trim dies, another option. Trim dies come with instructions. Trim dies have been with experienced reloaders for decades.

F. Guffey

No Benchrest Shooter uses trim dies and they shoot the smallest groups fired each and every year.

[fguffey]

No Benchrest Shooter uses trim dies and they shoot the smallest groups fired each and every year.

When trimming there are options, the trim die is another option. Benchresters are not shooting the same rifle, there could be $2,000+ dollars difference. I did notice you just caught up with setting up on the shoulder for trimming. There is something outside of reloading called 'included'. When trimming a case while set up on the shoulder the length of the case from the shoulder to the case head is not included. Meaning? You are wrong about consistent case length, again the case has two lengths, one from the datum to the case head and the other from the datum to the end of the neck.

Going back to something as basic as the L.E. Wilson case gage. The Wilson case gage measures the case length from the datum to the end of the neck and from the datum to the case head. Most reloaders use the case gage as a 'drop-in' gage.

F. Guffey