Once-fired cartridge headspace variation?

[Don Fischer]

WOW! I'm getting confused here! As I understood it the guy has three different overall length's. If that the case then what he need's is a trimmer, not moving the shoulder any where. Once the case's are all trimmed below max length, then they have to fit the chamber of the rifle they will be used in or, FL sized every time. FL every time is a good way to go but, you have to understand each chamber is a bit different and you might in fact be sizing more than is needed. To get the case to fit your chamber require's setting it up to do just that. Pretty simple but take's several loading's to get it done. Screw the FL die down to the shell holder then back it out till you can see about an 1'8th inch between them. Re-size the case right there. All that will be sized is the neck of the case and it will work in your rifle. Keep doing that till the sized case will no longer chamber in the rifle you've been shooting it in. At that point start screwing the die in maybe 1/2 turn at a time. Each time take that case out and put it in the chamber of your rifle and try to close the bolt on it, don't force it! Keep doing that, a bit at a time till the bolt chose's easily on the case in the chamber. Lock the die in right there and dedicate that die to that rifle. Be sure it lock's right there. Now what you've done is what a lot of guy's call bumping the shoulder. In fact you have FL sized the case to fit the chamber you are shooting it in. You cannot Bump the shoulder of a case without getting the sides also! Can't be done. What you will have is a case that fit's the chamber of that rifle, might not go into another and maybe it will but the only one it fits right will be that one rifle.

On this overall length thing. measuring with a comparator will not give you overall length, measuring with a with caliper's will. It's a measurement from the back of the case to the end of the neck. If it get's to long, you risk jamming the case into the lands and that doesn't let the bullet go until pressure is well beyond what you want. The OLL is printed for every cartridge in the Hornady manual and I'd assume in the other's too, Hornady is my most used manual. It'll tell you a max length and a trim to length. As long as your under max length your good. But, don't bother measuring the case until after you have resized it. When you re-size it, the expanding button going through the neck of the case will stretch the case more than firing.

 

[Metal god]

Don , I hope I understood what he was saying . Maybe the OP can come back to clarify ?

When trying to set up my die to resize just .001 below the fired cartridge size, measured using Hornady caliper attachment,

I took this to mean the OP is trying to bump his shoulders back .001 and is using the Hornady headspace gauge .
https://www.midwayusa.com/product/4...headspace-gauge-5-bushing-set-with-comparator

This is why I went the direction I did in my answers . If he was talking only about case length then you are correct .

 

[F. Guffey]

WOW! I'm getting confused here! As I understood it the guy has three different overall length's. If that the case then what he need's is a trimmer, not moving the shoulder any where.

Don't blame me: I have said for years reloaders are infatuated with head space. anything head space, it seems if they use the term head space it elevates their status. Not me, I do not know how a reloader could misunderstand 'the length of the case from the shoulder/datumn to the case head'. And then there are those that insist on getting it wrong and should know better; they tell me everyone understands what he meant. Again, the case does not have head space: it is in the book.

I listed the datum diameter as .375".

F. Guffey

 

[F. Guffey]

Old Yesterday, 10:10 PM #22

Don , I hope I understood what he was saying . Maybe the OP can come back to clarify ?


Quote:
Originally Posted by YM13
When trying to set up my die to resize just .001 below the fired cartridge size, measured using Hornady caliper attachment,

I took this to mean the OP is trying to bump his shoulders back .001 and is using the Hornady headspace gauge .

I suggested he approach reloading a little slower, I believe he should learn to walk before hitting it in a dead run. I thought the .001" was more than a little to ambitious. And then there is bumping; "I bump". How does a reloader bump the shoulder back? Hornady head space gage: There is another opportunity to use the phrase 'head space'. Head space gages do not have radius' on the datum.

I did suggest he purchases a Wilson case gage, again the Wilson Case gage is a datum based gage. the Wilson case gage has a radius on the datum, Hornady could take a few lessons from Wilson or they could take a Wilson case gage apart to determine how it is done.

Or you guys can keep on assuming you know what the OPs are saying/asking.

F. Guffey

 

[F. Guffey]

"If I set up my 308 die as suggested above . My cases come out .009 shorter then my fire formed cases .After 3 loading I got these case head separations"

I used to have a .308 like that. Setting the barrel back a thread and a new chamber FIXED IT.

Mobuck, I can not find the quote, I do not have a 308W like that but (again) I have a 30/06 like that. It is a very common rifle, the chamber is .002" longer than a field reject length gage: MEANING the chamber is .016" longer from the shoulder to the bolt face than a minimum length/full length sized case when measured from the shoulder of the case to the case head.

And then there is the assumption reloader make when they are confused about head space. They assume I am going to suffer case head separation. They assume the shoulder on my case is going to move forward .016". And I keep saying there has got to be something the reloader does not understand about the sequences of events that happens between pulling the trigger and the bullet leaving the barrel.

Shorter/longer: Again, The Wilson case gage is a datum based tool; if the reloader understood the Wilson case gage we would not be having this conversation, and for years reloaders referred to the Wilson case gage as a 'drop-in gage. You know, drop the case into the gage and use your thumb/finger nail.

F. Guffey

 

[cw308]

I get my 308 brass from a shooting buddy the doesn't reload . I F/L size his brass as listed in the instructions . the fired brass will fire form to your chamber & spring back .001, it not only stretches it expands too , would give you a measurement that the fired brass is shorter the when you started with the full sized setup . Then I F/L size to that fired form measurement . I ordered a Go Gage to check my chamber length , with a 308 the chamber is 1.630 by shimming I found my chamber is 1.632

I don't load hot , my brass needs very little sizing . you can strip your bolt feed in a oversized case, slowly size an check until the bolt closes with very little resistance , then check that measurement for your chamber length. Just remember not all cases expand the same , they will be close but not all exact.

 

[Unclenick]

YM13,

Brass has some degree of elasticity so it expands to fill the chamber under pressure and then the chamber and brass go on to expand together as the pressure increases further, and then they spring back some. Within safe pressures, the steel springs back all the way to its original size. Steel has a much wider elastic range than brass does (this is why you can make a better spring from it). Brass has generally had its yield point (where flow goes from elastic to plastic) exceeded at some point during firing of a high power rifle cartridge, so it gets larger in the chamber, but still springs back a little. How close it gets to the chamber size then depends on if the pressure was high enough to also stretch the steel with it enough that the brass got so big that its smaller elastic range doesn't spring it back below the chamber size. Beyond that pressure you get sticky bolt lift because the steel chamber stretched enough to allow the brass to get enough beyond its zero pressure chamber size that when the chamber returns to size it actually clamps down on the now-oversized brass.

So, the bottom line here is that the fire-formed brass will only match the chamber size exactly after just one firing if a particular pressure profile was exactly achieved. Commercial loads are not normally loaded that high and they are not all loaded to the exact same pressure anyway, as they have different lots of different powders with different burn rates to his a test barrel velocity range with. As a result, they are usually somewhat below SAAMI maximum. So, you get quite a bit of variation in how close to chamber size their brass is after just one firing of the commercial load. It is not normal for them to fail to re-chamber afterward unless the pressure was unusually high, which does happen very occasionally. Indeed, as mentioned, neck sizing-only (what the Classic Lee Loader does, for example) would not work at all if they did get that tight on one firing. In general, that only happens with loads exceeding normal SAAMI commercial load pressure limits.

People who neck-size only often find that after a number of reloads the case finally stretches enough that it starts to get a a little snug when re-chambering. At that point it has finally grown to full chamber size and perhaps a little over, so it has to be full-length resized once to be usable again. (By then the neck also usually needs its neck and shoulder annealed, too.) So, you can do some shooting with neck sizing only. Zero your comparator against the caliper and measure and record the change in size after each firing and when it gets to dragging on chambering, figure the previous measurement reflected the true headspace pretty closely or else it is between the current measurement and the last. Use that measurement and set up the die for shoulder setback from that value.

As pointed out earlier, the comparator does not give you an absolute measurement. It comes up short because of the slight radius in the datum diameter hole in the case comparator insert. If you want an absolute measurement you have to measure a headspace gauge to find the minus error, then go back and add that amount to all your other measurements made with the gauge. But as Mr. Guffey will point out, that is irrelevant as you really only care about not over-resizing the brass after you have your chamber dimension worked out.

Where is all this coming from? If you look at the SAAMI standard, you will find there is a minimum length chamber headspace for standard chambers. For the .270 Winchester that minimum is 2.0456" from breech face (the bolt face in a bolt rifle) to the datum diameter on the shoulder. If you measure commercial ammunition or new cases, it will be formed shorter than that so as to be sure to feed from a magazine into a minimum headspace chamber. In modern cartridges, like the .308 Winchester, the commercial brass length from the bottom "face" of the head to that same datum diameter is typically -0.002" to -0.003" shorter than the minimum chamber. This is where the idea of setting back that much to guarantee function comes from. Setting back only 0.001" is to allow the case to self-center in the chamber, but otherwise have no extra resizing.

There is an added complication with the older rimless cartridges that are decedents of the .30-03, like your .270 Win or the .30-06. They were developed when headspace was taken as the length from the breech face to the intercept of the chamber side wall and shoulder. They wanted contact made there by the case shoulder, so the case shoulder angle is made a little steeper than the chamber shoulder angle. In the .270 Win it is a ¼° difference in the half angle SAAMI uses, or ½° difference in the full shoulder angle. This means that when a sharp shoulder case just touches and centers in the chamber shoulder at that outside shoulder location, there will already be a 0.0017" gap between the case shoulder and the chamber shoulder at the datum diameter. But in reality that is modified by the shoulder/body junction radius, bringing it down to about 0.0015". The bottom line is that to guarantee magazine feed, you want to set a .270 or a .30-06 shoulder back about 0.0035" shorter than chamber headspace, and to just set it back enough to self-center, you want about 0.0025" of setback from chamber headspace. But first you have to determine the chamber headspace. That can be done by multiple neck sized-only firings of the same case, as described above. There are other methods, but I'll leave that for a different day.

 

[F. Guffey]

Where is all this coming from? If you look at the SAAMI standard, you will find there is a minimum length chamber headspace for standard chambers. For the .270 Winchester that minimum is 2.0456" from breech face (the bolt face in a bolt rifle) to the datum diameter on the shoulder. If you measure commercial ammunition or new cases, it will be formed shorter than that so as to be sure to feed from a magazine into a minimum headspace chamber. In modern cartridges, like the .308 Winchester, the commercial brass length from the bottom "face" of the head to that same datum diameter is typically -0.002" to -0.003" shorter than the minimum chamber. This is where the idea of setting back that much to guarantee function comes from. Setting back only 0.001" is to allow the case to self-center in the chamber, but otherwise have no extra resizing.

If you measure commercial ammunition or new cases, it will be formed shorter than that so as to be sure to feed from a magazine into a minimum headspace chamber

Again, I do not recommend putting a new reloader into a dead run, there is a chance he can keep up, if he can the datum for the 308W is .400", that falls into the category of nice to know if the reloader understands the difference between a case gage and a case head space gage. Again, the case does not have head space but many reloaders purchased a comparator/height gage called the digital head space gage. Measure before and again after.

The length of the case is one thing and the OAL is another and then there is COL if O is used for overall.

If you measure commercial ammunition or new cases, it will be formed shorter than that so as to be sure to feed from a magazine into a minimum headspace chamber

In the perfect world when working with 30/06 cases a minimum length/full length sized case is .005" shorter from the shoulder to the case head than the go-gage length chamber. A reloader with a few shop skills should have no problem measuring the distance from the shoulder of the sizing die to the deck of the shell holder. In the perfect world and a once fired case there should be .125" case head protrusion from the die after sizing. The problem for most reloaders is figuring out how to get the die out of the press without lowering the ram. because we all should know when the ram is lowered the case is removed from the die.

To save time I use feeler gages when I want to know if the case has more resistance to sizing than the lube, die and press can overcome.

F. Guffey

 

[YM13]

Hey guys, thank you so much for the informative replies. Sorry I stopped receiving automatic replies and took forever to post the numbers.

I am using the Hornady Headspace Comparator. I understand what headspace is. I'm sorry if confused some of you regarding what I meant; however, this is the name of the tool and therefore I used the term a bit loosely perhaps.

Regarding the numbers...they are a bit closer than what I remember or was left with as an impression (below).

Winchester Brass (20 rounds/brass -once fired and head sized on Lee Hand Loader):
-All measure right around 2.0430 with very minor variance, around .0005-.001 on one or two.

Federal Premium (Unfired Brass):
-Varies quite a bit but I separated about half of the cartridges measure right around 2.0400-2.0415.
-The other half measure somewhere in the 2.03's. I put those to the side for now.

Rem. CoreLokt
(Once Fired - 17 rounds/brass)
-~2.0410

(Unfired, 3 rounds)
- 2.0410, 2.0395, 2.0395

These observations mainly let to my Q: (1) If you look at the unfired to fired measurements, they do not vary much at all. I would assume this is not a bad thing but probably good, indicating a good, close fit of the brass (i.e. not much expansion); however, the previously fired Winchester Brass, although they were neck sized on the Lee Hand Loader, show a greater measurement.

My Q is more aimed at understanding and setting up my reloading process correctly from the start, thus why I wanted to engage in some dialogue with you knowledgeable folks.

Thanks!

 

[cw308]

The RCBS Precision Mic I found to be the easiest an precise tool for case & ogive measurements.

 

[Unclenick]

however, the previously fired Winchester Brass, although they were neck sized on the Lee Hand Loader, show a greater measurement.

Exactly so. The longer neck-sized-only cases are coming closer to your true chamber size, less the error from the comparator insert's hole radius. Actual values, assuming the chamber is within SAAMI specifications, would be 2.0487"-2.0587". Most guns will average about 2.0489" from the factory, so your particular copy of the Hornady insert is probably reading -0.006" or -0.007" below absolute. Mine all vary from -0.004" to -0.009", so yours are in the same ballpark.

If you neck size those cases again and fire them again several more times, you'll continue to get a little closer to full chamber size each time until they either start to get hard to chamber or just stop growing. The former happens with higher pressure loads and the latter with very mild loads. The Lee dippers, if you are using them with a Classic Lee Loader or if you are neck sizing using the Lee Hand Tool (actually a hand press for standard dies; I'm not sure which you mean), usually produce pretty mild loads because they have to be sized to allow for some lot-to-lot variation in the bulk density of each powder type.

I own three of the RCBS precision Mic's (.223, .308 Win, and .30-06) I picked up in the past. Their accuracy, based on checking their zero reading against a good quality headspace GO gauge, varies, with the worst one being about +0.0025" from absolute by the gauge. So you still need a gauge to calibrate to for absolute measurements, same as the Hornady tool does. It is easier to read between thousandths on the RCBS tool once you know the calibration allowance and if that level of precision interests you. The downside is it takes longer to screw the graduated thimbles in and out than it does to close the jaws on a caliper. The modern electronic calipers also let you zero on a GO gauge (or you can use a NO-GO or a Field Reject gauge; as long as you know the value they are ground to), then just read plus or minus on the caliper and then add that to the gauge value to know the absolute number, if that matters to you. For reloading, though, you just need the comparison value.

Below are photos I took showing how a 0.375" ID bushing can serve as a poor man's caliper comparator. A spacer with 3/8" hole will work, too. Many folks like to use and inverted pistol cartridge case, but I find some of those are oval, due to uneven wall thickness and too much springiness, so I haven't been satisfied that I get consistent result with them, but you can try.

Zeroed on a headspace GO gauge.

This case is 0.003" over chamber minimum. Allowing for spring-back, The actual chamber is probably more like 0.004"–0.005" over minimum since this case has only been fired once.

Headspace Go gauges.

If you go to buy a GO gauge to calibrate your tool against, these days I like the tools Dave Manson produces best. All the gauges I have from him have measured to be within half a thousandth of the labeled value. I can't make a tighter determination than that on my equipment, so they could be within a tenth of a thousandth and I wouldn't know, but half a thousandth is as tight as a SAAMI pressure and velocity test barrel chamber that pressure and velocity data are taken from, so I can't do any better in trying to compare to one.

 

[F. Guffey]

There us a limit and or a wall reloaders hit so going forward is not going to happen. I have always suggested the reloader learn to measure the length of the chamber from the shoulder to the bolt face; the wall: The first tool a reloaders reaches for is the go-gage, not me, I reach for the long gage. I have offered to modify go-gages to a 'go-to infinity gage', problem, I have to convince them it can be done. I have suggested the no-go gage is the better/more useful tool than the go-gage and the filed reject length gage is my preferred tool of all three and about all I can get in return are blank responses.

And then I wonder; if a reloader can manage to operate all of these tools why can't they measure the length of the chamber from the shoulder of the chamber to the bolt face without a head space gage?

I have made shop calls. the builder of the rifle had 20 30/06 head space gages and could not determine the length of the chamber from the shoulder of the chamber to the bolt face. He handed me the box of gages in an effort to help. I explained to him I knew all the go-gages would allow the bolt to close, I explained to him I knew there was a big chance the bolt would not close on the nogo-gage. I gave the builder three choices/methods for measuring the length of the chamber in thousandths without a go-gage. It seemed that was more effort than he wanted to invest in the task so I measured the length of the chamber for him. He had .0075" clearance between the shoulder of the chamber and shoulder of the case if the case was minimum length/full length sized. I offered to off set the length of the chamber with the length of the case from the shoulder to the case head.

I offered to check close to 135 bolts for their ability to off set the length of the chamber by .0025"; problem, the bolt had to be period correct.

F. Guffey

 

[YM13]

Unclenick, neat alternatives to measuring the cartridges and thanks for the info regarding the expansion of the cases upon each subsequent firing.

Now, the question is, should I use the Lee Collet die to neck size when full resizing is inevitable at some point? Or should I just go ahead and do a full resize with minimal working of the brass (i.e. .001” less than fired”)?

My worry is that I will have to adjust the loads depending on resizing process I use as the full length die creates noticeably greater neck tension than the neck resizing die. This will most likely affect pressure and perhaps point of impact?

I realize this is the subject of some contention amongst reloaders so I may have to do some shooting and experimenting myself to see just how the rounds react in terms of accuracy, etc.

Thanks guys!

 

[Metal god]

I wish I could help you on the neck sizing only . I did some limited test on that and did not notice a difference then FL sizing . I have the Redding neck die as well as the Lee collet dies so I'll likely try it again some day .

As for FL sizing , I use the Redding competition shell holders to adjust my case headspace to be consistently .002 shorter then my fire formed cases . If setting up your die as Mobuck explained earlier and your cases are sized down to much . You can use the Redding competition shell holders to size your cases longer in .002 increments while still have hard contact between the die and shell holder ( with cam over if applicable ).

This is helpful because most if not all presses have some flex or deflection when sizing a case . If you are not making hard contact between the die and shell holder . That flex/deflection can cause your cases to be sized inconsistently . Especially when you are only trying to bump the shoulders back .001 or so .

Here is an example of press flex/deflection . The die in both photos is set up the same to just barely make contact with the shell holder with the ram is fully up .

This is with no case in the die being sized , notice no gap between the die and shell holder

Same press and die set up but this time I am sizing a case , notice the gap that is now present between the die and shell holder .

That flex/deflection was .007+ . With that much variance when only trying to size a case by .001 will cause some shoulders to be set back .003 shorter then intended while others may not be set back at all .

The Redding competition shell holder set is specifically designed to allow the die and shell holder to make hard contact while still being able to size your cases longer ( head to datum point ) in .002 increments depending on the shell holder you use .

https://www.midwayusa.com/s?userSearchQuery=Redding+competition+shell+holders&userItemsPerPage=48

The Redding Compeition Shellholder Kit #10 consists of five shellholders in varying heights with increments of .002". Allows you to increase or decrease the case to chamber headspace without adjusting the dies.

Which has another benefit which is when loading for multiple rifle of the same caliber . I have not adjusted the lock ring on any of the dies where I use the comp shell holders since I started using them . I just use the appropriate shell holder for the rifles chamber never having to adjust my dies .

I need to copy and paste this post to my note pad or something . I've written this same thing maybe 30 or 40 times over the years in multiple forums and I'm kind of tired of writing it out every time this comes up haha .

Hope that helps .

 

[YM13]

That is great to know! Did not realize that much deflection could occur. You probably saved me a good bit of scratching my head there wondering what is going on.

 

[F. Guffey]

That is great to know! Did not realize that much deflection could occur. You probably saved me a good bit of scratching my head there wondering what is going on.

When the case has more resistance to sizing than the press can overcome a gap is created between the bottom of the die and the top of the shell holder. Again, when that happens the reloader can lower the die an additional fraction of a turn like 1/4, 1/2 or 3/4, at one time it was fashionable to grind the bottom of the die and or the top of the shell holder,

Instead of grinding mindlessly if it was necessary to increase the presses ability to overcome the cases ability to resist sizing I used a feeler gage between the deck of the shell holder and case head. If I needed something like a small base die? Same thing, I added the shim between the deck of the shell holder and case head, POINT? I knew my press was getting whipped by the case of I needed a small base die.

F. Guffey

 

[F. Guffey]

This is helpful because most if not all presses have some flex or deflection when sizing a case . If you are not making hard contact between the die and shell holder . That flex/deflection can cause your cases to be sized inconsistently . Especially when you are only trying to bump the shoulders back .001 or so .

Unbelievable, my instructions from RCBS for presses claim the cam over press is a bump press, another set of instructions for another press claim the non cam over press is not a bump press. And then it comes down to adjusting the die, the instructions claim the two presses require a different technique when adjusting. I can reduce the length of a case from the shoulder to the case head, .001"? When I reduce the length of a case .001" I am using a hint of effort I have old presses with heavy handles, when using one of those presses I do not turn my back on them because I a good case could be made for there intent; they are out to get me. An old experienced reloader should be able to look at the press and its design to know caution is advised.

I made a shop call, for my friend it was not going well, he locked up an A-2 press. I used a feeler gage to check the gap between the top of the shell holder and bottom of the die, the gap was .037" I did not bring a strain gage, I did not bring a deflection gage. He could not understand why he could not move the handle and he could not determine why the ram would not move down. He could not understand why the ram had to raise/travel up before it would travel down. Anyhow, I remove the die with a pipe wrench, it was his die not my die.

F. Guffey