Confused about Headspace

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Bullet said:
there are a lot of people that as SAAMI says- confuse headspace with head clearance .... The RCBS Precision Mic Cartridge Headspace Tool actually measures the case not headspace - the chamber.
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No confusion here. The chamber headspace dimension is the independent variable for the majority of reloaders. The cartridge headspace dimension is the dependent variable and for me is the only measurement I'm concerned with. When you measure cartridge headspace of a fired case, you are indirectly measuring chamber headspace, but better yet, you're obtaining a spring back measurement that's specific to the cases used (manufacturer) and the number of times the cases have been fired if you neck size only. I use Redding instant indicator comparators for all my rifle cartridges to measure the cartridge headspace (from case head to datum diameter) since this a dimension that affects ease of chambering and accuracy (and safety).

rcmodel said:
But if you are neck sizing only, none of the above 23 posts applies anyway, because they don't resize, or set back the shoulder which controls headspace.
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I neck size only but I also measure cartridge headspace and bump the shoulder back if necessary. So far, it hasn't been necessary on .300 Win Mag cases fired four times and .308 cases fired three times, both in Krieger barrels. I have had to bump the shoulder back on .300 WSM cases fired four times in a factory Remington barrel.

:)
 
Haskin, I missed you on another forum, if you blinked, you missed it, so much for the luxury of being able to disagree and one freedom I do not assume, the freedom of speech.

In the perfect world your 308 Winchester circle/hole/round datum is .400, from the circle/hole round datum (shoulder) back to the head of the case is 1.634, after that comes the argument, is that head space or the effect the case has on head space? I make gages to check head space and gages that determine the effect a case has on head space, again the perfect chamber is .005 longer from the bolt face of the chamber shoulder (2/5", .400 circle round hole) than the distance from the head of the case to shoulder on a perfect case.

When the bolt closes it gets dark, the lights go out---in the chamber, a term lost in reloading is 'transfer' my reloading dies are designed to full length size a case with clearance, with a perfect shell holder, sizer die and a good press I can size a perfect case for the perfect chamber, that is .005 shorter from the head of the case to the shoulder than the perfect chamber from the bolt face to the shoulder of the chamber. For chambers that are not perfect someone designed the press and die with threads that are adjustable, by making perfect adjustment for controlling shoulder sit back I can still size a case for a chamber that is not perfect that fits.

Again I have a M1917 Eddystone with .016 head space, that is .011 over the the length of the perfect chamber and presents .016 head space for the perfect store bought ammo, when the lights do not go out it is possible to shoot this rifle with .000 head space, I neck up 280 Remington cases to 30/06 then use a 30/06 forming die to move the shoulder back, the difference, I use a feeler gage to adjust the gap (.015) between the bottom of the die and top of the shell holder with the ram up, I believe that is the difference between doing it and talking about it.

Measuring fired cases, I have acquired once fired cases from many souses, cases that come from a/the range are mixed sets, with home made tools, I can sort cases and match them to chamber length, there are times I get lucky, I find cases that are fired in a chamber that is in dire need of adjustment, the long cases can be sized to shorter chambers when adjusted for head space----if head space is known, the amount of head space a chamber has is the first thing I determine, I make the gages first.

Haskin, thank you for posting on this forum:

F. Guffey
 
"But exactly how do I know if is “just right”?"

RC said it right. I told you how to achieve it.

Again, forget the technical headspace definitions of headspace, and clearance too, they offer no help to a newbie. And forget factory "die instructions" as well; factory set-up directions are NOT a law that can't be changed or you die. They can only hope to tell a beginner how to get started well enough for him to load some usable ammo. Seems very few people read and understand even the brief instructions included with the dies. (Maybe it's a result of "modern" education?)

YOU will have to learn how to achieve YOUR best cartridge fit from YOUR press and YOUR dies to match YOUR rifle. How to do that is what I tried to explain. And, yeah, using different cases for each effort is somewhat better, but not by a lot. ??
 
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Again, forget the technical headspace definitions of headspace, and clearance too, they offer no help to a newbie.
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Agreed

What is important here is what is dangerous, what is not, and how to make sure you do not have excessive clearance between the case and the breech, what ever one wants to call it.

Technically headspace is machined in to the chamber in reference to the ideal case dimension, and clearance is what we have between the case and the breech, but everyone calls it headspace. ;)

rcmodel described how to stay out of trouble with headspace/clearance/sloppy fit/ whatever.......quite a few posts back........ :)
 
Thanks again. This is how I understand the situation. For full length (non-carbide) resizing dies (which I will also use on occasion), I should only screw down the die just enough, such that after putting the loaded cartridge in the chamber, the bolt just closes with slight resistance on a sized case. If I do this (and make sure I trim any long cases to 2.005”), I should have no shoulder setback problem, and thus, I should not have to worry about headspace problems, correct?

And for Lee collet neck-sizing only dies (which are not carbide even though you do not use case lube on them), headspace issues don’t apply because these dies do not affect shoulder setback. Do I have it right?

One other related question. If I buy new unprimed brass and intend to use it with Lee collet dies, should I (or do I need to) full length resize the cases first, fire the cartridges in the rifle, and then use the collet dies thereafter? Or can I (should I) skip the full length resizing step? Thanks

Greg
 
Many folks size new brass, but many do not as well. There are good reasons for both, but it is not critical either way.
 
Greg, for what this is worth, the most accurate .308 Win. loads (winning matches, setting records and when testing for accuracy beating most benchrest records at longer ranges) have been from full length sized cases with their fired case shoulder set back a couple thousandths. Sierra Bullets sizes their bullet testing .308 Win. cases this way because they learned back in the early '50's that any bolt binding is a bad thing for accuracy. .308 Win. cases properly full length sized and fired in SAAMI spec chambers can get 50 to 80 reloads per case without annealing and only need to be trimmed back to length a few thousandths every dozen firings or so.

Nobody I know who wins matches and sets records lets any sized case cause any resistance when the bolt's closed. This only causes the bolt head to seat at different positions and accuracy goes down, unless you've got a zero tolerance bolt fit in the receiver. This is especially true with bolts whose face ain't squared with the chamber axis; fired cases have unsquare heads and they bind up on the high point on unsquared bolt faces.

It's my opinion (based on observations and measurements of fired and sized cases) that folks who get better accuracy with cases that bind when the bolt's closed are setting the fired case shoulder back way too far because their full length sizing die's set down too far. It takes a case headspace gage to measure cases and see exactly what's happening and enable the die to be set correctly.
 
I do agree with Bart about resistance on the bolt closing from to tight of a fit. The shoulder needs to be bumped back just a tad to chamber easily. This can best be done with the firing pin assembly out of the bolt when you set up your sizer. Adjust until the resistance just goes away. You can buy tools to measure these things if you wan't to really fine tune it, but the old fashioned way will work just fine.
 
I do agree with Bart about resistance on the bolt closing from to tight of a fit. The shoulder needs to be bumped back just a tad to chamber easily. You can buy tools to measure these things if you wan't to really fine tune it, but the old fashioned way will work just fine.
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Right you are Walkalong. Sinclair and many other retailers will happily sell you gauges to measure case headspace. Sadly, none of them sell any tools or gauges to measure head clearance.;)

http://www.sinclairintl.com/product/11239/Case-Gauges-Headspace-Tools

Don
 
"Bump back just a tad" Bump sounds like an accident, tad does not have a value, bump and tad are two words that are not in my vocabulary, one word I use quite often is FEELER GAGE, I have confidence in my shell holders, dies and presses. There is not a better tool made for checking head space on a Springfield 03, 03A3 etc. than the feeler gage or for indexing a barrel, the only problem? Hatcher did not think of it.

F. Guffey

_________________________________________________________________

The bolt closes, the light goes out and the chamber is dark and not understood
 
"Bump back just a tad" Bump sounds like an accident, tad does not have a value, bump and tad are two words that are not in my vocabulary, one word I use quite often is FEELER GAGE
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I know plenty of folks who know exactly what "bump" and "tad" mean. :D

There are so many tools and gauges and other goodies available these days, that we don't have to just "bump" it a "tad". We can measure things to our hearts content.

Many new reloaders don't have the excess cash to buy a lot of extras, so the old bump it a tad until it just fits with a "gnat hair" of clearence works just as well as those of us who carefully measure everything. (And I don't on many things)

Folks have been doing this with success for more years than I have been around. :)
 
Headspace is a chamber shoulder to bolt face dimension that has nothing to do with the case dimensions at all. Headspace for a rimless case is the distance from the bolt face to a datum point on the reamed shoulder. Look at a headspace gage. It measures the chamber shoulder datum to bolt face dimension only.
 
:D The more I read all this the more I get a kick out of all this fancy and technical explantion of a very simple thing. I bet I'm the only one on here that has a Winchester model 94 that headspaces on the case shoulder instead of the case rim...;)
 
I bet you're not! ;)

Anyway, how this got to the point it got too is beyond me.

From a reloading standpoint, you can and do change the artificial headspace, or whatever you want to call it, of the cartridge you are loading with the FL sizing die.

Whether or not that answers the OP's question I don't know.
But I thought we had it covered in the first few posts.

rc
 
Hey folks, my head is spinning! I really appreciate the response, but I’m still confused. I know I started this very interesting debate way back in Post No. 1, but you guys are too advanced for me. I appreciate now that this is a subject in which there is NOT 100% agreement when it comes to the finer details.

But since I am a relative newbie, I am not looking for the best possible accuracy and case longevity. One inch groups at 100 yards would be fine with me and having my cases go 20 firings using lower pressure sub-max loads would be fine with me too. I do not want to buy any specialized tools to measure head space if I really don’t absolutely need to. Therefore, will I be just fine if I simply do the follow:

1. Follow the instructions on the press and screw in the sizing die (full case) 1/3 of a turn (the instructions say between ¼ to ½).
2. Check to see if the bolt closes without resistance on a test cartridge (no primer or powder).
3. If I feel resistance, screw down the sizing die another 1/8 turn and try again with another test cartridge. Repeat, as necessary, until bolt closes without resistance. Save this setting.
Anything incorrect?

If you have the time, I have these related questions:

A. I am not sure I understand the “shoulder setback” issues too well. I think I understand it after reading some of your posts, but when I read others, I’m lost again. To avoid confusing me further, please, rather than you providing me your own explanation, can anyone simply tell me what part of my OWN explanation is INCORRECT: If you screw the sizing die (full case) in too little, it will result in the shoulder of the case being set too high and if you screw the die in too much, it will result in the shoulder being set too low. Shoulders set too high and too low are not good, however some shooters like to go slightly high (for .308 and other cartridges that head space on shoulder) in order to make the cartridge fit a tad more snuggly in the chamber. Therefore a slightly high shoulder is OK and sometimes preferable, but a slightly low shoulder is not. Finally, if I do the above and also not allow the length of the case to exceed 2.015” (.308 Win), I should not have to worry about measuring headspace. How was that?

B. Is it true that neck sizing dies do not affect shoulder setback because the only part of the case being sized is the neck? But, if you neck size a case that previously has a bad shoulder setback, it will still have a bad shoulder setback, right?

C. I understand that there are different opinions on whether to full size new brass (versus not) before neck sizing. Are the any good reasons for doing one versus the other?

Thanks again for all the time you guys are spending on this. Wow!!

Greg
 
The only thing I can add to my first post is:

If the case head to shoulder datum line is already too short, it will expand and stretch to fit the gun.
Repeated FL sizing and pushing the shoulder back too far will result in it stretching to fit the rifle every time you fire it.

Too much stretching each firing / sizing cycle will result in case failure from head separation.

Most dies sets & shell holders, if screwed down against the shell holder and then tightened an additional 1/8 - 1/4 turn to take out all press linkage slack & frame spring, will give you very close to SAAMI spec shoulder length.
But not always.

Maximum Case Length or excessive case length has nothing to do with headspace.
That is a separate issue, and if the case is too long OAL, the mouth will get into the rifling leade and not be able to expand enough to release the bullet freely.

rc
 
"Maximum Case Length or excessive case length has nothing to do with head space.
That is a separate issue, and if the case is too long OAL, the mouth will get into the rifling leade and not be able to expand enough to release the bullet freely"

The mouth of the case is a long way from the rifling, lands etc., all of my chambers have a throat between the end of the chamber neck and rifling.

And I do not agree the first responders response are the only responses that count, I do not have an inflated opinion of the value of my contribution, read through the first responses and look for 'adjust a little' and 'the firing pin drives the case forward'.

F. Guffey
 
1. Follow the instructions on the press and screw in the sizing die (full case) 1/3 of a turn (the instructions say between ¼ to ½).
2. Check to see if the bolt closes without resistance on a test cartridge (no primer or powder).
3. If I feel resistance, screw down the sizing die another 1/8 turn and try again with another test cartridge. Repeat, as necessary, until bolt closes without resistance. Save this setting.
Anything incorrect?
Click to expand...

That will work. No need to use another test cartridge, just use the same one until it fits.

A. I am not sure I understand the “shoulder setback” issues too well. I think I understand it after reading some of your posts, but when I read others, I’m lost again. To avoid confusing me further, please, rather than you providing me your own explanation, can anyone simply tell me what part of my OWN explanation is INCORRECT: If you screw the sizing die (full case) in too little, it will result in the shoulder of the case being set too high and if you screw the die in too much, it will result in the shoulder being set too low. Shoulders set too high and too low are not good, however some shooters like to go slightly high (for .308 and other cartridges that head space on shoulder) in order to make the cartridge fit a tad more snuggly in the chamber. Therefore a slightly high shoulder is OK and sometimes preferable, but a slightly low shoulder is not. Finally, if I do the above and also not allow the length of the case to exceed 2.015” (.308 Win), I should not have to worry about measuring headspace. How was that?
Click to expand...

That's fine.

B. Is it true that neck sizing dies do not affect shoulder setback because the only part of the case being sized is the neck? But, if you neck size a case that previously has a bad shoulder setback, it will still have a bad shoulder setback, right?
Click to expand...

Correct. If you have brass previously fired in a different rifle, you generally have to full length resize it to set back the shoulder to fit your rifle.

C. I understand that there are different opinions on whether to full size new brass (versus not) before neck sizing. Are the any good reasons for doing one versus the other?
Click to expand...

If the neck has a dent in it, then resizing the brass will straighten out the neck. Other than that, there is no need to resize new brass. Hope that helps.

Don
 
The .308 is headspaced on the shoulder datum, no matter what firearm it is chambered in. This is because it is a rimless case, even in a lever action. Fireformed cases will rechamber in a bolt action without full resizing of the case most of the time. I load several calibers with neck sizing only. Magnum cases headspace off the belt and full length dies will often overwork the brass unless the dies are set to just set the shoulder back to where the round chambers easily.
 
HEAD CLEARANCE
The distance between the head of a fully seated cartridge or shell and the
face of the breech bolt when the action is in the closed position. Commonly
confused with headspace."
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Thanks Bullet, I should have taken more time to clarify in my first post, most do not not hear much on Head Cllearance.
 
Commonly confused with headspace."
Click to expand...
We've been telling Bullet forever that everyone calls it headspace, so just give up and go with the flow, you know, like "embrace the horror" from the movie Armageddon, but he won't go for it. :D

Just kidding my buddy Bullet.............:)

This thread still going?

I certainly hope the OP got his questions answered. I think USSR finally cleared it up for him a few posts ago. :cool:
 
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