Headspace Variance

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rem6mmbr

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I measured my fired cases with a Hornady headspace guage and found that my headspace varies by 0.003. The cases have been fired 3 times. I'm new to BR, but I assume that this variance can't be helping accuracy. My question are: Why do I have this variance, what do I need to do to reduce it and what is the normal variance, if any. Thanks.
 
Make sure,

you are not measuring on the spent primer as they may be backed out somewhat depending on your load. Also is this fire forming brass as the dimensions will change until fully blown out?
 
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One peice of brass may expand slightly different than the next (longer or shorter) The only true way to check Headspace is with a steel gauge. If your checking fired and then sized cases, there could be a difference just by the nature of the brass. The headspace of your rifle will not change as you fire it. When I have cases that are not the same length after sizing, I simply run them back through the die and re-check, most of the time that will correct any sizing differences.
 
The primers are out

however, the brass has never been sized other than for the neck. I thought fireforming them would make them consistent. What is the proper method for achieving uniform headspace?
 
If it is brass that is fired three times in the same rifle with no full length sizing and you have only knocked out the primers before measuring I'd guess that the problem lies in the actual taking of the measurements rather than variations in the brass itself.
 
Measuring headspace can be a bit difficult. It requires measuring between a flat surface and a tapered surface, and the more shallow the taper is - the harder it is to get consistant readings. Your case heads need to be perfectly square to the centerline of the case, or you may get different readings as you rotate the case and measuring it again. You also need the ability to "feel" the tension when taking measurements, and your measuring device needs to be 100% solid and reliable.

- Innovative
 
I disagree

With the proper tools, measuring the headspace and shoulder bump is rather easy.
That is, with the proper tools. Most Benchrest Shooters have a small piece of barrel drop with just the neck and shoulder portion of their chamber established, so they can ascertain measurements as small as .0005. This is how we controle our headspace so closely to a desired measurement.
I suspect you are using a faulty measuring technique. I am not familiar with the Hornady Tool, but I suspect that it suffers from the same malady that most massed produced tools that are intended for the masses does, in that it leaves something to be desired.........jackie
 
Go by FEEL

Take the fire control unit out of your bolt. Chamber some of the cases that have been shot and see how closing the bolt feels, one case to the other. This may tell you if you have a variation. Some folks like a very slight tightness just before the bolt is closed.

Some folks like to bump their shoulders back from that slight feel by .002 to .003 so that closing the rifle is easy. There is a lot to this! :eek:
 
jackie schmidt said:
With the proper tools, measuring the headspace and shoulder bump is rather easy.
That is, with the proper tools. Most Benchrest Shooters have a small piece of barrel drop with just the neck and shoulder portion of their chamber established, so they can ascertain measurements as small as .0005. This is how we controle our headspace so closely to a desired measurement.
I suspect you are using a faulty measuring technique. I am not familiar with the Hornady Tool, but I suspect that it suffers from the same malady that most massed produced tools that are intended for the masses does, in that it leaves something to be desired.........jackie
Click to expand...

Jackie I agree, the barrel drop tool is what I use and it is spot on for measuring Head Space.
 
The barrel drop tool is great for benchrest shooters, but for production barrels it wouldn't work to well due to the wide range of acceptable dimensions on production chambers, and they're only good for use on one specific caliber. I haven't seen the Hornady headspace tool yet, but I have used the Stoney Point tool with pretty fair success.

- Innovative
 
rem6mmbr said:
however, the brass has never been sized other than for the neck. I thought fireforming them would make them consistent. What is the proper method for achieving uniform headspace?
Click to expand...
How and how far down are you resizing the neck and decapping? You may be distorting part of the shoulder by neck sizing. If you are using the Hornady LNL headspace tool where it just contacts one finite line around the neck then distortion of the shoulder may cause this variance.

Strip the bolt, then as Pete says set the shoulder by feel. You want to just start feeling a slight drag as the bolt finishes closing.

Some will argue with the feel method, but what you feel is what the chamber feels as you load each cartridge and that is what counts.

https://www.hornady.com/shop/?ps_se...&category_id=4ffc0a8772783e83440ac87ed0c3ee5b
 
I'm one that disagrees with the "feel the bolt close" method, because more often then not, you're feeling the pressure ring - not the case shoulder. If you can feel the case chamber, you're putting excessive pressure on your bolt lugs. The leverage and camming pressure of your bolt has enough force to damage your bolt lugs over time. Even most benchrest shooters don't want to feel the bolt crush your case into the chamber.

- Innovative
 
Larry Willis said:
I'm one that disagrees with the "feel the bolt close" method, because more often then not, you're feeling the pressure ring - not the case shoulder. If you can feel the case chamber, you're putting excessive pressure on your bolt lugs.
- Innovative
Click to expand...
Larry, what I call the pressure ring is on the base of a flat based bullet. What are you calling a pressure ring? I am also talking about a stripped bolt..

Besides who said anything about "crushing" the case into the chamber???

If I didn't feel the case chamber, with a seated bullet, that is when I would worry. And if you do not feel a slight resistance, you have no idea of how much too short you may or not be.


Like I said above, a slight drag just as the bolt closes.
 
Jerry,
There are some good benchrest bullets that have a slightly expanded base, and this is also called the pressure ring. I was referring to the part of the case "just above" the web (solid part of the case). That's also called the pressure ring or expansion ring. Except for the neck, this is the thinnest part of most cases.

I've talked to a jillion shooters (mostly hunters) that try to emulate benchrest reloading techniques to get the last bit of accuracy. Sometimes benchrest reloading techniques don't apply very well to hunting or extreme long range shooters. When I hear shooters say "I like to feel the bolt close a little tight when chambering a round", it's usually because they're partially resizing, neck sizing or not resizing properly. The case shoulder isn't the only consideration when resizing tapered cases. I've seen many hard to chamber handloads that were actually headspacing on the tapered case walls.

I'm sure that many benchrest shooters like to have their rounds chamber while seating the bullets deep into the lands. This is sometimes a great idea for benchrest shooting, but it's another bad idea for most non-benchrest shooting.

- Innovative
 
Larry

Have you ever sectioned a case?? I have. Lots of them. Modern cases do not have a "thin" portion as you stated just forward of the web. In fact, most have a heavy internal radius that ends in a steady internal reverse taper toward the shoulder. I have never seen a new case that exibits what you are referring too. I have seen cases that were fired too many times under a excessive headspace condition develope a internal stress point at the spot you are referring too.
I do agree with you on the 'feel" thing. There is more than one thing that can cause a case to have resistance as it is chambered. However, a properly sized case will show resistance only if the headspace is negative.
Incidentally, since the originol poster said he was "new to BR", I assumed he was referring to a Benchrest Rifle, not a Factory Rifle with a production tolerance chamber........jackie
 
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Larry Willis said:
I've talked to a jillion shooters (mostly hunters) that try to emulate benchrest reloading techniques to get the last bit of accuracy. Sometimes benchrest reloading techniques don't apply very well to hunting or extreme long range shooters. When I hear shooters say "I like to feel the bolt close a little tight when chambering a round", it's usually because they're partially resizing, neck sizing or not resizing properly. The case shoulder isn't the only consideration when resizing tapered cases. I've seen many hard to chamber handloads that were actually headspacing on the tapered case walls.

I'm sure that many benchrest shooters like to have their rounds chamber while seating the bullets deep into the lands. This is sometimes a great idea for benchrest shooting, but it's another bad idea for most non-benchrest shooting.

- Innovative
Click to expand...
Larry, not trying to be snotty or rude but this is a benchrest forum, Centerfire Benchrest to be exact. Sizing fired cases by feel with a stripped bolt is the norm not the exception.
 
I have sectioned a few cases, (mostly the larger hunting calibers) and it's easy to see why case head separations always occur just above the web. My advice for rem6mmbr is to verify the accuracy of his measuring tool, and your advice is to consider using a barrel drop tool. To me, that sounds like good information for a benchrest shooter.

- Innovative
 
Larry

In a head separation, the failure will usually occur at the point just forward of the solid web because that is where the maximum pressure is, and that is the first "hollow" section that is exposed, not because the case is "thinner" there than spots on down the case. In fact, the metal gets quite heavy in prorportion as compared to on down the case toward the shoulder.
If you have seen large hunting cases that exibit some sort of weak spot after several firings, it was probably because the cases were sized too much, creating excessive headspace. As the case grips the chamber walls, the head is not allowed to seat against the bolt, and it will actually stretch right at the point you are talking about. This could cause the phenomina you are speaking of.
By I know of no manufacturer who delibertly places a "weak" point at that criticle position in the case.
Jerry, of all of the methods we use to determine such things as 'shoulder bump' and the like, the feel method is the least desireable. It is a good way to creat exccessive headspace. In fact, I advice all shooters to NOT use this method, as there are other factors that can render "false readings". Measuring with a suitable tool is the only accurate way to determine these criticle measurements.....jackie
 
Jackie,
I totally agree that this area of the case is thinned due to excessive resizing. In fact, factory ammunition always has to fit in every chamber in a given caliber (even the smallest), so that always contributes to the problem of thinning brass just above the web. Some of the cases that I've sectioned have also revealed that some manufacturers have quite different inside dimensions (originally not weak spots) and some manufacturers even have a considerably different inside radius just below this part of the case.

Getting back to benchrest . . . . I believe that rem6mmbr is not actually getting accurate measurements. His fired cases must be consistent. I believe the accuracy of his measuring equipment or his technique is his problem.

- Innovative
 
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