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Belted Magnums--Headspace on Shoulder or Belt?

 
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  #15  
Old 07-22-2010, 12:01 PM
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Re: Belted Magnums--Headspace on Shoulder or Belt?

Any fired bottle neck case has expanded to fit the chamber in both diameter and length (to the shoulder) and shrunk back at least a thou in every dimension. Thus, there is no value in pushing shoulders back passed the fired location.

Control of shoulder length must be measured after firing and after resizing of course. That requires a precise gage of some kind; the RCBS Precision Case Mic, the Innovative Technologies rig or a Hornady/Sinclair tool that mounts on a precision caliper.

Fact is, real world permanant expansion and reduction of brass cases just isn't as precise as some seem to think possible. Small varitions of the alloy within individual cases and the amount of work hardening each case has experienced will typically cause shoulder length variations of as much as 3 thou, occasionally as much as 5 thou. When I read of people claiming to set shoulders back exactly .001", etc, I cringe because it simply isn't possible to be that precise.

Don't try to average those lengths to establish a target. The only practical way we can deal with that variation is to FL size our cases so the longest resized shoulders match the longest fired shoulders and let the shorter cases fall where they may.
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Old 07-22-2010, 01:04 PM
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Re: Belted Magnums--Headspace on Shoulder or Belt?

Quote:
Originally Posted by boomtube View Post
Any fired bottle neck case has expanded to fit the chamber in both diameter and length (to the shoulder) and shrunk back at least a thou in every dimension. Thus, there is no value in pushing shoulders back passed the fired location.

Control of shoulder length must be measured after firing and after resizing of course. That requires a precise gage of some kind; the RCBS Precision Case Mic, the Innovative Technologies rig or a Hornady/Sinclair tool that mounts on a precision caliper.

Fact is, real world permanant expansion and reduction of brass cases just isn't as precise as some seem to think possible. Small varitions of the alloy within individual cases and the amount of work hardening each case has experienced will typically cause shoulder length variations of as much as 3 thou, occasionally as much as 5 thou. When I read of people claiming to set shoulders back exactly .001", etc, I cringe because it simply isn't possible to be that precise.

Don't try to average those lengths to establish a target. The only practical way we can deal with that variation is to FL size our cases so the longest resized shoulders match the longest fired shoulders and let the shorter cases fall where they may.

Agreed thats why i measure every case when i resize while doing my BR reloading and another good reason to aneal. I have found while doing improved chamberings that they like as much as .005 bump. I was having vertical problems last year with my heavy gun and found out it was the bump. When forming it shot 4-5" groups all day at 1k. With .002 bump it went out to 10" almost then back down to 4-5" when i bumped .005. So i do believe there is some merit in making sure that the cases that match at least get shot together.
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  #17  
Old 07-22-2010, 01:56 PM
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Re: Belted Magnums--Headspace on Shoulder or Belt?

boomtube, I have to disagree with a couple of things. For background I reload for over 40 rifles of all makes and calibers and measure shoulder position with a Hornady Headspace Gauge (although it should be called a shoulder gauge)



you said that

"Any fired bottle neck case has expanded to fit the chamber in both diameter and length (to the shoulder)"

IME, it takes several firings for most cases to expand to fit the chamber. A typical set of measurements if you measure on the shoulder and neck size only would be (this on a 30-06)

new case - 2.040"
once fired - 2.0485" (then neck sized)
twice fired - 2.050" (then neck sized)
3 times fired - 2.051" (slight crush fit, neck sized)
4 times fired - 2.0515" (crush fit, neck sized then body sized)

Now this is a little bit too much headspace but the gun shoots extremely well and the cases create no problems.

You said

"Fact is, real world permanant expansion and reduction of brass cases just isn't as precise as some seem to think possible. Small varitions of the alloy within individual cases and the amount of work hardening each case has experienced will typically cause shoulder length variations of as much as 3 thou, occasionally as much as 5 thou. When I read of people claiming to set shoulders back exactly .001", etc, I cringe because it simply isn't possible to be that precise."

I have set my die and sized as many as 50 cases and had variation of shoulder position in the range of .001" or even less. I do keep my cases marked and sorted by how many firings they have been through so the work hardening is the same.

Now belted magnum cases vary greatly in the measurement on new cases vs once fired case expansion. This is a post 64 Winchester 264 win mag new case and once fired




that is .037" movement of the shoulder on the first firing! It would probably have wound up at close to .040" but I bought it for rebarreling anyway. But the headspace on that rifle before rebarreling was .006".
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  #18  
Old 07-22-2010, 02:45 PM
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Some Ideas on what you are saying...

The last time I looked at a chamber reamer it was fixed in dimensions just as a cut chamber is fixed in dimensions.

SAAMI measures belted magnums from the belt on Belted cases, from the datum line on the shoulder to the back of the case head on rimless cases, and rimmed cases are heaspaced off the depth of the rim.

If one measures off the shoulder to the case head on a belted case one would be using compounding numbers.

The measurement from the datum line on a belted case to the front of the belt is one measurment (not Headspace) and the measurment from the front of the belt to the back of the case head is the headspace measurment.

The distance from the datum line on a belted case is just one of the dimensions.

Dies for full length sizing of belted cases are made three ways.

1. One type sizes past the belt by being undercut at the mouth to pass over the belt.

2. The second type sizes to the front of the belt.

3. The third type are made to size short of the belt.

Number one and number two the dies is cut .0015-.002" short to accomodate for full length sizing. Number three relies on the person loading to adjust for the correct amount of sizing. Type three does not full length size the web of the case. This die requires a body die to full length size. There is a fourth type of die made for sizing belted cases and it uses a collet that is adjustable and/or has fingers that compress at the bottom of the case sizing the web area. It come in two forms an adjustable floating collet or a fixed collet and the die is adjustable with locking rings.

Again we are talking about terminology and measurements. There is a difference between case length and headspacing.

Headspacing is always headspacing and should not be confused with case sizing issues. I can't make it any clearer. I would suggest you read Wayne Van Zol's addition to Frank de Haus's book "THE BOLT ACTION RIFLE" 3rd edition. He gives as good of explaination of this as I know of being written anywhere.

I have been reloading ammunition for 45+ years and building rifles for about 40 + years. I would estimate that I have loaded 50,000 300 Win mags for myself and my customers over the years.

Nat Lambeth
Custom Guns and Amminition
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  #19  
Old 07-22-2010, 07:08 PM
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Re: Belted Magnums--Headspace on Shoulder or Belt?

I understand the OP's question to be with regard to reloading cases that have already been fired in the chamber of a belted magnum cartridge. And I understand the question to be - which is preferable:

1) Resize the case so that the shoulder of the chambered casing contacts the shoulder in the rifle chamber before the forward edge of the belt contacts the belt recess cut in the chamber or,

2) Resize the shoulder of the casing back further, until the forward edge of the belt makes contact with the belt recess cut into the rifle chamber before the shoulder of the casing can make contact with the shoulder cut in the chamber of the rifle.

Option #1 is preferable in order to increase case life, and to improve the centering of the bullet to the bore of the barrel.

The OP made it reasonably clear that he's not asking about how to set the headspace of a rifle chamber when cutting the chamber in the barrel with a chamber reamer.
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  #20  
Old 07-22-2010, 07:10 PM
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Re: Belted Magnums--Headspace on Shoulder or Belt?

"you said that ... "Any fired bottle neck case has expanded to fit the chamber in both diameter and length (to the shoulder)"

Woods, yes, but you read more into that than is there! I meant the case had been expanded to fit the chamber under the 50K plus PSI pressure, didn't mean it stayed fully expanded after a single firing! My point being that after the first firing all we NEED to do is restore the sized neck to the fired position and chambering will be fine. The Hornady case tools you show on your very nice B&S caliper is one of the ways it can be measured and done.


"I have set my die and sized as many as 50 cases and had variation of shoulder position in the range of .001" or even less. I do keep my cases marked and sorted by how many firings they have been through so the work hardening is the same."

You have had MUCH better fortune than I. Or anyone else I know.




BobbyL, I was specifically addressing the OP's question of how he should resize cases his belted magnum hunting rifle, nothing I said was meant to address BR shootin' or BR accuracy techniques. Nothing I said or intended to say about FL sizing for easy belted magnum chambering and long case life could possibly be a certain process for best accuracy, seems that's clearly a matter of experimentation for each rifle. Surely you aren't suggesting everyone will get best accuracy in every rifle simply by setting fired shoulders back 2 thou, even if it were possible for most of us to be that repeatable. ??

Last edited by boomtube; 07-22-2010 at 07:23 PM.
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  #21  
Old 07-22-2010, 08:05 PM
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Re: Belted Magnums--Headspace on Shoulder or Belt?

Quote:
Originally Posted by woods View Post
boomtube, I have to disagree with a couple of things. For background I reload for over 40 rifles of all makes and calibers and measure shoulder position with a Hornady Headspace Gauge (although it should be called a shoulder gauge)



you said that

"Any fired bottle neck case has expanded to fit the chamber in both diameter and length (to the shoulder)"

IME, it takes several firings for most cases to expand to fit the chamber. A typical set of measurements if you measure on the shoulder and neck size only would be (this on a 30-06)

new case - 2.040"
once fired - 2.0485" (then neck sized)
twice fired - 2.050" (then neck sized)
3 times fired - 2.051" (slight crush fit, neck sized)
4 times fired - 2.0515" (crush fit, neck sized then body sized)

Now this is a little bit too much headspace but the gun shoots extremely well and the cases create no problems.

You said

"Fact is, real world permanant expansion and reduction of brass cases just isn't as precise as some seem to think possible. Small varitions of the alloy within individual cases and the amount of work hardening each case has experienced will typically cause shoulder length variations of as much as 3 thou, occasionally as much as 5 thou. When I read of people claiming to set shoulders back exactly .001", etc, I cringe because it simply isn't possible to be that precise."

I have set my die and sized as many as 50 cases and had variation of shoulder position in the range of .001" or even less. I do keep my cases marked and sorted by how many firings they have been through so the work hardening is the same.

Now belted magnum cases vary greatly in the measurement on new cases vs once fired case expansion. This is a post 64 Winchester 264 win mag new case and once fired




that is .037" movement of the shoulder on the first firing! It would probably have wound up at close to .040" but I bought it for rebarreling anyway. But the headspace on that rifle before rebarreling was .006".
+1 Woods!! I think that everyone is mistaking headspacing with shoulder bumping. Headspacing is done at chambering and with belted magnums is done on the belt. Even though it is called a headspacing tool it is just a measurement tool to determinie shoulder bump and has no effect on headspace. That is why there are go and no go gauges used in chambering.
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