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Measuring the "WEB" area of the case for pressure signs?

 
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  #1  
Old 12-02-2008, 08:14 PM
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Measuring the "WEB" area of the case for pressure signs?

I have heard of reloaders measuring the "web",checking for pressure signs on cases.I am interested in using this approach,but I don't know exactly where this area of the case is,and how the procedure works.I have heard it is the safest,and most accurate way of determining pressure signs.I was hoping there are some people here who knows how this method works,and could chime in with some good info. on it.
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Old 12-02-2008, 09:41 PM
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Re: Measuring the "WEB" area of the case for pressure signs?

KQ,
To measure case head expansion, you need a micrometer that reads to .0001" (1 ten-thousands of an inch). A normal .001" micrometer isn't accurate enough for this type of measuring.

You will also need to 'scarifice' around 5 cases per batch if they are rimless or belted. Rebated rims do not need this done.

To accomplish accurate readings, you need to index (draw a line across) the bottom of the cases with a felt tipped marker, and then at opposite ends as indicated by the indexing, you need to file off about .003" of the rim, very carefully so as not to touch the case body, this is so the jaws of the micrometer fit at the very rear of the case body just forward of the extraction cannelure, this is where the measurement is taken. If you have 'blade' type micrometers, you won't need to do this.

The procedure is to take your reading as described above, a few measurements at the same place is the most accurate, you can take a measurement with the case one way and then rotate it 180 degrees and measure again. Take note of your measurement. This measurement is to be taken BEFORE firing the case.
After firing the case, take another measurement at EXACTLY the SAME place on the case and record that measurement.
The difference between the 2 is the case head expansion; .5312" before firing and .5315", or .0003" larger, after firing.
I do this with 5 cases from the same batch for each load increment.
You should discard these cases after 3 firings, because work hardening can set in and give you erroneous readings. Always start with once fired (starting loads) brass, because the first deflection is already present.

It is a general rule that .0003"-.0005" is around 50,000cup, but I prefer to work off .00025" as maximum expansion allowed.
Once this is reached, I then reduce my loads so that no expansion, or only .0001" is detectable.

It must be noted, however, if ANY one case, from the same batch, shows expansion above .0005", the load is TOO HOT and you will need to reduce the charge back to the load that showed no expansion or only .0001" for safety. A change in ambient temp may cause the previous HOT load to go way over and ruin your day and firearm!
Hope this helps, if not, I suggest you buy the latest Speer Manual #13, which describes the same procedure.
Cheers.
MagnumManiac.
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Old 12-02-2008, 09:50 PM
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Re: Measuring the "WEB" area of the case for pressure signs?

Thanks for the info.,do you feel this is the best method for checking pressure signs?
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Old 12-03-2008, 04:36 AM
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Re: Measuring the "WEB" area of the case for pressure signs?

Quote:
Originally Posted by KQguy View Post
Thanks for the info.,do you feel this is the best method for checking pressure signs?
KQ,
Unless you own a pressure sensor as I do, I believe this is the only SAFE way of determining SAFE PRESSURES for your brass, it is not the rifle that you have to be concerned with, it is the safety of your brass cases that is important.
There are too many variables and inconsistencies when handloading. It is foolish to believe that primer appearance is an infallable measure to what is a safe load in any cartridge.
The only infallable sign of an over max pressure load is the appearance of an ejector/plunger mark on the head of your cases, it actually doesn't matter whether you have an overload or not, if this is present on even ONE case at that loading, it is too hot for that brass, the next step is a ruptured case, and a blown up rifle.
Until I got my pressure sensor, case head expansion was the only way I measured my handloads for the OPTIMUM SAFE LOAD available in that brass, it didn't matter whether the loads were in fact at maximum SAAMI pressure or not, they were compltetely safe in my brass and rifles, and in fact gave better performance, in most instances, than my buddies who loaded until they felt 'sticky' extraction, and backed off 2 gr of powder and called that their safe max.
Cheers.
MagnumManiac.
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Old 12-03-2008, 06:19 AM
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Re: Measuring the "WEB" area of the case for pressure signs?

Thanks for all the info.,I have never felt very confident checking for pressure signs by looking at primers,and extractor marks.
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Old 12-03-2008, 08:06 AM
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Re: Measuring the "WEB" area of the case for pressure signs?

You'll get every pressure sign in the world before getting in trouble. But watching web expansion can help you save brass from a life shortening standpoint.

On upward load changes I check & back off with significant step changes measured in front of the extraction groove. I just use a caliper for quick checks at the range. But this is with well formed brass that has FULLY SETTLED.
Some cartridges, some brass, and some accurate loads, produce changes different than others. So you have to take this into account and just get to know your brass..
For example, growth from a 223 is considerably different than same measured growth from a WSSM, -given the same pressures.
And after FL sizing, you can't go by any kind of before/after comparison.

It just comes down to a step change from what you normally measure, from fully fire-formed brass, as freshly pulled from a smoking chamber.
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Old 12-03-2008, 11:38 PM
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Re: Measuring the "WEB" area of the case for pressure signs?

I have overloaded allot of cases to see what happens.

A) The 10mm is the weakest case head. It has a large Boxer primer pocket and deep extractor groove, making a thin spot in the web that sees the radial expansion of gas pressure and axial compression of the case pushing against the the breech face.

B) The 1889 7.65x53m Mauser case head fitted with Large rifle Boxer primer pocket is stronger and good for ~ 62,000 psi for long brass life. There are many cartridges that use this; 22-250, 243W, 6mmRem, 250 Sav, 257 Roberts, 25-06, 260 Rem, 270, 7mm-08, 7x57mm, 280 Rem, 308W, 30-06, 8x57mm, 338 Federal, 338-06, and 35 Whelen.

C) The 6mmBR case head has Mauser dimensions, but uses a small rifle Boxer primer pocket. This makes the web so strong that the primer is the weakest link. A CCI450 magnum primer and a custom bushed firing pin allow the usable pressure to be very high.

What does it all mean?
In some cases, the web is the weak link, and loads must be adjusted for long brass life by monitoring the primer pocket growth to insure there are no loose primers. Other webs are built better.
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