Case head expansion
- Thread starter hayseed
- Start date
Yes there's a real easy way to do this. If you have a lathe knock out the primer and put the base on a dead head center . Then close the tailstock to it with another center. Then run a mag base indicator on the y-y across any part of the case or neck. Repetitive cases can be measured this way with good accuracy.
If you don't have a lathe, you'll have to make up some sort of fixture that will result in the same solution. They're not too hard to make but a good set of mics or verniers will get you pretty close if you can have repeatability from one case to another.
There's a million ways to do this right down to boring and reaming a tapered hole in some 1010 and then laying the verniers on the side and reading to the neck where it protrudes out the steel et ad nausem. Hope it helps
If you don't have a lathe, you'll have to make up some sort of fixture that will result in the same solution. They're not too hard to make but a good set of mics or verniers will get you pretty close if you can have repeatability from one case to another.
There's a million ways to do this right down to boring and reaming a tapered hole in some 1010 and then laying the verniers on the side and reading to the neck where it protrudes out the steel et ad nausem. Hope it helps
hey seed
I'm not sure why this should be a problem. You only need to do it to a small sample of cases and there are several ways to mark the cases.
I color the case head with a black magic marker, say about 3/8" or so. I then take a dial caliper, open it to around .200", place one leg of the caliper on the base and then make a scratch through the magic marker with the other leg. You can go completely around the case making a full circle. This mark will last through several firings if you are careful. If the mark is erased during re-sizing you can always duplicate it if you record it's loaction.
If you are going to take measurements above the solid head you can make a second ring there. With low pressure cartridges there may not be enough expansion at the solid head to show any differences in loads and measurements at the expansion ring will be a better indicator.
You really need a good micrometer with blade anvils to get a good reading. Of course, you need some sort of standard on which to base expansion and new factory loaded cartridges are best for this. Or start with a known handload on new brass.
Ray
I'm not sure why this should be a problem. You only need to do it to a small sample of cases and there are several ways to mark the cases.
I color the case head with a black magic marker, say about 3/8" or so. I then take a dial caliper, open it to around .200", place one leg of the caliper on the base and then make a scratch through the magic marker with the other leg. You can go completely around the case making a full circle. This mark will last through several firings if you are careful. If the mark is erased during re-sizing you can always duplicate it if you record it's loaction.
If you are going to take measurements above the solid head you can make a second ring there. With low pressure cartridges there may not be enough expansion at the solid head to show any differences in loads and measurements at the expansion ring will be a better indicator.
You really need a good micrometer with blade anvils to get a good reading. Of course, you need some sort of standard on which to base expansion and new factory loaded cartridges are best for this. Or start with a known handload on new brass.
Ray
Some good ideas there guys - thanks. I don't have a blade mic or lathe, but I should be able to scribe a ring pretty precisely and get some decent measurements off that.
I did section a case and have been giving some thought to where best to take my measurement. Would you think right where the base thins to body wall thickness or what?
It's a 6BR, and I did pick up a box of factory Lapua ammo to use as a baseline for comparison. Can't remember when I last bought a box of factory stuff, but I guess it's for a worthy cause. Dang, but Lapua is proud of their ammo. Do most of you that keep track of the expansion consider Lapua stout enough to be very near max?
Thanks again
I did section a case and have been giving some thought to where best to take my measurement. Would you think right where the base thins to body wall thickness or what?
It's a 6BR, and I did pick up a box of factory Lapua ammo to use as a baseline for comparison. Can't remember when I last bought a box of factory stuff, but I guess it's for a worthy cause. Dang, but Lapua is proud of their ammo. Do most of you that keep track of the expansion consider Lapua stout enough to be very near max?
Thanks again
CatShooter
I'm not sure that it's worth the effort.
When the fad of measuring case expansion started,back in the dark days of my "ute"), I went out and bought a top of the line Starrett Blade Micrometer that was calibrated to 0.0001". I was gonna "do it" right!
I did due diligence to the effort and came up with...
... nothing.
Here's why.
First - Most folks that have been loading for a while have come to realize that not all brass is of the same hardness.
It has been my experence that Winchester case heads are harder than Remington, and Remington is harder than Federal, and that Lapua is much harder than all of those American guys.
So for a given force, you will get varying amounts of "expansion".
So what does that expansion tell you??...
... nothing except that there's a bunch of pressure going on inside of the case - is it 40Kpsia, or 65Kpsia???
I donno - do you?
Second - Why 0.001" - why not 0.002" or 0.0006". Does the 0.001" have any meaning, or did the originator of this faux science pick 0.001" because his blade micrometer had calibrations of one thou ??...
... if so, thank god he didn't have 0.0001 calibrations, or we'd be running our cases at 10Kpsia? :lol:
Third - When do you measure it?? Before the first firing, after you have fired it, but before the first reloading?
It makes a difference, because brass crystal structure will make a first "settling" shift, then pretty much stop.
So... you have Lapua or Federal, and is the case new or fired, or fired three times, and what does the 0.001 thou mean.
If you decide you are going to be "smart" about it... you measure the new loaded round, thinking "Self, I'll out fox them, I'll measure the expansion on factory ammo, and then use that to judge my loads..." but brass will not expand the same on the second firing, so if the factory was 55Kpsia, your loads that cause the same expansion might be 65Kpsia :,
And last - can you take a unfired case, measure it, then,tomorrow) get the same measurement?? - and do the same thing for a week and get the same measurement each day...
... and what does it tell you?
Wanna buy a beautiful Starrett blade mic,if I can find it)?
,Now crawling back into my hidie hole
)
.
When the fad of measuring case expansion started,back in the dark days of my "ute"), I went out and bought a top of the line Starrett Blade Micrometer that was calibrated to 0.0001". I was gonna "do it" right!
I did due diligence to the effort and came up with...
... nothing.
Here's why.
First - Most folks that have been loading for a while have come to realize that not all brass is of the same hardness.
It has been my experence that Winchester case heads are harder than Remington, and Remington is harder than Federal, and that Lapua is much harder than all of those American guys.
So for a given force, you will get varying amounts of "expansion".
So what does that expansion tell you??...
... nothing except that there's a bunch of pressure going on inside of the case - is it 40Kpsia, or 65Kpsia???
I donno - do you?
Second - Why 0.001" - why not 0.002" or 0.0006". Does the 0.001" have any meaning, or did the originator of this faux science pick 0.001" because his blade micrometer had calibrations of one thou ??...
... if so, thank god he didn't have 0.0001 calibrations, or we'd be running our cases at 10Kpsia? :lol:
Third - When do you measure it?? Before the first firing, after you have fired it, but before the first reloading?
It makes a difference, because brass crystal structure will make a first "settling" shift, then pretty much stop.
So... you have Lapua or Federal, and is the case new or fired, or fired three times, and what does the 0.001 thou mean.
If you decide you are going to be "smart" about it... you measure the new loaded round, thinking "Self, I'll out fox them, I'll measure the expansion on factory ammo, and then use that to judge my loads..." but brass will not expand the same on the second firing, so if the factory was 55Kpsia, your loads that cause the same expansion might be 65Kpsia :,
And last - can you take a unfired case, measure it, then,tomorrow) get the same measurement?? - and do the same thing for a week and get the same measurement each day...
... and what does it tell you?
Wanna buy a beautiful Starrett blade mic,if I can find it)?
,Now crawling back into my hidie hole
).
CatShooter -
As usual you have some pretty valid points. It would be easy to end up chasing your tail here and making unsupported assumptions especially in regard to different brands of brass. However, by tightening up the parameters, I think a person could still end up with some usable info.
I just received an email reply from Lapua stating the pressure of 105 Scenar ammo specs at 58,760. I plan to mic it at the base and at the expansion ring area, both before and after firing. I recognize it would only revelantly compare to handloads using new unfired Lapua brass. Seems like an apples to apples deal to me.
Although I've never fired Lapua ammo before, I kind of expected it to be about 5k higher... From what I've read, some shooters are running quite a bit hotter to hit the upper vel node. Seems like this expansion might be a good tool along with the others to prudently ease up into the 60k range a ways.
I do wish I had a good blade mic. Say, CatShooter, how proud are you of that Starrett?
As usual you have some pretty valid points. It would be easy to end up chasing your tail here and making unsupported assumptions especially in regard to different brands of brass. However, by tightening up the parameters, I think a person could still end up with some usable info.
I just received an email reply from Lapua stating the pressure of 105 Scenar ammo specs at 58,760. I plan to mic it at the base and at the expansion ring area, both before and after firing. I recognize it would only revelantly compare to handloads using new unfired Lapua brass. Seems like an apples to apples deal to me.
Although I've never fired Lapua ammo before, I kind of expected it to be about 5k higher... From what I've read, some shooters are running quite a bit hotter to hit the upper vel node. Seems like this expansion might be a good tool along with the others to prudently ease up into the 60k range a ways.
I do wish I had a good blade mic. Say, CatShooter, how proud are you of that Starrett?
CatShooter
Hey Hayseed,is that a "pun" 
)?
Here's the thing.
Just cuz Lapua says it's 58Kpsia, doesn't mean doodley squat.
Some years back, SAAMI bought a batch of o-fish-ul calibrated loads of the same lot number and then sent them around to all the folks that load and/or test ammo - guys that had "real deal" setups and were using calibrated guns - using either copper crusher barrels, strain, or inertial proof guns.
They asked each recipient to fire the 10 rounds and report back the peak pressure - they left out the average pressure cuz the copper guys couldn't get those figures.
And the "range" of pressures that were reported back ran from 41Kpsia to 66Kpsia? WTF??
What is hard for most guys to accept is that these "scientific figures" are just edjamacated guesses.
In a given lab, they can reproduce their test loads pretty well, and can hold their standards pretty well - but their data is not transferable to the guys down the street.
The very best "practical" judgment of pressure is when your cases are starting to wipe the bolt face or show ejector marks - at that point you are just above YOUR absolute maximum pressure.
One very well known shooter,who everyone else bows to his feet) says increase until you see ejector marks and drop a 1/2 a grain.
Now - in my way of thinking, that is safe, but a little higher than I want to run my average riffles...
... I drop 3/4 of a grain -,HA! Just kidding).
I'm sure that 9,000 guys will disagree with me,they always do!), but I don't think there is a "maximum pressure, until you see some other effects - we all used to think "cratering" was it - it was the death note and you had to cut back - for beginners, I think it's not a bad limit or suggestion.
But after we shoot for a while, we realize that cratering can come from oversized pin holes, and/or weak pin springs.
And with more experence, we learn that flattened primers can,and most often do) indicate some headspace - not necessarily a bad chamber, but just a maximum chamber and minimum case will give you flattened primers at 50Kpsia,or less!) :, ...
... but all of us know that most "serious" long range shooters are now running cases at ~65Kpsia, and maybe a bit above.
So all I'm saying is don't reach for, and jump on, one magic indicator - use all of your wits and smarts, and integrate primer, ejector and other case signs to determine when you are "up there"!
...
.
)?Here's the thing.
Just cuz Lapua says it's 58Kpsia, doesn't mean doodley squat.
Some years back, SAAMI bought a batch of o-fish-ul calibrated loads of the same lot number and then sent them around to all the folks that load and/or test ammo - guys that had "real deal" setups and were using calibrated guns - using either copper crusher barrels, strain, or inertial proof guns.
They asked each recipient to fire the 10 rounds and report back the peak pressure - they left out the average pressure cuz the copper guys couldn't get those figures.
And the "range" of pressures that were reported back ran from 41Kpsia to 66Kpsia? WTF??
What is hard for most guys to accept is that these "scientific figures" are just edjamacated guesses.
In a given lab, they can reproduce their test loads pretty well, and can hold their standards pretty well - but their data is not transferable to the guys down the street.
The very best "practical" judgment of pressure is when your cases are starting to wipe the bolt face or show ejector marks - at that point you are just above YOUR absolute maximum pressure.
One very well known shooter,who everyone else bows to his feet) says increase until you see ejector marks and drop a 1/2 a grain.
Now - in my way of thinking, that is safe, but a little higher than I want to run my average riffles...
... I drop 3/4 of a grain -,HA! Just kidding).
I'm sure that 9,000 guys will disagree with me,they always do!), but I don't think there is a "maximum pressure, until you see some other effects - we all used to think "cratering" was it - it was the death note and you had to cut back - for beginners, I think it's not a bad limit or suggestion.
But after we shoot for a while, we realize that cratering can come from oversized pin holes, and/or weak pin springs.
And with more experence, we learn that flattened primers can,and most often do) indicate some headspace - not necessarily a bad chamber, but just a maximum chamber and minimum case will give you flattened primers at 50Kpsia,or less!) :, ...
... but all of us know that most "serious" long range shooters are now running cases at ~65Kpsia, and maybe a bit above.
So all I'm saying is don't reach for, and jump on, one magic indicator - use all of your wits and smarts, and integrate primer, ejector and other case signs to determine when you are "up there"!
....
CatShooter
hayseed said:
It's not that I'm so proud of it - it's a "finding" thingie
I load in the messiest sandbox in the world - my best friend said, "You make ammunition HERE???"
.
Dang CatShooter,
Here I thought I was going to be able to justify wasteing a bunch of time and if I played my cards right, buying a new precision measuring gizmo. You're a real wet blanket you know.
Since I already shelled out the 35 BUCKS for the ammo, guess I'll go ahead and keep track of the expansion along with the velocity. I hadn't intended to forsake all the other pressure indicators, but was sort of looking forward to being able to quantify an aspect of it...
I really am suprised by your report of variance in independent pressure gun tests. I thought it might vary a k or two. Well, I knew this expansion business wouldn't be an exact science. Guess whatever I do come up with will have to be taken with more than a grain or two of salt.
Thanks for your perspective.
Here I thought I was going to be able to justify wasteing a bunch of time and if I played my cards right, buying a new precision measuring gizmo. You're a real wet blanket you know.
Since I already shelled out the 35 BUCKS for the ammo, guess I'll go ahead and keep track of the expansion along with the velocity. I hadn't intended to forsake all the other pressure indicators, but was sort of looking forward to being able to quantify an aspect of it...
I really am suprised by your report of variance in independent pressure gun tests. I thought it might vary a k or two. Well, I knew this expansion business wouldn't be an exact science. Guess whatever I do come up with will have to be taken with more than a grain or two of salt.
Thanks for your perspective.
CatShooter
hayseed said:
Even with the same pressure gun, the same case the same "everything" pressure readings vary by 5 or 6 Kpsia - what you see printed out is an average.
Same as when you load - you weigh the cases, same gun, same powder lot, same bullet lot, and you get a ES of 100 fps,for hunting ammo in a standard chamber).
Take that same ammo and spread it around the country in guns with different chambers,of different ages and wear) in barrels with different riffling....
... aw you know! :lol:
.
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