oz_lowrider
Member
Can anyone tell me where I can see some good images of primers when bullets are underloaded and overloaded, ie, pressures, low and high.
troubleshooting reloads
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Any comprehensive reloading manual by Speer, Hornady, etc will have pictures of primers that are showing signs of overpressure.
Under pressure generally isn't noticeable except in handguns where where very light loads will have flattened primers. You should know your loads though and have a good idea where they are regarding the maximum powder charge. Loads put together at the start level (-10% of max) are considered safe even with variable components. Observation of pressure signs in a start load would usually indicate the wrong powder being used or the wrong data.
Under pressure generally isn't noticeable except in handguns where where very light loads will have flattened primers. You should know your loads though and have a good idea where they are regarding the maximum powder charge. Loads put together at the start level (-10% of max) are considered safe even with variable components. Observation of pressure signs in a start load would usually indicate the wrong powder being used or the wrong data.
oz_lowrider
Member
Thanks for that. I've been reloading for some time now but I saw some fired cases at the range today and I've not seen primers look like anything I've loaded or in the manuals. I guess I'm looking for some colour pics with good detail as those B/W in manuals are pretty poor images. You know how great some of the internet images are that's what I was hoping to see.
snuffy
Member
Well, you can't "read" primers for guessing pressures. They're really poor indicators for pressure. So many factors contribute to how they end up looking after a load is fired.
A too low pressure load can mimic a severely flattened high pressure load, by re-seating the backed out primer when the case slams against the bolt face. Then there's the backed out primer that many see as a high pressure sign when the shoulder has been set back too far, then a low pressure load is fired where the front of the case grips the chamber, but there's not enough pressure to re-seat the primer.
We, as reloaders, have very few ways to measure pressure. Of course there's the pressure trace chronographs that require a strain gauge be taped to the chamber, but they're quite costly. And they don't really give PSI readings, they have to be calibrated to a factory load which is assumed to be max pressure.
The best guess to be made, is by use of a regular chronograph. Each increment of powder should result in a measured, same, increase in velocity. The manuals will tell you what the top velocity should be for each bullet, powder, primer, and case for the caliber/cartridge you're loading. Then, when you're getting close to max powder charge, you should see a reduction in the increase of the velocity per each increment/grain of powder. That's where max pressure is. Going over that will make little or no increase in velocity, it can even reverse, going lower.
Then there's reading case head expansion, or CHE. And there's pressure ring expansion, or PRE. This is getting long, so I won't go into that.
A too low pressure load can mimic a severely flattened high pressure load, by re-seating the backed out primer when the case slams against the bolt face. Then there's the backed out primer that many see as a high pressure sign when the shoulder has been set back too far, then a low pressure load is fired where the front of the case grips the chamber, but there's not enough pressure to re-seat the primer.
We, as reloaders, have very few ways to measure pressure. Of course there's the pressure trace chronographs that require a strain gauge be taped to the chamber, but they're quite costly. And they don't really give PSI readings, they have to be calibrated to a factory load which is assumed to be max pressure.
The best guess to be made, is by use of a regular chronograph. Each increment of powder should result in a measured, same, increase in velocity. The manuals will tell you what the top velocity should be for each bullet, powder, primer, and case for the caliber/cartridge you're loading. Then, when you're getting close to max powder charge, you should see a reduction in the increase of the velocity per each increment/grain of powder. That's where max pressure is. Going over that will make little or no increase in velocity, it can even reverse, going lower.
Then there's reading case head expansion, or CHE. And there's pressure ring expansion, or PRE. This is getting long, so I won't go into that.
The only example I have. Here is a picture of 3 fired .357 mag cases I took with the one on the left showing signs of pressure both flattened and a little cratering as shown in the 2nd picture close up of it. The other 2 cases are normal in appearance. The case on the left showing high pressure was picked up at a range and was not one of my reloads.
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rfwobbly
Member
That primer looks the way I feel on Friday evenings !!
oz_lowrider
Member
Thanks for all the info. I've had a lot to do with strain gauges and I fail to see how external expansion cold tell anything but movement in the metal. What you would need is to get the sensor inside the chamber and even then most strain gauges small enough to fit the space woundn't handle the pressures we are dealing with. Most measure mmHg and we're talking tens of thousands of lbs/ 2x". So to measure in the chamber would require a really special bit of engineering.
I'll look at the chronograph and max loads recommended in the manuals. The indicator of max perss/ max Vel sounds like a good indicator. I didn't realise beyond max velocitu could even lower.
The photo of the primer in the case is what I was looking for, in the first instance. By the look of that primer it's lost all it's rounded sholder and it's flat to the edges, surely max press.
There is no doubt a person can ask a question on this forum and get good informative answers.
If the spelling is poor it's due to new glasses not focused to this screen distance and I can hardly read it. Now I have to get a pair of glasses to use when on the PC, DAM.
I'll look at the chronograph and max loads recommended in the manuals. The indicator of max perss/ max Vel sounds like a good indicator. I didn't realise beyond max velocitu could even lower.
The photo of the primer in the case is what I was looking for, in the first instance. By the look of that primer it's lost all it's rounded sholder and it's flat to the edges, surely max press.
There is no doubt a person can ask a question on this forum and get good informative answers.
If the spelling is poor it's due to new glasses not focused to this screen distance and I can hardly read it. Now I have to get a pair of glasses to use when on the PC, DAM.
FROGO207
Member
Seems a lot of my friends that are starting to reload find "Glocked" brass and they question the rectangular firing pin stamped impression and think that it is over pressured. Because of the tapered chamber I guess it technically is slightly. I also will explain about the bulged brass and how to cure it if you really want to salvage the brass. Glocks!!!
snuffy
Member
OZ, few people realize that the chamber of just about any firearm acts like a balloon when a cartridge is fired in it. It HAS to expand, if it didn't/couldn't, it would shatter. Pressure causes the steel to flex, albeit a tiny amount, but flex it does. The strain gauge that's firmly affixed to the mid-back of the chamber measures this flex, feeds it to the chronograph to be displayed in units of pressure.
Pressure guns used by the industry actually have a hole in the middle of the chamber about half way between the base and neck. The brass is pierced, then the pressure of firing is directed against a piston that crushed a copper pellet. The pellet was then measured and converted into units of pressure or C.U.P. Now days, its converted into P.S.I.
rcmodel
Member in memoriam
Actually, Copper Crusher (CUP) measurement is seldom used today.
The modern method of pressure measurement is done with a transducer strain guage glued to the barrels chamber. It reads directly on a computer screen with an oscilloscope type trace in Pounds Per Square inch, or PSI.
http://www.oehler-research.com/ism83.html
This has resulted in ballisticians discovering pressure spikes in loads that were formerly deemed safe using the old CUP measuring method.
That further has resulted in some of the older load data being revised downward when they found out what was really happening with the more accurate transducer measurement method.
rc
The modern method of pressure measurement is done with a transducer strain guage glued to the barrels chamber. It reads directly on a computer screen with an oscilloscope type trace in Pounds Per Square inch, or PSI.
http://www.oehler-research.com/ism83.html
This has resulted in ballisticians discovering pressure spikes in loads that were formerly deemed safe using the old CUP measuring method.
That further has resulted in some of the older load data being revised downward when they found out what was really happening with the more accurate transducer measurement method.
rc
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