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Rifles, Reloading, Optics, Equipment
Reloading
Too much pressure in the 300 RUM?
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<blockquote data-quote="ricka0" data-source="post: 68133" data-attributes="member: 3086"><p>Brent Moffitt writes:</p><p>[ QUOTE ]</p><p>Firing over-pressured loads will only tell you that they are over-pressure, not by how much though. </p><p></p><p>[/ QUOTE ]</p><p>EXCELLENT Point - I was assuming I could just nudge it over the top - but I think you are right.</p><p></p><p> [ QUOTE ]</p><p> neither PT or the M43 require calibration. ... The thick and thin wall pressure vessel formulas used in the M43 and PT software are public knowledge. The modulus of barrel steel and brass are well known and each strain gage is calibrated before you get it with a known gage factor. The rest is pretty simple.</p><p></p><p>[/ QUOTE ] </p><p>Except you don't know the exact geometry of your receiver, exact modulus of barrel batch (altho I suppose that could be very accurately measured).</p><p></p><p>I know folks have calibrated their SG with a hydraulic press. It would be interesting to know how close they are. I have no evidence how far off they are, I'm just skeptical (being an applied mathematician where almost every measurement needs to be calibrated).</p><p></p><p>I totally agree that SAAMI loads are same or lower (I think lower) but that is a much simpler task - loads get erratic the closer you get to max pressure.</p><p> [ QUOTE ]</p><p>I have never seen factory ammo exceed SAAMI maximum average in any test that I've run </p><p></p><p>[/ QUOTE ] </p><p>agreed</p><p> [ QUOTE ]</p><p> nor have I seen the average pressure between rifles chambered for the same cartridge vary in pressure more than about 3 Kpsi. </p><p></p><p>[/ QUOTE ] </p><p>Now that's an excellent test I have never considered. Have you SG tested the same batch of ammo in different guns? I guess on conservative loads it's not too surprising, but when you bump up near the max the differences could get significant.</p><p> </p><p> [ QUOTE ]</p><p> Getting MV by using an "accurate" chrono will probably get you closer to actual max load than CHE will in most cases </p><p></p><p>[/ QUOTE ] </p><p>How so? All that will do is get you to the conservative max which is probably significantly below SAMMI max pressure. Would you say that's true given my excellent .0001 blade mic, marked brass and experienced measure-er (you not me /ubbthreads/images/graemlins/smile.gif)</p><p></p><p>Now you've got me spooked out of using CHE, measured bolt release force, primer inspection, etc and back to my old scout masters maxim (NEVER EXCEED PUBLISHED MAX LOADS).</p><p></p><p>Question:</p><p>Under safe loads the CHE during firing conforms to the chamber THEN springs back to less than .0001" of original (once fired) dimensions after pressure is released. When you exceed the elastic limits of the cartridge brass, it doesn't spring back. Is that how CHE measurement works?</p><p></p><p>Awesome info Brent - the mathematical skeptic in me still wonders - your probably right about this stuff.</p><p></p><p> <a href="http://www.jamescalhoon.com/primers_and_pressure.html" target="_blank">Discovering Maximum Load By Measuring Case Head Expansion</a></p></blockquote><p></p>
[QUOTE="ricka0, post: 68133, member: 3086"] Brent Moffitt writes: [ QUOTE ] Firing over-pressured loads will only tell you that they are over-pressure, not by how much though. [/ QUOTE ] EXCELLENT Point - I was assuming I could just nudge it over the top - but I think you are right. [ QUOTE ] neither PT or the M43 require calibration. ... The thick and thin wall pressure vessel formulas used in the M43 and PT software are public knowledge. The modulus of barrel steel and brass are well known and each strain gage is calibrated before you get it with a known gage factor. The rest is pretty simple. [/ QUOTE ] Except you don't know the exact geometry of your receiver, exact modulus of barrel batch (altho I suppose that could be very accurately measured). I know folks have calibrated their SG with a hydraulic press. It would be interesting to know how close they are. I have no evidence how far off they are, I'm just skeptical (being an applied mathematician where almost every measurement needs to be calibrated). I totally agree that SAAMI loads are same or lower (I think lower) but that is a much simpler task - loads get erratic the closer you get to max pressure. [ QUOTE ] I have never seen factory ammo exceed SAAMI maximum average in any test that I've run [/ QUOTE ] agreed [ QUOTE ] nor have I seen the average pressure between rifles chambered for the same cartridge vary in pressure more than about 3 Kpsi. [/ QUOTE ] Now that's an excellent test I have never considered. Have you SG tested the same batch of ammo in different guns? I guess on conservative loads it's not too surprising, but when you bump up near the max the differences could get significant. [ QUOTE ] Getting MV by using an "accurate" chrono will probably get you closer to actual max load than CHE will in most cases [/ QUOTE ] How so? All that will do is get you to the conservative max which is probably significantly below SAMMI max pressure. Would you say that's true given my excellent .0001 blade mic, marked brass and experienced measure-er (you not me [img]/ubbthreads/images/graemlins/smile.gif[/img]) Now you've got me spooked out of using CHE, measured bolt release force, primer inspection, etc and back to my old scout masters maxim (NEVER EXCEED PUBLISHED MAX LOADS). Question: Under safe loads the CHE during firing conforms to the chamber THEN springs back to less than .0001" of original (once fired) dimensions after pressure is released. When you exceed the elastic limits of the cartridge brass, it doesn't spring back. Is that how CHE measurement works? Awesome info Brent - the mathematical skeptic in me still wonders - your probably right about this stuff. [url="http://www.jamescalhoon.com/primers_and_pressure.html"]Discovering Maximum Load By Measuring Case Head Expansion[/url] [/QUOTE]
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Too much pressure in the 300 RUM?
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