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Rifles, Reloading, Optics, Equipment
Reloading
Help me understand burn rate
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<blockquote data-quote="MagnumManiac" data-source="post: 2043900" data-attributes="member: 10755"><p>There is a major flaw in everyone's thinking when it comes to burn rate.</p><p>The simple fact of the matter is that burn rate, and how it is measured, are flawed, because case shape, size and volume as well as bore size all correlate to CHANGE the burn rate. Burn rate is NOT CONSTANT.</p><p>Some powders swap positions in burn and behave differently. Example, in the 338WM RE 22 SHOULD give higher velocities than RE 19, but due to Expansion Ratio, RE 19 with 225gr bullets is BEHAVING slower and producing higher velocity. A similar occurrence happens with the same powders in 30-06.</p><p>It was also noted some time ago that straight walled cases slow down the burn, so medium burn rate powders ACTUALLY behave much slower in these and provide the highest velocities.</p><p>A Calorimeter bomb is used to attain burn rates...why are they flawed?</p><p>The reason they are flawed, and I discussed this with the techs at ADI (makers of all Extreme Hodgdon powder), is because there are ZERO set standards in the industry. All manufacturers use RQ numbers (Relative Quickness) to list their powder from fastest to slowest.</p><p>This is the kicker, being there is no standard, each powder maker chooses a powder in the middle, this may be IMR4895 for IMR, H4895 for Hodgdon, and given a RQ of 100. Then all other powder is measured in the same Calorimeter bomb and given a higher/lower number depending on whether is faster or slower than this.</p><p>What is measured in a Calorimeter bomb?</p><p>Absolute pressure (AMP), Time & Heat.</p><p>Now none of this correlates to a cartridge case or firearm. In fact the burn is completely different, as there is no barrel exit, it is just a container with measuring equipment attached and a confined amount of powder is detonated inside it.</p><p>When I worked at ADI, these tests, which are very expensive, were only undertaken ONCE on a new batch of powder to see how it stacked up to previous batches.</p><p>To be sold as Hxxxx, it HAD to be within 3% of ALL previous batches in Calorimeter results, which are different to actual pressures tested in a firearm.</p><p>If it didn't match this 3% variance, it became a bulk powder and sold to ammo manufacturers.</p><p>Now, I have a pressure trace which is a piezo strain gauge attached to the barrel above the chamber, it gives raw pressure data. I have seen swings of 10% with different batches of powder, especially with H4350, which is beyond a 3% variance, but this 10% difference DOES NOT occur in every cartridge that powder is used in...why?</p><p>BURN RATE IS NOT CONSTANT IS WHY.</p><p></p><p>Sorry for the long post, but this needs to be digested and understood if you want to understand how smokeless powder behaves. There is more to it, such as Progressive powder, Digressive powder and Regressive powder.</p><p></p><p>Cheers.</p></blockquote><p></p>
[QUOTE="MagnumManiac, post: 2043900, member: 10755"] There is a major flaw in everyone’s thinking when it comes to burn rate. The simple fact of the matter is that burn rate, and how it is measured, are flawed, because case shape, size and volume as well as bore size all correlate to CHANGE the burn rate. Burn rate is NOT CONSTANT. Some powders swap positions in burn and behave differently. Example, in the 338WM RE 22 SHOULD give higher velocities than RE 19, but due to Expansion Ratio, RE 19 with 225gr bullets is BEHAVING slower and producing higher velocity. A similar occurrence happens with the same powders in 30-06. It was also noted some time ago that straight walled cases slow down the burn, so medium burn rate powders ACTUALLY behave much slower in these and provide the highest velocities. A Calorimeter bomb is used to attain burn rates...why are they flawed? The reason they are flawed, and I discussed this with the techs at ADI (makers of all Extreme Hodgdon powder), is because there are ZERO set standards in the industry. All manufacturers use RQ numbers (Relative Quickness) to list their powder from fastest to slowest. This is the kicker, being there is no standard, each powder maker chooses a powder in the middle, this may be IMR4895 for IMR, H4895 for Hodgdon, and given a RQ of 100. Then all other powder is measured in the same Calorimeter bomb and given a higher/lower number depending on whether is faster or slower than this. What is measured in a Calorimeter bomb? Absolute pressure (AMP), Time & Heat. Now none of this correlates to a cartridge case or firearm. In fact the burn is completely different, as there is no barrel exit, it is just a container with measuring equipment attached and a confined amount of powder is detonated inside it. When I worked at ADI, these tests, which are very expensive, were only undertaken ONCE on a new batch of powder to see how it stacked up to previous batches. To be sold as Hxxxx, it HAD to be within 3% of ALL previous batches in Calorimeter results, which are different to actual pressures tested in a firearm. If it didn’t match this 3% variance, it became a bulk powder and sold to ammo manufacturers. Now, I have a pressure trace which is a piezo strain gauge attached to the barrel above the chamber, it gives raw pressure data. I have seen swings of 10% with different batches of powder, especially with H4350, which is beyond a 3% variance, but this 10% difference DOES NOT occur in every cartridge that powder is used in...why? BURN RATE IS NOT CONSTANT IS WHY. Sorry for the long post, but this needs to be digested and understood if you want to understand how smokeless powder behaves. There is more to it, such as Progressive powder, Digressive powder and Regressive powder. Cheers. [/QUOTE]
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