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Post by ET on Jun 21, 2019 11:11:22 GMT -5
Just thought I’d share on my take of evaluating a PT. Like most my first 2-visuals is Peak Pressure and resulting velocity. Nothing wrong with that. Then my attention goes to 3-other areas.  Rise This is just a measure of how fast peak pressure is obtained. IMO a good value is 100-120. Pressure Decline This basically shows the rate of pressure dropping from peak pressure. The slower the decline the more remaining pressure behind the bullet before it exits the bore. This means more resulting velocity. In this case 10K which is about 25% of peak pressure. Also, no trace of any secondary spike is seen. I won’t get into details about secondary spikes that IMO is not a good thing. Exit Point The red cross shows the point of bore exit. Below are little red OBT diamonds that represent where the calculated sweet spot is for a load. In this case a slight reduction in the main powder load could put you on the sweet spot. For this feature to work you need to know the exact bullet travel distance and input an outside source for muzzle velocity. If this was done in a 24” barrel it would not be an accurate representation in a different barrel length. Anyway, I hope something useful has been mentioned here. Ed |
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Post by billc on Jun 21, 2019 16:50:49 GMT -5
For my education, what are the variables used in the rise calculation? In this example trace the rise is 120, what are the units? Or is the rise term just an expression of "goodness"? Internal ballistics a very interesting subject and I could really geek out given half a chance. Thanks for a great post. Bill
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Post by ET on Jun 21, 2019 18:55:51 GMT -5
For my education, what are the variables used in the rise calculation? In this example trace the rise is 120, what are the units? Or is the rise term just an expression of "goodness"? Internal ballistics a very interesting subject and I could really geek out given half a chance. Thanks for a great post. Bill Bill this is taken from RSI. Rise (Rise Time) The rise time is calculated as the time (in microseconds) it takes for the pressure to rise from 25% of the peak value to 75% of the peak value. This can be taken as an indication of the "speed" to peak pressure. Efficient loads will normally have a faster rise time. It is also preferable to have a faster rise time because this helps ensure complete powder burn and reduced muzzle blast. If you want additional reading go to this web page and scroll down. www.shootingsoftware.com/pressure.htmEd |
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Post by billc on Jun 22, 2019 0:02:32 GMT -5
Thanks Ed! While I understood the concept of rise time -- the quicker to peak the better -- the units of microseconds and the 25% to 75% peak clarifies the concept and answers my question. I now understand and can have an informed opinion about this parameter. Bill
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Post by AJ on Jun 22, 2019 8:54:24 GMT -5
I would match rise time to what you are shooting. If you are shooting sabots, I would want a lower rise time to make the launch of the sabot slightly gentler. Even down to 80% is fine. Shooting land rider (smooth size) would want a higher rise time to get obturation to seal the gas blow by. Full Form size does not need a hard launch but it won't hurt them.
Another thing I watch is exit pressure. The higher the EP, the larger the muzzle blast is.
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Post by ET on Jun 22, 2019 11:16:41 GMT -5
I would match rise time to what you are shooting. If you are shooting sabots, I would want a lower rise time to make the launch of the sabot slightly gentler. Even down to 80% is fine. Shooting land rider (smooth size) would want a higher rise time to get obturation to seal the gas blow by. Full Form size does not need a hard launch but it won't hurt them. Another thing I watch is exit pressure. The higher the EP, the larger the muzzle blast is. AJ I feel I know what you want to express. Instead of lower, use longer and instead of higher use faster or shorter rise time. Then I would totally agree with your statements. Ed |
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Post by ET on Jun 23, 2019 5:44:24 GMT -5
Not trying to impress anyone with the smarts but felt a brief analogy of time relationship may help some better understanding Rise in the PT program.
Rise is measured in Time so the focus will be on Time.
Two men were assigned to complete a course. Man-1 did the course in 100seconds. Man-2 did the course in 120-seconds. So, who was faster?
Man-2 took 20% longer to complete the course. We could also phrase this as Man-2 was only 80% as fast as Man-1.
Hope this analogy is helpful to someone.
Ed
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Post by AJ on Jun 23, 2019 21:05:37 GMT -5
I would match rise time to what you are shooting. If you are shooting sabots, I would want a lower rise time to make the launch of the sabot slightly gentler. Even down to 80% is fine. Shooting land rider (smooth size) would want a higher rise time to get obturation to seal the gas blow by. Full Form size does not need a hard launch but it won't hurt them. Another thing I watch is exit pressure. The higher the EP, the larger the muzzle blast is. AJ I feel I know what you want to express. Instead of lower, use longer and instead of higher use faster or shorter rise time. Then I would totally agree with your statements. Ed Yes, I had my inverter hat on yesterday when I typed that. |
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