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Calculating Barrel Pressure & Projectile Velocity (Read 11358 times)

KenHo Junior Member Offline Posts: 81 Joined: Jun 29^th, 2015	Re: Calculating Barrel Pressure & Projectile Velocity Reply #15 - Oct 29^th, 2015 at 9:27pm	Print Post
	Yep, While reviewing the spreadsheet at very beginning it just felt too good to be true to predict pressure or velocity based solely on chamber pressure. Here's a webpage with some good info showing just how much pressure can change just by changing brand of primer. Velocity does change, but not nearly as much as chamber pressure: (You need to *Login* or *Register* to view media files and links) Ken H>

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John Boy Ex Member	Re: Calculating Barrel Pressure & Projectile Velocity Reply #16 - Oct 29^th, 2015 at 9:53pm	Print Post
	Using the posted spreadsheet, I cranked in the numbers for a chrongraphed load for a 44WCF Ballard reload that calculated to 969 fps average with 10 readings. The spreadsheet pressure calculation was low and didn't seem correct


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KenHo Junior Member Offline Posts: 81 Joined: Jun 29^th, 2015	Re: Calculating Barrel Pressure & Projectile Velocity Reply #17 - Oct 30^th, 2015 at 10:08am	Print Post
	I wrote to tech support of the company that put out the spread sheet and got a nice detailed response. He says "typical factory loads it seems to work pretty well" and when plugging in numbers from "typical" factory loads it does seem to work pretty good. He when on to say "Extremely fast or really slow rounds may fall out of the sweet spot" and I think he means our BP type cartridges also. Good discussion on this and in researching the idea of pressure vs velocity I've learned a good bit. Great group of folks here - thanks to all for input. Ken H>

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KenHo Junior Member Offline Posts: 81 Joined: Jun 29^th, 2015	Re: Calculating Barrel Pressure & Projectile Velocity Reply #18 - Oct 30^th, 2015 at 11:05am	Print Post
	I asked permission to post the email here and received permission, so here's what they had to say: ***************************** All I can say is that the calculations are based on pure Physics. They uses mass, acceleration, force, and energy to derive a solution. Basically, starting with Isaac Newton’s Second law of motion and deriving a set of equations for gun systems. Everything else including the load type, configuration of the projectile, black powder or smokeless powder, and barrel rifling would affect the results. That is why I modified the final derived formula with a correction factor to take into account projectile friction, rotational energy, and heat transfer so that the obtained velocity and pressure values would closely represent real world factory load values. It is not a perfect real world solution but seems to work for a variety of calibers as shown in the example data. Extremely fast or really slow rounds may fall out of the sweet spot for the spreadsheet calculations, but for your typical factory loads it seems to work pretty well. The proportional relationship of projectile friction, rotational energy, and heat transfer for the factory loads all seem to be roughly the same. This is why all the calculations for the example rounds appear correct. All the items you mentioned in your questions can affect the current “as is” calculations and therefore may require a new modified correction factor to make the calculation mimic real world values. You would need to obtain experimental data / results in order to derive a new correction for factor the proportional relationship of projectile friction, rotational energy, and heat transfer. Once you do, then you can modify the spreadsheet formulas using the new correction factor so that the new calculations can closely mimic your real world values. ************************ I considered it a good response, and with some work I'm sure it would be adapted to BP cartridges with light or heavy loads. This work would require access to a pressure testing and chrono results. Ken H>

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calledflyer Frequent Elocutionist Offline Posts: 4036 Joined: Mar 9^th, 2015	Re: Calculating Barrel Pressure & Projectile Velocity Reply #19 - Oct 30^th, 2015 at 11:26am	Print Post
	Sure, you can make any set of statistics suit your wishes if you make exceptions, reassess the parameters, include only the things that fit your theory, etc. Hell, I don't much like anything but empirical things that I've seen for myself- but, I still remember both of these, too---- Don't believe everything you read. And, don't believe everything you see.


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RoyB Oldtimer Offline Posts: 851 Location: Dartmouth, MA Joined: Mar 28^th, 2011	Re: Calculating Barrel Pressure & Projectile Velocity Reply #20 - Oct 30^th, 2015 at 4:42pm	Print Post
	Strain Gauges....Wouldn't it matter how thick the barrel was over the chamber and what type of metal the barrel was made of. Would seem to me, the stronger/thicker the barrel, the less influence it would have on a strain gauge...No?

	Roy B Dartmouth, MA (You need to *Login* or *Register* to view media files and links)
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KenHo Junior Member Offline Posts: 81 Joined: Jun 29^th, 2015	Re: Calculating Barrel Pressure & Projectile Velocity Reply #21 - Oct 30^th, 2015 at 5:26pm	Print Post
	I fully expect the thickness of barrel and type of metal would certainly enter into one of the parameters that would be entered into the program for the strain gauges.

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RoyB Oldtimer Offline Posts: 851 Location: Dartmouth, MA Joined: Mar 28^th, 2011	Re: Calculating Barrel Pressure & Projectile Velocity Reply #22 - Oct 30^th, 2015 at 5:32pm	Print Post
	I'm going to attempt to get a copy of the operations manual.

	Roy B Dartmouth, MA (You need to *Login* or *Register* to view media files and links)
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RoyB Oldtimer Offline Posts: 851 Location: Dartmouth, MA Joined: Mar 28^th, 2011	Re: Calculating Barrel Pressure & Projectile Velocity Reply #23 - Oct 30^th, 2015 at 5:41pm	Print Post
	From the RSI site about barrel steel: My barrel is stainless, does that make a difference? The documentation for PressureTrace specifies the system "should" be calibrated with a load of known pressure. This is to help ensure pressure calculations are correct even if barrel dimensions are off slightly, the gage is glued slightly "askew" and there are metallurgical differences in the barrel steel. There are two key numbers used to calculate pressures. They are called Young's Modulus of Elasticity and the Poisson's Ratio. Young's Modulus of Elasticity: Within the limits of elasticity, the ratio of the linear stress to the linear strain is termed the modulus of elasticity or Young's Modulus and may be written Young's Modulus, or E =(Stress/Strain) It is this property that determines how much a bar will sag under its own weight or under a loading when used as a beam within its limit of proportionality. Poisson's Ratio: If a square bar is stressed in a testing machine in the direction of its length so that the length increases, there is a contraction in each opposite direction, which produces a decrease in the thickness of the bar. The ratio between the contraction at right angles to a stress and the direct extension is called the Poisson's ratio. For typical barrel steels the Modulus of Elasticity will fall between 29000 and 30000 ksi with the Poisson's Ratio between .290 and .305. Unfortunately there is no way a shooter can easily determine the metallurgical properties of his barrel. Even the manufacturer may not have accurate values. To be safe and provide reasonable results, PressureTrace uses 30000 ksi for the Modulus of Elasticity and .30 for the Poisson's ratio. How does this translate? The most common steels used to make barrels are 4140 Chrome-Moly (around 29700 ksi with P.R. of .290) and 416R Stainless (roughly 29000 ksi with P.R. ranging between .290 and .305). If a Remington 700 30-06 produces a peak pressure of 63254 PSI using PressureTrace; changing the Modulus of Elasticity to 29700 ksi will produce a calculated pressure of 62665 PSI. If a Poisson's Ratio of .29 (instead of .30) is also used for the calculations, the pressure becomes 62323 PSI or for a difference of 931 PSI. This only represents a +/- .75% difference. For stainless steel barrels, changing the Modulus of Elasticity to 2900 ksi will produce 61292 PSI; or a difference of 1962 PSI. Changing Poisson's Ratio to .29 from .30 will reduce the pressure calculation to 60960 PSI; h

	Roy B Dartmouth, MA (You need to *Login* or *Register* to view media files and links)
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RoyB Oldtimer Offline Posts: 851 Location: Dartmouth, MA Joined: Mar 28^th, 2011	Re: Calculating Barrel Pressure & Projectile Velocity Reply #24 - Oct 30^th, 2015 at 5:42pm	Print Post
	Sooooo....Where would we get "loads of known pressure"..?

	Roy B Dartmouth, MA (You need to *Login* or *Register* to view media files and links)
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RoyB Oldtimer Offline Posts: 851 Location: Dartmouth, MA Joined: Mar 28^th, 2011	Re: Calculating Barrel Pressure & Projectile Velocity Reply #25 - Oct 30^th, 2015 at 5:51pm	Print Post
	PRESSURE! (You need to *Login* or *Register* to view media files and links) Check out the SAMMI pressure for the 454 Casull and the 460 S&W....Yikes! 65,000psi! Here is rifle pressures: (You need to *Login* or *Register* to view media files and links)

	Roy B Dartmouth, MA (You need to *Login* or *Register* to view media files and links)
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KenHo Junior Member Offline Posts: 81 Joined: Jun 29^th, 2015	Re: Calculating Barrel Pressure & Projectile Velocity Reply #26 - Oct 30^th, 2015 at 6:00pm	Print Post
	A gentleman on another forum noticed the spreadsheet used "max peak" pressure rather than "area under the pressure curve. Reading from the email msg I posted above: The spreadsheet does say "Since average pressure closely represents the max Peak Pressure (formula), you can use Peak pressure to obtain Velocity". OK, remember in the email msg it was stated "Extremely fast or really slow rounds may fall out of the sweet spot for the spreadsheet calculations, but for your typical factory loads it seems to work pretty well" so I expect he found that "normal" factory loads used a "middle of road" speed smokeless powder where the peak pressure does come fairly close to representing the average pressure allowing the spreadsheet to work pretty good. Let's see if I'm understanding more here: the area under the pressure curve should come pretty close to determining velocity regardless of type of powder, fast or slow smokeless, or black powder - is that correct? A fast smokeless with a high peak max pressure vs a slow smokeless powder with much lower peak max pressure, but a longer pressure curve giving the same area under the pressure curve, both would have the same velocity - is that correct? If the above is correct, I'll bet with some work using strain gauges it would be possible to do a little work on spreadsheet to include the "quickness" value of powders and make it come real close to give true velocities and pressures. Shucks, I'm wanting to add so many inputs it would just be like Powley's computer.... a good thing Roy - get "us" the whole system - just call it an early Christmas Thanks to all for input - I'm still learning this stuff. Ken H>

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KenHo Junior Member Offline Posts: 81 Joined: Jun 29^th, 2015	Re: Calculating Barrel Pressure & Projectile Velocity Reply #27 - Nov 1^st, 2015 at 7:50pm	Print Post
	An update on the spreadsheet. Sam, the gentleman who created the spreadsheet has added a bit to it. You might wish to try it again. It has a dropdown to select caliber of choice, and a space for a correction factor. The default correction factor is 0.25 which is for normal factory loads. A different factor could be used for black powder, fast smokeless or slow smokeless powders. BUT - there is no guidance for what these values should be - those things will have to be determined thru experimentation. (You need to *Login* or *Register* to view media files and links) The webpage looks the same, you'll have to download spreadsheet to see changes. Ken H>

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