How exactly does this work?

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Scott Tschirhart
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How exactly does this work?

Post by Scott Tschirhart »

I've been playing with powders in my .44 Special revolvers and an 1873 Cimmarron carbine.

I love the old Skeeter load, 7.5 gr of Unique under a Keith bullet and those balistics (900-980 fps depending on barrel length) are more than enough to do anything I need to do with the cartridge.

However, I note that there are some powders now that get those velocity levels with much less pressure. For example, Brian Pearce reports that 8 gr of Power Pistol gets 980 fps but stays under 15,500 psi but 6.9 gr of Unique is maximum for this pressure.

In my mind, a bullet in a revolver is a piston and the more pressure, the more velocity, all things being equal. However, this does not appear to be the case.

Does anyone understand how one can get the velocity out of Power Pistol with the significantly reduced pressure?
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Ray
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Re: How exactly does this work?

Post by Ray »

Ballistics is supposed to be just science but for our purposes and intents it can be a bit ornery.

https://leverguns.com/articles/ballisticians.htm
Last edited by Ray on Mon Oct 11, 2021 1:33 pm, edited 1 time in total.
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JimT
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Re: How exactly does this work?

Post by JimT »

Mic would be the guy to call.
He has forgotten more than most folks ever learned.
Call when you have some time to listen for a while.
Take notes.
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Re: How exactly does this work?

Post by Rusty »

2400 has always been my go to.
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AJMD429
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Re: How exactly does this work?

Post by AJMD429 »

Just guessing, but I think if the rate of burn is just right get the bullet moving and keep accelerating you get the least pressure spikes. Think of three or four people trying to push an automobile if they all push pretty hard at the right pace they'll get the car moving and nobody has to push that hard but if they were to all run against the car really hard and slam into it at the same time trying to push it, there would be 'pressure spikes' maybe manifesting as somebody spraining a wrist or back.
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OldWin
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Re: How exactly does this work?

Post by OldWin »

I try and factor pressure into my loads too. Especially with older original guns.
Lots of voodoo there. I find it very interesting. It was the basis for my switch to W748 from IMR3031 in the 30-30. As close as it is dimensionally, the 32WS still gets IMR. Pressure is much lower. Many times I think it's changed drastically by the slightest change in the combination of bore diameter, twist rate, and obviously burn rate.
If I tend to overlook it, it is with Unique. It is such a universal powder that I use it as a baseline to evaluate many cartridge/bullet combinations.
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Old No7
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Re: How exactly does this work?

Post by Old No7 »

AJMD429 wrote:
Wed Oct 13, 2021 4:47 am
"Think of three or four people trying to push an automobile if they all push pretty hard at the right pace they'll get the car moving and nobody has to push that hard but if they were to all run against the car really hard and slam into it at the same time trying to push it, there would be 'pressure spikes' maybe manifesting as somebody spraining a wrist or back."
Interesting analogy. That makes sense and was along the lines of what I was thinking, but I couldn't put it into words.

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marlinman93
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Re: How exactly does this work?

Post by marlinman93 »

Of course all powders have different burn rates, but even if they're side by side on the burn rate chart, they can still be very different. How the powders ramp up, or spike also affects what is maximum with one powder, yet just average with another.
Chamber pressures can vary immensely from powder to powder based solely on how fast they burn, and the way they spike up during the burn process.
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Scott Tschirhart
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Re: How exactly does this work?

Post by Scott Tschirhart »

We got a long explanation from Mic, but I am still trying to decipher it. Fascinating though.
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Grizz
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Re: How exactly does this work?

Post by Grizz »

marlinman93 wrote:
Wed Oct 13, 2021 11:23 am
Of course all powders have different burn rates, but even if they're side by side on the burn rate chart, they can still be very different. How the powders ramp up, or spike also affects what is maximum with one powder, yet just average with another.
Chamber pressures can vary immensely from powder to powder based solely on how fast they burn, and the way they spike up during the burn process.
this was my guess. the time element.

I make powder choices based on the least amount of pressure necessary to get the results I want, I call it downloading, but it can be seen in the ballistic charts.

looking forward to a complete explanation. it would be very helpful to know more about it.
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AJMD429
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Re: How exactly does this work?

Post by AJMD429 »

.

Although in general I like to be as informed as possible about anything I do, sometimes thinking about reloading is so scary it makes me not want to do it...! So MANY unknowns and uncontrollable variables.
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Scott Tschirhart
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Re: How exactly does this work?

Post by Scott Tschirhart »

AJMD429 wrote:
Thu Oct 14, 2021 5:35 am
.

Although in general I like to be as informed as possible about anything I do, sometimes thinking about reloading is so scary it makes me not want to do it...! So MANY unknowns and uncontrollable variables.
Really? I've been loading since I was 14 years old and the only mishap I have ever experienced was popping a primer (which occasionally happened with the old Lee Loaders). It was disturbing to say the least!
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marlinman93
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Re: How exactly does this work?

Post by marlinman93 »

I run into the issue of unknowns so often with my obsolete cartridges, and smokeless powders, that it's become common place for me to try to figure out what I can use, and what is safe in numerous old cartridges. Powder burn rates, how they spike, or how gradual they get to max pressure are very important to know.
But also as important is the effect certain powders have in various size cases, and whether the case is a bottleneck, or a straight wall design. If I took load data for a straight wall .45-70, decided to use it for my .44-77 Sharps Bottleneck, I could quickly get into trouble. The same charge that isn't an issue in the .45-70 could be a big issue in the .44-77 BN case.
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3leggedturtle
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Re: How exactly does this work?

Post by 3leggedturtle »

Gonna sidetrack a little bit with small caliber rifle. My favorite 223 load is 11.5grs BluDot with 50gr SP. It averages 2750fps out if a 20" barrel. Also do 9.4grs BluDot with 34gr HP. Havent chronied this one but it very quiet out of rifle and very mild out of a 10" Contender.
30/30 Winchester: Not accurate enough fer varmints, barely adequate for small deer; BUT In a 10" to 14" barrelled pistol; is good for moose/elk to 200 yards; ground squirrels to 300 metres

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crs
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Re: How exactly does this work?

Post by crs »

If you measure the pressure of a load and then view or print the pressure curve, much of the mystery will go away. Pressure Trace II is one such tool for capturing, displaying, and analyzing the pressure data.
Most references to pressure are to the PEAK pressure of the load, and not the energy of the load.
Many, if not most smokeless powders have a sharp pressure peak that quickly drops off.

One powder and possible others burn in such a way that there is no sharp pressure peak and rapid fall off. That pressure curve has no sharp peak, but has a slower and smoother rise and fall, and more of an elliptical shape and more energy under the curve. That energy propels the bullet down the barrel and out to it's destination. If you have never seen such graphs, I may be able to post a couple as examples.

PS If all this is old hat to you, my apologies for wasting your time.
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marlinman93
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Re: How exactly does this work?

Post by marlinman93 »

crs wrote:
Thu Oct 14, 2021 12:42 pm

Many, if not most smokeless powders have a sharp pressure peak that quickly drops off.

One powder and possible others burn in such a way that there is no sharp pressure peak and rapid fall off. That pressure curve has no sharp peak, but has a slower and smoother rise and fall, and more of an elliptical shape and more energy under the curve. That energy propels the bullet down the barrel and out to it's destination. If you have never seen such graphs, I may be able to post a couple as examples.
I've never owned a pressure tester. I use either old loading manuals from the early 1900's, or I call a friend who has Quickloads and ask him to run all the specifics through his program. I need to order Quickloads myself, as it not only takes in consideration case, powder, and bullet weight. But also takes into consideration barrel length, rifling twist rate, and other pertinent info to give a velocity, and chamber pressure.
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