Calculating pressure: How?

Milsparro

Milsparro

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http://www.alliantpowder.com/reloaders/RecipePrint.aspx?gtypeid=1&weight=200&shellid=35&bulletid=62&bdid=181

What pressure is this load at? I did something similar, .452 200 gr cactus plains lead round noses over 5.25 grains unique and federal large pistol primers... seems safe enough in the old iron.

At 5.4 grains unique the same bullet goes clean through 4x4s... kicked more... I would really like to know what the pressure numbers look like, because that seemed pretty potent, but I am not sure. Not wanting to fire something like that again till I know what the pressure is around.

What is the formula behind calculating pressure from speed and bullet weight and type?
 
I don't think you can calculate pressure directly from powder charge and bullet weight. I think you have to use a pressure gun with either a piezo electric cell which measures resistance changes as a result of temporary distortion of the barrel or alternately with copper or lead crusher guages. Changes in the volume of a cartridge for example will change the burn rate and hence the pressure

cheers mooncoon
 
RSI Pressure Trace II is really the only way. I have thought about getting a setup to test .41 Colt reloads. I would need a custom barrel made for a Thompson Contender though as it does not work on revolvers.
 
BrotherRockeye said:
an internal ballistics app like "Quickload" will calculate pressures afaik...
Click to expand...

Yeah Quickload will calculate pressures, and if your input data is good then it will be a fairly close approximation. I think Quickload tends to over-estimate pressure a bit on small pistol cartridges.
 
You can't know the pressure without pressure testing equipment, but you can accurately estimate pressure by extralopating from known, published loads. Do this knowing that even published loads are estimates, as your own chamber and barrel, powder lot, atmospheric conditions and other variables will produce different pressures than what the tester recorded the day the testing was done.

What round is this for? 45 Colt? You don't say, and the link you shared doesn't reveal that.

If it is 45 Colt, then the pressure is well below 6K CUP, as the burn rate of Unique is similar to Hodgdon Universal, and Hodgdon lists 6.4 grs of that at 5,700 CUP.
 
All other things being equal:

Faster Powder burn rate increases pressure
larger powder charge increases pressure
larger case capacity reduces pressure
larger bullet diameter increases pressure
hard cast increases pressure
soft cast reduces pressure
increased bullet weight increases pressure
jacketed increases pressure unless comparing with hard cast
 
I can run it on quickload if you give me the details.

Looks pretty light:

5krk1s.jpg
 
Ok... that software seems kickass and it's just what I'd need... as I love to experiment with antique loads. I particularly like the idea of creating calculators for powder types, bullet weights, fps and pressures.

I've once built my own calculator in Excel for the 1892 French revolver cartridge (based on data collected on the net, backed by some math formulas) that I've passed around CGN way back when, but I think my estimates were slightly off (mainly due to a lack of data to create estimates from - the more data to average from, the more accurate the estimates for any given variable).


So... where can I download/buy Quickload from, please? This could prove to be exactly what I need...

:D


Edit: Never mind, found it... $150 USD. I thought the price would be a tad more "shooter-friendly", lol! But it looks like it's worth it... at least in the demo it does.
 
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I downloaded a demo and it actually lists .41 Long & Short Colt. I'll be getting it shortly.
 
mwjones said:
wooooah where'd you get the cast bullet data for quickload?!?
Click to expand...

It's fairly easy to create custom bullet data for any bullet that Quickload doesn't have listed.

Quickload is quite a valuable tool for reloading antique or obsolete cartridges. But like any tool it's only as good as the person using it. Good data in = good data out. Variance in seating depth of 0.1" can raise pressure by 30% in the smaller capacity revolver cartridges. Bore variance can induce another broad degree of error. If you enter accurate bore diameter, cross-section, and bullet data, you get accurate info out.
 
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