Pressures Vs. Velocity Question

daniellybbert

daniellybbert

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so Ive been looking through my re-loading books, and a question came to mind.
looking at a certain powder pushing a given slug at a given speed, and then another powder pushing the same slug at the same speed but at a lower pressure, both listed as max loads; obviously the highest pressure listed is within the saftey bounderies of the cartridge... so given that one fact, could i not push the powder of lower pressures up to the high pressure load, giving me more FPS than listed safely?
 
well, sure you could. A guy can try anything. Id suggest buying a chronograph, and a good set of shooting glasses.
 
Make sure both pressure listings are given in the same units. PSI and CUP are NOT the same, and though they're related, I haven't seen a function that defines their relationship well enough to do anything like a 'conversion' from one value to the other.

That said, swing away! Maybe keep some unguent on hand.
 
another thing to watch for is case capacity the lower pressure load could be close to capacity and filling it any more gets you into a compressed load where the pressures start to rise really fast
 
I am no expert here so take what I say with a grain of salt.

The differnce is not just peak pressure but the rate at which that pressure is achieved. The speed of burn is different with different powders. Hence even though the peak pressure may be the same the vellocity of a bullet may be different.

for safety stick to the limits of your reloading book

good luck
 
Like so many things, it's area under the curve (a little technical, but that's what it is). If you have a fast burning powder you need a high quick pressure to attain the same velocity that a slower burning powder will produce over a longer time. If you look at a graph of pressure vs time the area under the curve will be very close for two powders producing the same velocity with different peak pressures. Although both of these burning times are incredibly fast there is a measurable difference. LUP and CUP vs. PSI are very different pressure measurments and are not converted.

PSI Is a measure of instantaneous peak pressure, and LUP and CUP more accuratly represent the total area under the curve but not peak pressure.
 
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