Is Specific impulse indicative of performance as a gun propellant?

AI Thread Summary
Specific impulse is a measure of propellant performance, with black powder at around 80 seconds and rocket candy reaching up to 130 seconds. However, simply substituting rocket candy for black powder in a cartridge based on weight alone does not guarantee equivalent performance due to factors like burn rate and pressure dynamics. Firearms have strict pressure limits influenced by the mass of the propellant and projectile, which must be considered for safe operation. Additionally, the concept of brisance explains why certain explosives, like TNT, are unsuitable as propellants despite their high specific impulse. Overall, specific impulse alone does not determine the effectiveness of a propellant in firearms.
Christofer Br
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Is it that what increases propellants' specific impulse makes it proportionally a more powerful gun propellant?
Black powder has specific impulse of around 80s, while rocket candy has up to 130s of specific impulse. Does that mean I could replace the propellant in a BP cartridge with 80/130 of the weight in rocket candy and obtain the same performance in an idealized gun? (as in without considering burnrate, peak pressure and pressure vs time dependence)
Or is it that what increases propellants' specific impulse isn't making it proportionally a better gun propellant?
 
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Internal pressure of a cartridge using different propellants is usually measured in cup - copper unit of pressure
Get a reloading manual at the library and see what this means. Firearms have upper limits on pressure, which is related to the mass of bp, mass of projectile, and resulting impulse.

Propellants/explosives have a property called brisance: https://en.wikipedia.org/wiki/Brisance
Which is related to your question - it explains why TNT is not used as a propellant. There is an attached table in a link at the bottom: nitrocellulose (gun powder) is way down the list.
 
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