Questions about mixing multiples

Harness the power of precision mixtures of pressurized flammable vapor. Safety first! These are advanced potato guns - not for the beginner.
yyt
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Tue Nov 08, 2022 4:21 am

With the same caliber and weight, how many times of mixing can achieve the kinetic energy of 7.67*39mm rifle bullet?
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jackssmirkingrevenge
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Tue Nov 08, 2022 9:46 am

Firearms generate tens of thousands of psi of chamber pressure, so if you keep the same caliber and projectile weight, achieving similar power is impractical with a hybrid.

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Using a 50x mix and a 30 inch barrel with approximately 2:1 chamber:barrel volume ratio, I got 619 ft lbs, which is impressive but still less than half of the energy of a 7.62mm AK bullet.

If however we increase the caliber to 0.73", the same as a 12 gauge shotgun, and increase projectile weight to 30 grams, I can use the same barrel length and a smaller chamber:barrel volume ratio (although with a larger total volume) to match AK power levels at "only" 30x:

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It's important to note that at these mix levels you need a very strong launcher construction, for the 30x is set disc failure at 3000 psi which is the working pressure of typical paintball/HPA bottles.
hectmarr wrote:You have to make many weapons, because this field is long and short life
yyt
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Wed Nov 09, 2022 2:11 am

In fact, I have used 12 times of pure oxygen and propane to accelerate a steel ball with a diameter of 10.5mm and a weight of 5g to 575m/s. According to the kinetic energy formula, this steel ball carries 800j of energy, which has far exceeded the kinetic energy of a 9mm pistol, so I think it is possible to surpass a rifle. The pressure doesn't seem to determine everything.
yyt
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Wed Nov 09, 2022 2:21 am

jackssmirkingrevenge wrote:
Tue Nov 08, 2022 9:46 am
Firearms generate tens of thousands of psi of chamber pressure, so if you keep the same caliber and projectile weight, achieving similar power is impractical with a hybrid.

Image

Using a 50x mix and a 30 inch barrel with approximately 2:1 chamber:barrel volume ratio, I got 619 ft lbs, which is impressive but still less than half of the energy of a 7.62mm AK bullet.

If however we increase the caliber to 0.73", the same as a 12 gauge shotgun, and increase projectile weight to 30 grams, I can use the same barrel length and a smaller chamber:barrel volume ratio (although with a larger total volume) to match AK power levels at "only" 30x:

Image

It's important to note that at these mix levels you need a very strong launcher construction, for the 30x is set disc failure at 3000 psi which is the working pressure of typical paintball/HPA bottles.
In fact, I have used 12 times of pure oxygen and propane to accelerate a steel ball with a diameter of 10.5mm and a weight of 5g to 575m/s. According to the kinetic energy formula, this steel ball carries 800j of energy, which has far exceeded the kinetic energy of a 9mm pistol, so I think it is possible to surpass a rifle. The pressure doesn't seem to determine everything.
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jackssmirkingrevenge
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Wed Nov 09, 2022 11:15 am

yyt wrote:
Wed Nov 09, 2022 2:11 am
The pressure doesn't seem to determine everything.
A 10.5mm projectile has 1.36 times the base area as a 9mm projectile, this means for example that if you have 1000 psi in the barrel, then there is 99 lbs pushing on the 9mm and 134 lbs pushing on the 10.5mm, so significantly more energy for the same pressure. If we simplify the calculation it means you can get the same force as the 9mm with 1000 psi using 750 psi for the 10.5mm.

Also note that a 9mm pistol and 7.62mm rifle have significantly different barrel pressures. This page has some typical pressure values for firearms and also a useful excel calculator you can download.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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