Gas volume

[JohnH]

How much gas volume is created by the powder charge volume? Is there a linear relationship? I know that the pressure relationship is non linear, and that the over all pressure is dictated by the relationship between the powder volume and the case/chamber/barrel volume (the relationship between the case volume and the barrel volume is also called the expansion ratio) In the end of it, 5 grains of Unique will develop greater pressure in the 32 Mag case than it will in a 38 Special case, because the one has less volume than the other. I assume the gas volume would be the same but the lessor chamber volume will raise the pressure, and the increased expansion ration will make the pressure curve longer, but is there a relationship between the powder volume and the gas volume?

[Green Frog]

The gas volume and pressure are inversely related. The net product of the two should be a constant for a given mass of powder burned. If you put a full charge for a 44 mag in a BR 50 case, a lot of gas but little pressure will result. Put the same charge in a 357 mag case, and because the volume of the gas will be so restricted, pressure will be very high (probably until something let’s go!)

This is just my intuitive analysis based on a year of college Physics taken over a half century ago.

Froggie

[45-70 Chevroner]

If you go by the loading data in reloading manuals, the gas volume is of little importance. I truly think gas volume has very little to do with reloading. I am really sorry that I even got into this conversation.

[358429]

There must be some correlation between powder charge mass and volume, bullet weight and diameter and loaded cartridge internal powder volume

Reading manuals I have noticed similar load datas ( powder charges and bullet weights) with comparing cast bullet loads between 44 magnum and 308 Winchester.

3 grains of Tightgroup works in a lot of small cartridge cases.

20 grains of IMR 4227 Works in a lot of medium cartridge casings.

30-40 grains of IMR 3031 Works in a lot of medium to large rifle casings.

[Larry Gibson]

There must be some correlation between powder charge mass and volume, bullet weight and diameter and loaded cartridge internal powder volume.......

Basically correct with the addition of the expansion ratio factored in as also mentioned above.

[358429]

Yes internal ballistics.

[Larry Gibson]

How much gas volume is created by the powder charge volume? Is there a linear relationship? I know that the pressure relationship is non linear, and that the over all pressure is dictated by the relationship between the powder volume and the case/chamber/barrel volume (the relationship between the case volume and the barrel volume is also called the expansion ratio) In the end of it, 5 grains of Unique will develop greater pressure in the 32 Mag case than it will in a 38 Special case, because the one has less volume than the other. I assume the gas volume would be the same but the lessor chamber volume will raise the pressure, and the increased expansion ration will make the pressure curve longer, but is there a relationship between the powder volume and the gas volume?

Some powders, mostly of the extruded type, have linear relationship, i.e. as the charge of powder is increased the pressure does in crease in a linear manor....up to a point. The old Powley Computor and, to a large degree, Quickload computations are based on that.

[nhyrum]

Here's my thinking. The combustion is a sealed event. It does not really on outside oxygen to burn. So, because of the conservation of mass, 20 grains of powder cannot produce more than 20 grains of gas volume, by weight. If you need more gas, you need physically more powder. Pressure and burn efficiency are a different animal and can make that more or less not entirely true, but you can't have gas that wasn't there as powder to begin with. Where I see this is in my 9x25 Dillon open gun. I use h110 because it gives me the velocity I need, along with the amount of gas my compensator needs. Other powders can get me the velocity I need, and even at similar pressures, but with far less powder, which means less gas. Like 9 or 10 grains, where I use almost 18 grains h110

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[wmitty]

If we ask what volume of gas is produced for a specific mass of powder; don't we have to specify the pressure that the volume of gas is under? It's easy to visualize when we fire a .22 LR in a short barreled pistol with it's relatively high (and loud report) muzzle pressure as compared to the same cartridge being fired in a 24" barreled rifle with it's much lower (and quieter report) muzzle pressure. As the bullet travels down the rifle barrel, the volume of propellant gas is continuously increasing, while the pressure continuously decreases until abruptly dropping to atmospheric upon muzzle exit, with the propellant gas volume expanding violently to reach equilibrium with the atmosphere.

[358429]

https://m.youtube.com/watch?v=CgXz-njLLV4

[charlie b]

The gas produced by burning in simple form is based on the chemical composition of the powder. A certain amount of powder will produce a certain number of moles of gas. The volume of that gas is different based on other conditions.

For ideal gases the relationship is Press* Vol = moles of gas * Gas constant * Temp. You can see that as the volume goes up the pressure goes down, if everything else remains constant (which it does not).

Do not confuse this with burn rate, which is a different animal. The burn rate is also dependent on press and temp. As the burning progresses the moles of gas produced goes up, so pressure goes up. As the bullet moves the volume changes, which changes pressure, which reduces burn rate.

All part of the problems involved in internal ballsitics.

[crackers]

"1 gram of nitrocellulose combusts to @800-1100ccm of gas"

is a statement I found. I would only guess that the product had cooled.

[358429]

There was a Russian handgun that trapped and contained the expanding propellant gases inside of a cylinder inside the cartridge casing.

https://m.youtube.com/watch?v=P_N7AZHpTn4

This is fundamentally different enough theory and operation to be very interesting.[emoji848]


*musing thought(s)*
(I imagine you could reload them with cast hollowpoints and shoot them, safe to plink/shoot indoors into a clay trap without hearing protection.) ( that's what I would want one for) ( maybe if you powder coat the bullets the lead contamination problem no longer is one) ( interesting way to run a recoil operated firearm) (I want to know if it's quieter than my cold steel blow gun[emoji39])

[Alstep]

If I recall correctly, IMR powders all have the same BTU content throughout the whole burn rate range. So I would imagine the gas given off would all be the same volume per pound, no matter what the pressure.

Years ago, I had a discussion with an engineer who was designing an indoor range. The volume of powder gasses was a major consideration in the specs for the ventilating system.