Why does muzzle velocity increase with barrel heat

[Okie4570]

For the ID to decrease in size, then molecules lining the innermost aspect of the barrel would have to collapse against themselves. When heated, the exact opposite is what occurs. Those molecules expand, thus increasing the diameter of the bore.

Pretty sure I just learned something today. Now I've got to go get the 30-378wby out, 10 rounds of ammo, micrometer, and finish convincing myself, lol

N2Sooners, I could have used that bearing heater on a few farm implements, had no idea such a thing existed. Our heater was a torch!

 

[CHenry]

For the ID to decrease in size, then molecules lining the innermost aspect of the barrel would have to collapse against themselves. When heated, the exact opposite is what occurs. Those molecules expand, thus increasing the diameter of the bore.

That does make sense.
so back to the original question...

 

[KOPBET]

maybe you should ask Jason Collins?

 

[dennishoddy]

When we remove large bearing races here at the plant, the inner race, and balls are typically destroyed, leaving the outer race. A welder will run a bead around the inside of the outer race, and the bearing race will just fall out.
When a new bearing is installed on a shaft, the bearing is put on a cone shaped heater that will expand the inner race, and allow the bearing to be dropped onto the shaft instead of having to be pressed in.
If a sleeve bearing is to be installed, its typically several thousanths of an inch oversize for the hole its to be put in. We put the sleeve in liquid nitrogen and basically drop it into the hole, boring out the ID to fit the shaft going through it when the temperature returns to ambient.

 

[druryj]

So for the bingo guy and the increased pressure dude...why did the pressure increase?

Charles's law
(also known as the law of volumes) is an experimental gas law which describes how gases tend to expand when heated. A modern statement of Charles's law is:
The volume of a given mass of an ideal gas is directly proportional to its temperature on the absolute temperature scale (in Kelvins) if pressure and the amount of gas remain constant; that is, the volume of the gas increases or decreases by the same factor as its temperature

(Ergo; Bingo).

 

[Okie4570]

Charles Law works with solids and liquids? Pressure on a solid and liquid responds to pressure changes like a gas does?

 

[druryj]

Charles Law works with solids and liquids? Pressure on a solid and liquid responds to pressure changes like a gas does?

The application of Charles law here makes perfect sense to me: The question is: "Why does muzzle velocity increase with barrel heat" What we have is an instance where volume is a relative constant, and heat is increased rather quickly within that somewhat constrained volume, caused by the rapidly burning gases following ignition of the powder within that constrained volume; resulting in an increase in the only variable left: Velocity. Think of it like this: A scuba tank is filled to a certain pressure, measured in psi, and is left to sit in the heat of the sun, what is the variable that increases? Pressure (Within the constrained volume of the tank).

Make sense?

There's not any liquid involved in this instance but if you will study the effects of pressure or heat on liquids, it is indeed much different.

 

[dennishoddy]

The application of Charles law here makes perfect sense to me: The question is: "Why does muzzle velocity increase with barrel heat" What we have is an instance where volume is a relative constant, and heat is increased rather quickly within that somewhat constrained volume, caused by the rapidly burning gases following ignition of the powder within that constrained volume; resulting in an increase in the only variable left: Velocity. Think of it like this: A scuba tank is filled to a certain pressure, measured in psi, and is left to sit in the heat of the sun, what is the variable that increases? Pressure (Within the constrained volume of the tank).

Make sense?

There's not any liquid involved in this instance but if you will study the effects of pressure or heat on liquids, it is indeed much different.

Ok, The gas bottle case is relevant. I deal with that every day when I have to measure the test gas in our CEM system.
It has nothing to do with what happens in the chamber/barrel of a gun.
Barrel heat is caused by friction, and the temperature of the propellant.
I would have to equate the "Charles's law
(also known as the law of volumes) is an experimental gas law: as a means to measure the temperature of the gas, but then we have the structure of the steel. Different alloys have different properties. For example: 1018 cold rolled vs Inconel, vs 4140 which lots of gun barrels are made from. Military grade barrels are made from 41V50 milspec vanadium/molybdenum alloy steel.
Each has their own property's when heat treated, and subjected to sustained fire.

As an example at our plant, we have to remove ring gears that weigh around a ton from a shaft. It takes 4 guys with rose bud torches to start from the outside of the gear and work their way into the center. After the outside steel expands, it gives the inside steel room to move out. As they work toward the center, the gear drops from the shaft.

As posted before, when a pressed in bearing fails, some of which may have 20 pound rollers, welders run a bead around the inner part of the outer race, and it just drops out on the floor.

So, for the record, steel can me made to run either direction depending on where the heat is applied.

 

[doctorjj]

Running a bead on the inner race isn't applying heat to make that inner bearing race shrink. It's about using the property that welds shrink as they cool to draw the race down smaller so that it will come free. So, it's the same principle, but they are applying the steel at the melting temperature and then allowing it to cool and therefore decreasing the diameter. It would be the same principle as applying heat to the hub around the race, or applying cold to the race. It's not that more heat on the inside makes the inside shrink. So the steel doesn't run in any direction depending on where the heat is applied. Heat is applied, steel expands. Period.

 

[davek]

Time to contact MythBusters.