Why does muzzle velocity increase with barrel heat

[Yourshoesareuntied]

Why does muzzle velocity increase with barrel heat?

 

[CHenry]

Increased pressure.

 

[druryj]

Increased pressure.

Bingo! We have a winner.

 

[Okie4570]

As the barrel heats, it expands, making the bore smaller in diameter than a cool one, therefore increasing the pressure behind the bullet to push it out, as stated above.

 

[oneof79]

I always thought that a hot barrel heated the cartridge up causing more velocity.

 

[Yourshoesareuntied]

I understand increased pressure "normally" means increased muzzle velocity, but it seems that a hot barrel means the bore is slightly larger or expanded, and that makes me think the bullet will slip through the barrel with less friction therefore reducing pressure and muzzle velocity.

 

[Yourshoesareuntied]

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

 

[Toney]

Chemical reactions are faster when hotter

 

[dennishoddy]

Lol. In a semi auto, or a full auto, the rounds are ambient temp if fired rapidly. When I was shooting the M60, and it was hot, a cook-off was pretty common.
I doubt most on here have put that many rounds through a barrel.
Like has been said, the barrel expands in two directions. Inward and outward. Its not much, but it will make a difference.

 

[uncle money bags]

Lol. In a semi auto, or a full auto, the rounds are ambient temp if fired rapidly. When I was shooting the M60, and it was hot, a cook-off was pretty common.
I doubt most on here have put that many rounds through a barrel.
Like has been said, the barrel expands in two directions. Inward and outward. Its not much, but it will make a difference.

Oh dude, now i really miss my pig. Well, Uncle Sams pig which was lent to me for several glorious years.