Why does muzzle velocity increase with barrel heat

[dennishoddy]

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.

I'm talking about welding the inside of an outer race, not running a bead on the inner race that you said. That won't work.

When we take the one ton gear off the shaft, one crew started heating the gear from the inside, before heating the outside. The gear galded to the shaft as it had nowhere to go but in vs out if one starts heating from the outside to the inside. The steel had nowhere to go but IN.

 

[doctorjj]

I'm talking about welding the inside of an outer race, not running a bead on the inner race that you said. That won't work.

When we take the one ton gear off the shaft, one crew started heating the gear from the inside, before heating the outside. The gear galded to the shaft as it had nowhere to go but in vs out if one starts heating from the outside to the inside. The steel had nowhere to go but IN.

I know what you're talking about. (Posting from my phone so inner vs inside was a typo). Welding to the inside of the outer race to get the outer race to drop out. It's not applying heat to the inside of the outer race that makes it become smaller. It's the weld shrinking as it cools that draws that race down and let's it fall free. Otherwise you could just use a torch to heat the race and it would fall free I can tell you that absolutely won't work. The welding technique works, not because you are applying heat to the race. It works because as the new weld cools, it shrinks. So it's still heat=expansion and cool=contraction.

And you can heat the part you're trying to make bigger from anywhere you want. Inside, outside doesn't matter. It's always gonna get bigger as it gets hotter.

 

[druryj]

Time to contact MythBusters.

This! LOL!

 

[Toney]

I think the metal will expand in all directions. The barrel would get thicker, but it would also grow bigger around so.....

 

[Yourshoesareuntied]

I appreciate the interest and thought put into the post.

 

[BrandonM]

While we're at it. Where do babies come from?

 

[Yourshoesareuntied]

While we're at it. Where do babies come from?

I know the answer to that one, was working on putting one together this morning

 

[7stw]

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.

Never shot full auto enough but shooting prarie dogs with a bolt gun and using ball powder and rounds sitting in the sun and a hot barrel yes I have experienced a cook off and it will scare the $h!t out of a person and those around you. I've since learned that lesson and now keep ammo in the shade and fire shorter shot strings from each rifle while decimating prarie poodles. I have learned that the chambers most often contract but will expand when shooting. I most often experience contraction as noticed by tougher extraction after shooting in a warm to hot barrel. And increased signs of case head separation in hotter higher velocity rounds.

 

[SoonerP226]

Interestingly (or not), the idiots on Car Talk covered a topic strikingly similar to this in last week's show. Take a listen to Segment 5 (Does being a shade tree mechanic violate the Laws of Physics?) here: http://www.cartalk.com/content/1318-great-lion-escape

 

[doctorjj]

The guys on Car Talk are wrong. The guy who called in remembered the experiment backwards. The ball won't fit through the ring until you heat the ring.

http://m.youtube.com/#/watch?v=ZunJ7oHuttQ&desktop_uri=/watch?v=ZunJ7oHuttQ

http://m.youtube.com/#/watch?v=wFIgskt1Yek&desktop_uri=/watch?v=wFIgskt1Yek