Caution in the cold

[MTLIVIN]

Deleted

 

[johnwm]

My engineering brain has to point out a flaw with the below calculation. I did not look into the Coefficient expansions constants you provide, they are good I'm sure, but I believe your applying them incorrectly. The way you calculated the bore contraction of .00000633*.308*110=.0002144 is not correct, that would be the contraction of a steel bullet or rod .308" in diameter. The bore is air, and the contraction of the steel will occur toward the center of mass of the steel, AKA, it will contract toward the center from both the outside wall and inside wall, or bore (think of a midpoint in the cut section of a barrel, and the steel contracting in all directions toward this point).

Therefore the outside barrel diameter will decrease when cold and the inside bore diameter actually increases when cold. The opposite is true for a hot barrel, the outer barrel diameter will increase and the inside bore dimension will be reduced when hot. So, if you could isolate all other variables (like powder temp burn rates and bullet shrinking or swelling from temperature) you will build more pressure and get higher velocities with a hot barrel vs a cold barrel due to bore diameter.

Id have to pull out my notes from my materials class to give you anymore data, but I believe the concepts I provided above to be accurate.

Based upon this logic, heat-shrink tubing wouldn't shrink when heated; it would stay the same size but the thickness of the walls would decrease.

If you imagine the molecules adjacent to one another on the interior surface of the bore, and then picture them losing energy (cooling) and becoming "smaller" for lack of a better term, there's no way that they will become further apart from one another, which is what they would need to do if your interpretation is correct.

 

[MTLIVIN]

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[johnwm]

The heat-shrink comparison was simplistic, of course. As far as the rest of it, I don't pretend to be a physicist. Perhaps you could explain, in small words of course, how the interior surface of the bore would experience the phenomenon of contracting molecules actually moving further apart. I would bet good money that a metal container whose interior volume could be measure precisely would show a definite increase in internal volume when heated, and a decrease when cooled.

If you say it's not so, that's okay. But I will point out that having someone, PhD or otherwise, attempt to teach you something...does not necessarily guarantee that you learned it. Cheers!

 

[Hand Skills]

I have shot a few rounds in the cold myself.

I'll posit that the extreme pressures some folks have seen has more to do with chemistry than geometry.

Temperature affects the retardants in double based powder. This is known. Get a super slow, double based powder in the cold with low casefill and you are asking for trouble (powder bridging). Stick with single based powders and good casefill (95% or better) and I believe all will be well.

No PhD here, just a few decades of life in Canada.

 

[tankgijohn72]

To be clear copper being slightly harder at colder temperatures is a WAG. I doubt it really has much effect at all. I think its the powder, but my cold chamber in the basement only goes to 0 degrees and is full of venison. So i doubt i will be doing any cold weather testing to confirm the theory.

 

[cohunt]

A hole in steel (a steel ring) gets larger when heated and smaller when cooled unless it is restrained by a not heated material around it. So on a gun barrel that is left in the cold so that the barrel comes to full outside temp, the bore diameter is smaller in the cold.

Comparison: when a bearing race is pressed over a solid shaft, if you heat only the race and not the shaft, it will expand and fall off

 

[MTLIVIN]

COHUNT your correct, I did some more research and was off on my statement.

 

[johnwm]

 

[Cold Trigger Finger]

I find it kind of funny when I read something about hunting in cold weather and find out half way through they are talking about above 0.

I'm NOT talking about ball cap weather as being cold.

 

[skipglo]

At the risk of starting something.
But because I've experienced the results I will share this.
With this batch of cold temps in the lower 48. Some may want to brave the cold and see how their rifles and other firearms handle the cold. True , Cold . 40 below ambient type temps.
Rifle barrels, being made from round , steel alloy . they contract in the cold. The colder it gets , the more they contract.
That contraction / making the interior dimensions smaller. Jacks the pressure WAY UP.
I imagine most long range hunters and shooters use temp stable powder and often magnum primers to get good ignition and lower SD.
Which can spell disaster when a load that produces full SAAMI spec pressures with normal ambient dimension s . Is fired in a much smaller chamber and barrel.
Anyway.
I just hope everyone is cautious.

Interesting thought and should in theory be true. However...to help dispell the myth... I live in Northern Alberta Canada and I'm sure some folks from Alaska and Siberia can jump in here...40 degrees below ambient lower 48 is what? 0-20 farenheight. For 45 years I have hunted in-25 to -30 farenheight and have never popped a primer or had a casing stick. The only thing that stuck once or twice was my sweaty hand on the receiver after pulling it out of a mitten with a Hot Shot in it.

 

[Cold Trigger Finger]

Interesting thought and should in theory be true. However...to help dispell the myth... I live in Northern Alberta Canada and I'm sure some folks from Alaska and Siberia can jump in here...40 degrees below ambient lower 48 is what? 0-20 farenheight. For 45 years I have hunted in-25 to -30 farenheight and have never popped a primer or had a casing stick. The only thing that stuck once or twice was my sweaty hand on the receiver after pulling it out of a mitten with a Hot Shot in it.

Ambient being the air temperature. Not windchill temp.
I live @ 62+ ° N. Lat.
If you tap my user name the page will come up that says where I live.
And no its not a myth. I've done lots of shooting @ -40° ambient and colder.

 

[skipglo]

Ambient being the air temperature. Not windchill temp.
I live @ 62+ ° N. Lat.
If you tap my user name the page will come up that says where I live.
And no its not a myth. I've done lots of shooting @ -40° ambient and colder.[/QUOTE

 

[skipglo]

Fairly new so thanks for the tip on finding folks location. So what were the failures you experienced if you don't mind telling me and what powder. I will be sure not to use it!