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#66028 11/12/07 03:57 PM
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Why do shotshells seem to under-perform on a cold day vs. warm day?
John


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Shotshell performance is based on powder burn. Chemical reactions are highly dependent on temperature. Propellants, such as nitro powder, are also dependent on pressure for burn rate. The initial cold temperature must be overcome to raise the temperature and pressure sufficintly to achieve normal burn rate. That itty bitty fraction of a second while the powder jump starts itself can sometimes be sensed. A blooper occurs when the powder can't develop enough pressure to get up to normal burn rate before the shot charge moves and increases the combustion chamber volume.

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They don't just "Seem To" they actually do. This has been well documented under lab conditions. The Cold Powder doesn't build pressure as fast. Some powders can build excessive pressure under extreme hot conditions. Also some powders are more sensitive to temp changes than others. A fast powder is apt to be more sensitive to "Hot" & a slow powder to "Cold". A slow powder loaded to borderline pressures for it's design characteristics can give total failure in the very cold.


Miller/TN
I Didn't Say Everything I Said, Yogi Berra
2-piper #66045 11/12/07 05:36 PM
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Smile if you like, but for cold weather I use 700X at low pressure, no 4756 or 7625 for me.

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Rocketman, as usual, offers a superb explanation.
I use ADI (Australian Defence Industries) powders (many of which are packaged and sold as Hodgdon in the US - for cheaper than we pay here!); temperature sensitivity is something they pride themselves on minimising, borne of research into propellants for military applications under extreme climate variations.
RG.

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Balistic Products had cautioned me about the following load that they provided the recipe for.....that it would not do very well in cold weather:

12 ga. 2-3/4 WAA hull
W209 primer
W540 - 34.1 gr.
Balistic Prod. BP12/BPGS + 20 ga. felt in bottom of plastic wad
1-1/4 oz. #5 nickel-plate shot
Tyvek over-card
8-star crimp

Yes, the colder it gets, the less bang (sound) that I get out of it.
John


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Another factor in degraded cold weather performance may be the wad becoming stiffer, less flexible and not sealing the load as well.

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Keith, you are right. Our club sold really cheap 12 ga wads years ago, and in our Manitoba winters, at -10oC or less these wads turned brittle and seemed to shatter when fired as opposed to Federal and Winchester wads on the same day. Bloopers indeed.
Mike

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Question: what is the "standard" temperature that shells are pressure tested?


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Quote:
Smile if you like, but for cold weather I use 700X at low pressure, no 4756 or 7625 for me.

No smiles from me King; I swore off 7625 about 30yrs ago. Was using a load straight from the then DuPont manual in 12ga with 1¼oz shot @ about 7K psi. We were breaking ice to get a john boat back in the woods in a duck swamp & it totally let me down. I mostly use Green Dot now.


Miller/TN
I Didn't Say Everything I Said, Yogi Berra
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