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Old February 29, 2008, 05:39 AM   #1
300WM Andy
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Join Date: February 29, 2008
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Any ideas on pressure signs an cold weather?

Couple of years ago over in the South Island NewZealand it snowed when we were a long way from the chopper and civilisation. ( Tahr hunting)

While there were some uncomfortable moments with the temperatures we had all rifles that had previously shown no sign of pressures give some surprising results - excessive pressure signs.

EG:
A 300 WM (with 3 grains over max ) suddenly had trouble opening the bolt and hey the primer popped out.
A 300 RUM just less than maximum was a wee bit sticky to open and the micrometer showed greater than acceptable expansion.
A 30-06 was similar.
Obviously exceeding the published data is risky but the loader had worked up this load gradually and no signs were forthcomming - until this cold trip.

We do not normally experience these issues and were surprised as most literature suggest that pressure signs should occur in HOT temperature not cold temperatures.

Any ideas from an Alaskan ?

Rifles and ammo would have been at ambient temperature as were left upright outside the tent in 5 inches of dry snow. Probably -10 degrees.

Altitude would be approx 500 m above sea level.

Could it be the throat contracted in the cold ( does it happen this way? ie an opening get smaller in cold metal? )
Could the temperature slowed the ignition so jump may have been a bit slow?

Any ideas...it was cold enough to make a brass monkey worried!!!
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Old February 29, 2008, 10:14 AM   #2
SL1
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Did you look down the bores in the morning?

Andy,

You wrote:

"Rifles and ammo would have been at ambient temperature as were left upright outside the tent in 5 inches of dry snow. Probably -10 degrees."

One thought came to mind as I read that: Are you sure that no moisture got into your barrels and froze to your bores overnight? Even a sprinkle of snow or frost in the bores might substantially increase pressures in already hot loads.

SL1
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Old February 29, 2008, 02:07 PM   #3
ClarkEMyers
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See Bob Hagel's guns and loads books for some thoughts.

See Bob Hagel's guns and loads books for some thoughts. He loaded above current book figures for most of his own firearms and was well placed to do cold soak tests and write about them - which he did.

I have no idea whether the temperature reference is Celsius of Fahrenheit but in either case it does not strike me as terribly cold. On my own experience I'd expect trouble with only a few powders - and nothing in those calibers - Blue Dot is notoriously cold sensative.

There was a time and it may still be true that all Norma sporting powders were qualified just the same as their military jet aircraft powders - normal performance to -40 (either system)
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Old March 7, 2008, 05:40 PM   #4
300WM Andy
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Sorry for the delay I have just joined up and having some delays navigating around - all ok now...

Yes you would be right - from your perspective it wasn't that cold for North American conditions. Yes I need to state the unit of temperature - the temperature was around -10 degree Celsius or 14 degree Fahrenheit for overnight minimum. Probably 3-4 degrees Celsius or 276 degrees Fahrenheit.

While we ( in Australia) think that temperature is cold I wanted to put this post on this site as the extreme low temperatures you experience in North America may mean there is more general knowledge going around.

All rifles had muzzles taped up - but moisture could have been present I guess from condensation. However this is unlikely.

We had sighted in rifles so no oil should have been present. We also had all fired at game several days earlier in the trip without any pressure issues.

As for powders - loads used Mulwex AR 2209 ( an Australian powder) and Winchester WXR powder.

One theory put to me was that throat may have contracted in the cold. However, the lead/copper coefficient of the bullet is such that any contraction should have been more. However this is where I was at.

Thanks for the ideas so far..... any body out there hunt in the cold that has experienced any similar issues?

Cheers

Andy
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Old March 7, 2008, 06:57 PM   #5
Tom Matiska
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Any chance you are being too generous with the last oily patch after cleaning??? What type of oil?

Most misfire stories I'm familiar with start with somebody who uses too heavy of a lube(or some off brand 3 in 1 oil with too much parafin) and ends when their firing pin being sticky on a cold morning hunt.

Winchester Ball Powder manual had a long history of some pretty tame data (that few liked to use), but they did the muzzle up/down, 140F/-40F etc.... testing and their data set the gold standard for safety. ...... left me to wonder what extremes were being tested (or not?) by those publishing hotter data.


edit..... oops my bad... missed the 4th post where you said you fired them since cleaning.....

Last edited by Tom Matiska; March 8, 2008 at 01:36 AM. Reason: I goofed
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