Pressure at low temp???

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nof60

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Has anyone experienced a pressure spike due to low temp?

I have used the same load (admitedly it is pretty hot and a bit above max) but have never had excessive pressure from it. The other day rifle was cold cold (-35) and when I took a shot through it to check alignment while hunting the case would not extract, had to use the truck antenna to pop case out of chamber but while doing this dropped it in deep snow and could not find case to examine. Was shooting over the hood of the truck and it blew a bunch of snow ice off hood to the side so wondering if case seperated a bit?

My thoughts are that the barrel contracted enough at the extreme low temp to cause a pressure spike. Bullet hit target dead on. Tried a second shot and did not repeat results. Tried a shot yesterday amd it did not repeat but rifle and ammo was warm.
 
Was the cartridge cold or was it still warm from the cab of the truck?

My guess would be a little extra powder ended up in that case.
Possibly a bit of faster powder from a previous loading session was left in your thrower and it ended up in that case?
 
coyoteking said:
Was the cartridge cold or was it still warm from the cab of the truck?

My guess would be a little extra powder ended up in that case.
Possibly a bit of faster powder from a previous loading session was left in your thrower and it ended up in that case?
Click to expand...

Cartridge was also cold but maybe slightly warmer than rifle. No possibilty of extra powder or wrong powder. Powder is weighed individually, i also weigh the loaded cartridge to double check.
 
Is it possible at that temperature the case contracted some along with the chamber and possibly even more neck tension could add up to put a max load over the edge?
 
nof60 said:
Cartridge was also cold but maybe slightly warmer than rifle. No possibilty of extra powder or wrong powder. Powder is weighed individually, i also weigh the loaded cartridge to double check.
Click to expand...

Yeah, I’m hyper vigilant in my process like you.

Ganderite and Bigedp will be along shortly with your answer.
 
Rifle is a .300 WBY Mk V Accumark. I have had it many years since new and shot at least a couple hundred rounds through it

Load is
.300 WBY
Fed Mag primers
80.5 gr Hybrid 100V (2.5 gr over max load in nosler book)
180 gr CT Ballistic Silvertip

I have used this recipe for at least 5 years and have shot at least 100 of these. I will weigh some older ones against a new batch I loaded a month ago in the morning to rule out powder error but I am very precise so really do not think it was a reloading error.
 
Possibly your OAL could have been off? Was it now starting touching the rifling on that particular round? Might just be one that wasn’t seated deep enough.

Your barrel would have contracted approximately .00077” based off a standard room temp to -35 degrees C. The bullet if it was pure copper would be about .0009” contraction, I am not sure about leads contraction rate. I suspect the bullet if the same temp as the gun would be smaller in diameter not larger.
 
Standardvel said:
Is it possible at that temperature the case contracted some along with the chamber and possibly even more neck tension could add up to put a max load over the edge?
Click to expand...

My working theory is that at the cold temp (rifle was in truck overnight and in the backseat in a case under some coats during day) that the chamber and barrel contracted putting an already hot load over the top. Main reason I am concerned is that a stuck case would suck if a follow up shot was needed on an animal. Not terrible concerned about the action letting go. I might have to cook up a lower load for extreme cold hunting and then would have to track scope setting etc etc for this in the future. Might end up taking my .375 for the rest of the hunt but it has no glass and I would prefer a scope for elk.
 
Eaglelord17 said:
Possibly your OAL could have been off? Was it now starting touching the rifling on that particular round? Might just be one that wasn’t seated deep enough.

Your barrel would have contracted approximately .00077” based off a standard room temp to -35 degrees C. The bullet if it was pure copper would be about .0009” contraction, I am not sure about leads contraction rate. I suspect the bullet if the same temp as the gun would be smaller in diameter not larger.
Click to expand...

Did not feel like it and for this rifle they do jump a bit to the lands. Although the action was a bit stiff as you can imagine.
 
From all I ever heard is pressure dropped at lower temps... it will be interesting to know about your finds if you do find out!!
 
Secondary pressure spike brought on by poor cold weather ignition with a temperature sensitive powder. Pressure drops after shot start, bullet slows (or even stops) then powder charge finally decides to really light up and catches up to the bullet.

A hang-fire is a click-bang. This is more like a click-bang-sizzle-BOOM.
 
Not in brass, face-centered cubic crystal structures are virtually unaffected by temperatures down to at least liquid CO2 numbers, and generally much lower.

Probably not in the steel, either. Impact toughness is the only property dramatically affected by the cold, and it's hard to see how that could cause a pressure event in a rifle. Ductile-to-brittle transition temps have improved a lot since the refining advances that came out of WWII, so even that isn't the problem it was, say back in the days of the Titanic.
 
Dogleg said:
Secondary pressure spike brought on by poor cold weather ignition with a temperature sensitive powder. Pressure drops after shot start, bullet slows (or even stops) then powder charge finally decides to really light up and catches up to the bullet.

A hang-fire is a click-bang. This is more like a click-bang-sizzle-BOOM.
Click to expand...

This is my guess as well. Got a partial ignite, then delay while pressure accumulated and then it all went off. If it happens again I would see if I could find extra hot primers. Thermal contraction over the diameter of a barrel or case would not be enough to make such a difference.
 
So it was not as cold today but did an experiment. Left rifle and ammo outside about -27. Shot a shot. Not pressure like yesterday but bolt handle felt a bit stiffer than normal to lift but could just have been from cold. Brass did not show excessive pressure signs. Brought rifle and ammo inside for a few hours till room temp. Shot it. Bolt handle easy to lift. I need to run 2 more checks with warm ammo and cold rifle and vice versa.

Nothing I have read says hybrid 100v is terribly temp sensitive. At this point I am thinking it is one of 5 things. 1)Barrel contracting in cold (although I am having a hard time believing this), 2)Lubalox???coating on the CT bullets responds poorly to extreme cold, 3)click-bang-sizzle-boom (possible but I have never had that problem with these primers although I usually only hunt with Retumbo at these temps as I am usually after bison with a .375) 4) a bad one slipped through the reloading process 5) Case seperated. I wish I had not dropped it. Tempted to go back with a metal detector

I went back and reweighed all the cartridges loaded as well as some older ones that are the same loading and they are all the same so if it was a reloading error it was a one off.
 
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