Caution in the cold

[Litehiker]

Interesting discussion. Here's an interesting one for you.

When I was a Nordic Ski Patroller in the 1979 Pre-Olympics (and later the '80 Olympics) at Lake Placid, NY I patrolled the Biathalon events. I heard that only the Austrian and Russian rifles would shoot well in sub-zero temps and the morning began at -20 F.
So we waited three hours until the temps got to -10 F. when it was deemed safe to ski.

What did the Austrians know and the Russians discover from them about shooting .22 LR in sub zero temps? The Austrians discovered they needed a "swamped" barrel whose bore gradually tapered toward the muzzle a few thousands smaller than SAAMI specs.

THAT was the "secret sauce" for .22 LR accuracy in extreme cold. HA!
Too bad poor Remington didn't know that. They tried and finally gave up on building a good biathlon rifle for the American team.

BTW, the last day of the Pre-Olympics was -40 F. at Lake Placid and -50 down in Keene Valley! All Nordic events were cancelled - after we Patrollers spent over an hour out on the trains in position for first aid evacuation with our specialized toboggans.

Eric B.

 

[David Urasky]

I find this idea interesting so I did some digging in my Machinery's Handbook (the machinist's bible) and applied some laws of Physics.

Coefficients of thermal expansion is how much the material will expand or contract with temperature change. It's measured in units of linear expansion per unit of length per Deg. F.

Carbon Steel 0.00000633"/1" length/degree F

Before you get all crazy about your barrel material carbon steel is mostly iron, about 98-99% iron. 4100 series steels (chrome moly) is about 98% iron. 400 series stainless is about 85% iron. So they are all pretty similar for iron content. Since I don't have thermal expansion rates handy for all alloy types iron will have to do.

So your barrel has an average diameter of 1" for ease of numbers and you're shooting a 308. So the outside of the barrel will contract 0.00000633*1" diameter of barrel*(+80 deg to -30= 110 change) = .0006963". But the outside of the barrel means nothing to the bullet. The bore, which contacts the bullet, would contract .00000633*.308*110=.0002144" Now let's remember that.

The bullet, mostly lead with a thin jacket which is made to deform, has a coefficient of thermal expansion of 0.0000163. So your bullet will contract .0000163*.308*110=.00068134"

So, your barrel shrinks .0002144" while the bullet shrinks .00068134" meaning your bullet shrinks .000466" more than the barrel. So it's looser in the barrel!!! Should be lower pressures for the first round. After that, your barrel temperature has risen from each previous shot meaning it gets bigger but the bullet is still the same size … unless you leave it in a warm chamber and it has the chance to heat up. And, as the bullet travels down the barrel it heats from hot gasses behind it and friction consequently it gets bigger the further it goes down the barrel which happens no matter what the temperature is. So the bullet is tighter in the barrel the further down the barrel because the bullet is heating but the barrel is still cold in front of the bullet.

So based on all of that mess, I don't think any of that's worth understanding. But I found it sort of fun. I believe it comes down to powder temperature. Which is why in 1000 yard F class competition we will place the cartridge into the action, but not close the bolt until you've figured your hold from the previous shot. Then close the bolt that put the cartridge into a hot chamber and shoot. Don't ***** foot around and let the powder heat up or burn rate WILL change as will point of impact. And when trying to hit a 5" X ring at 1000 yards you need to be consistent.

Since I've seen point of impact change because of powder temperature increasing, it stands to reason that it will also change when the temperature drops. Which is why I have different loads, in fact different powder, for my 20 Tactical for shooting coyotes in the winter and P-dogs in the summer. Coyotes one shot, one kill, cold barrel, cold ammo. P-dogs 80+ degrees hot sun, hot ammo and way hot barrel from multiple shots.

Now wasn't that fun?

 

[ajkellerusmc]

I live in AZ and I had some 338 Lapua hand loads, 1 grain below maximum with Retumbo that I shot at 7500 ft elevation in 70 degree conditions last summer that were normal with easy bolt lift and no flat primers or ejector marks on the case heads.

I then tried to shoot the same loads in phoenix at 110 degrees and had stuck cases and torn off case rims by the extractor. I shot 2 rounds and stopped! Is the problem about pressure with heat or cold or both? And which is Worse?

 

[tankgijohn72]

Depends on the set of conditions and components. Some powders get a little faster MV when colder, some get slower. Some rifle bores are looser than others, some rougher etc. Generally speaking pressure gets higher when hotter, but not always the case.

I live in AZ and I had some 338 Lapua hand loads, 1 grain below maximum with Retumbo that I shot at 7500 ft elevation in 70 degree conditions last summer that were normal with easy bolt lift and no flat primers or ejector marks on the case heads.

I then tried to shoot the same loads in phoenix at 110 degrees and had stuck cases and torn off case rims by the extractor. I shot 2 rounds and stopped! Is the problem about pressure with heat or cold or both? And which is Worse?

 

[ncmeatgrinder]

I wonder what the Russian snipers of WW II would think of this thread? I do not believe the cold hindered there ability to shoot.

 

[astronut502]

"Cold Trigger Finger, post: 1563900, member: 56732"]At the risk of starting something.
But because I've experienced the results I will share this............................... "

Cold Trigger Finger, this is an interesting premise. I am a chemist, so I ran the numbers to see just what change in volume and thus pressure should be expected by a significant drop in temperature, and thus volume, in the chamber. Lets assume a few things:

1: The chamber is 1/2" x 3" in size at +40F. (a bit larger than a .338 Lapua Magnum cartridge]
2: The temperature drop is from +40F to -20F. [Burrr]
3: The chamber is made from carbon steel.

The thermal coefficient of expansion for carbon steel is 11.0x10e-6 to 12.5x10e-6 u/u degree C. [This value is available at many places on the internet] Lets use 12.0x10e-6.

The volume for the chamber calculates to 0.589 cubic inches [cuin] at +40F.

If the change in temperature is a differential of 60F (+40 to -20) [33.3C], then change in the chamber volume is a decrease of 0.000000000012 cuin (1.2x10e-11 cuin). So, the 'cold' chamber volume at -20F is 0.588999999988 cuin.

Stay with me.

The Ideal Gas Law is PV=nRT. It governs how a gas at varying volumes will change in presssure. Without getting too messy here, n is the number of molecules of gas in the container, R is the gas constant, T is the temperature in degerees Kelvin, V is the volume of the container and P is the pressure. So, we can say that PV/nRT = P'V'/nRT', where the prime(') values represent the chamber at the lower ambient temperature. Since the number of molecules of gas (exploding powder) are the same in each instance, n cancels out of the equation. The R value is a constant, so it cancels out, also. T should be the same in each equation since the amount of heat being generated by the chemical reaction of the exploding gas should be the same, so it cancels out, too. (One could argue that, at the lower temp, the reaction would proceed more slowly, thus the heat has more chance to transfer off into the chamber wall, but that would also lower the pressure. This is one of the reasons we see lower muzzle velocities at lower powder temperatures)

That leaves us with PV=P'V' [Boyle's Gas Law]

[I'm going to use non-standard units for this calculation for simplicity, but the answer still works out becaue the units are consistent]

Lets assume that +40F chamber pressure of our round is 60,000 psi. We already know that the volume is 0.589 cuin.

So: PV=P'V'
60,000 psi * 0.598 cuin = P' * 0.588999999988 cuin
This rearanges to:
P' = (60,000 psi * 0.598 cuin)/0.588999999988 cuin
Solve for p:
P' = 60008 psi when the temerature of the chamber is -20F.

If there are holes in this calculation, please let me know. ;-)

I wonder if there is more danger of the barrel/receiver steel becoming brittle at lower temperatures. Some of the mild carbon steels drop off rapidly in impact resistance at temperatures below zero centigrade.

For what it's worth..........

 

[Canhunter35]

I wonder what the Russian snipers of WW II would think of this thread? I do not believe the cold hindered there ability to shoot.

especially that Finnish guy they called white death. He would lay for hours under the snow waiting to make his shot

 

[tankgijohn72]

Never thought i would see pivnert (PV=nRT) on this forum. Based off of your calcs, think anyone can "see" an 8 psi increase in their brass? No way. Change in burn rate of powder and primer ignition have to be main variables. One may be able to argue a change in bore condition after a few rapid shots that causes water to condense in bore then freeze and increase pressure. Either way I'm not worried about shooting when its cold out.

"Cold Trigger Finger, post: 1563900, member: 56732"]At the risk of starting something.
But because I've experienced the results I will share this............................... "

Cold Trigger Finger, this is an interesting premise. I am a chemist, so I ran the numbers to see just what change in volume and thus pressure should be expected by a significant drop in temperature, and thus volume, in the chamber. Lets assume a few things:

1: The chamber is 1/2" x 3" in size at +40F. (a bit larger than a .338 Lapua Magnum cartridge]
2: The temperature drop is from +40F to -20F. [Burrr]
3: The chamber is made from carbon steel.

The thermal coefficient of expansion for carbon steel is 11.0x10e-6 to 12.5x10e-6 u/u degree C. [This value is available at many places on the internet] Lets use 12.0x10e-6.

The volume for the chamber calculates to 0.589 cubic inches [cuin] at +40F.

If the change in temperature is a differential of 60F (+40 to -20) [33.3C], then change in the chamber volume is a decrease of 0.000000000012 cuin (1.2x10e-11 cuin). So, the 'cold' chamber volume at -20F is 0.588999999988 cuin.

Stay with me.

The Ideal Gas Law is PV=nRT. It governs how a gas at varying volumes will change in presssure. Without getting too messy here, n is the number of molecules of gas in the container, R is the gas constant, T is the temperature in degerees Kelvin, V is the volume of the container and P is the pressure. So, we can say that PV/nRT = P'V'/nRT', where the prime(') values represent the chamber at the lower ambient temperature. Since the number of molecules of gas (exploding powder) are the same in each instance, n cancels out of the equation. The R value is a constant, so it cancels out, also. T should be the same in each equation since the amount of heat being generated by the chemical reaction of the exploding gas should be the same, so it cancels out, too. (One could argue that, at the lower temp, the reaction would proceed more slowly, thus the heat has more chance to transfer off into the chamber wall, but that would also lower the pressure. This is one of the reasons we see lower muzzle velocities at lower powder temperatures)

That leaves us with PV=P'V' [Boyle's Gas Law]

[I'm going to use non-standard units for this calculation for simplicity, but the answer still works out becaue the units are consistent]

Lets assume that +40F chamber pressure of our round is 60,000 psi. We already know that the volume is 0.589 cuin.

So: PV=P'V'
60,000 psi * 0.598 cuin = P' * 0.588999999988 cuin
This rearanges to:
P' = (60,000 psi * 0.598 cuin)/0.588999999988 cuin
Solve for p:
P' = 60008 psi when the temerature of the chamber is -20F.

If there are holes in this calculation, please let me know. ;-)

I wonder if there is more danger of the barrel/receiver steel becoming brittle at lower temperatures. Some of the mild carbon steels drop off rapidly in impact resistance at temperatures below zero centigrade.

For what it's worth..........

"Cold Trigger Finger, post: 1563900, member: 56732"]At the risk of starting something.
But because I've experienced the results I will share this............................... "

Cold Trigger Finger, this is an interesting premise. I am a chemist, so I ran the numbers to see just what change in volume and thus pressure should be expected by a significant drop in temperature, and thus volume, in the chamber. Lets assume a few things:

1: The chamber is 1/2" x 3" in size at +40F. (a bit larger than a .338 Lapua Magnum cartridge]
2: The temperature drop is from +40F to -20F. [Burrr]
3: The chamber is made from carbon steel.

The thermal coefficient of expansion for carbon steel is 11.0x10e-6 to 12.5x10e-6 u/u degree C. [This value is available at many places on the internet] Lets use 12.0x10e-6.

The volume for the chamber calculates to 0.589 cubic inches [cuin] at +40F.

If the change in temperature is a differential of 60F (+40 to -20) [33.3C], then change in the chamber volume is a decrease of 0.000000000012 cuin (1.2x10e-11 cuin). So, the 'cold' chamber volume at -20F is 0.588999999988 cuin.

Stay with me.

The Ideal Gas Law is PV=nRT. It governs how a gas at varying volumes will change in presssure. Without getting too messy here, n is the number of molecules of gas in the container, R is the gas constant, T is the temperature in degerees Kelvin, V is the volume of the container and P is the pressure. So, we can say that PV/nRT = P'V'/nRT', where the prime(') values represent the chamber at the lower ambient temperature. Since the number of molecules of gas (exploding powder) are the same in each instance, n cancels out of the equation. The R value is a constant, so it cancels out, also. T should be the same in each equation since the amount of heat being generated by the chemical reaction of the exploding gas should be the same, so it cancels out, too. (One could argue that, at the lower temp, the reaction would proceed more slowly, thus the heat has more chance to transfer off into the chamber wall, but that would also lower the pressure. This is one of the reasons we see lower muzzle velocities at lower powder temperatures)

That leaves us with PV=P'V' [Boyle's Gas Law]

[I'm going to use non-standard units for this calculation for simplicity, but the answer still works out becaue the units are consistent]

Lets assume that +40F chamber pressure of our round is 60,000 psi. We already know that the volume is 0.589 cuin.

So: PV=P'V'
60,000 psi * 0.598 cuin = P' * 0.588999999988 cuin
This rearanges to:
P' = (60,000 psi * 0.598 cuin)/0.588999999988 cuin
Solve for p:
P' = 60008 psi when the temerature of the chamber is -20F.

If there are holes in this calculation, please let me know. ;-)

I wonder if there is more danger of the barrel/receiver steel becoming brittle at lower temperatures. Some of the mild carbon steels drop off rapidly in impact resistance at temperatures below zero centigrade.

For what it's worth..........

 

[Cold Trigger Finger]

So your brass case would contract to?

No, brass doesn't contract the same as steel.

 

[Cold Trigger Finger]

Not saying it can't happen but I have coyote hunted with 223 and 6mm Ai in -30s and never seen anything. It wasn't best hunting, dogs lay low when it's that cold but it's better than not hunting haha

30 below , I've not had any problems. 45 below ambient, I've had massive pressure increases.
In both rifles and revolvers.

 

[Deleted member 107796]

With so much data from hunting in extreme cold, like those regularly hunting in Alaska or other (ND comes to mind), I think any issues would have popped up. Unless maybe with handloading to maximums. I would guess humidity issues with unsealed primers might also be a factor.

 

[mountaincarver]

I will go from sticky bolt lift to easy bolt lift by pocketing my shells when in about 0 degree weather. its tough to get good reliable data when its cold as hell.

 

[Ndfarmer]

especially that Finnish guy they called white death. He would lay for hours under the snow waiting to make his shot

It's crazy how much the snow can insulate you from the cold, especially if their is wind.

 

[shaughn]

Was out on Wednesday checking on the missing bull...only to get a call from my aunt that he was in the calving barn....apparently 2500 pounds of cold red Angus bull can squeeze thru a half door that wasn't latched properly.....the digital thermometer indicated -47F on the N side of the barn...so can't really blame him...thankfully someone else has to get him out

I think part of most Military ammunition testing includes -40F testing..I know the Mk248 Mod 0 had to be under SAAMI spec pressure at that temp. testing temps were 70F 125F -40F.

Have been out on survival courses where temps got down to -30F not nice, even with proper arctic gear..I have shot rifles in those temps but prefer to be at home looking at the window drinking a cup of coffee.