Cold Weather: Powder or Chrono Slowing Down?


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DanTheFarmer
January 12, 2013, 05:02 PM
Hi Guys,

Just back from the range. We're having a January Thaw up here in New Hampshire but it still quite a bit colder than when I was last developing loads in October. Had to cut the session short. The warm air over the cold snow was producing heavy fog.

My new loads were slower than expected, and some of the same, or at least very similar loads, as I shot in Oct0ber were slower as well.

What is your sense, is the powder burning slower for a lower MV? Is the chronograph slowing down in the cold (it was within its published operating temperature range and the battery "should" be good)?

Thanks for any input.

Dan

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tightgroup tiger
January 12, 2013, 05:26 PM
I would think the fog would have more affect than the temp. The fact that there is fog would mean that it had to be above freezing when you were shooting and I don't think you would see "wild"variations from 32deg and above from temperature sensitivity of powder.

The water particles in the fog is moving through the Chrony while you are shooting and probably making noice in the electronics.

Try those same loads again on a clear day, it's supposed to get cold again after the weekend that will get rid of the fog, and see if the numbers are better.

cfullgraf
January 12, 2013, 05:46 PM
During the cold, the electrons in the chronograph move more slowly causing the lower velocity.:)

Actually, in many cases, the lower temperature will slow cartridges down. How much? I do not know if there is a rule of thumb for that.

It is good if a load is developed in cold weather to check for overpressure when the ambient temperature warms up.

I am sure humidity also has effect as well. many folks record temperature and humidity when developing loads.

1858
January 12, 2013, 06:32 PM
Primer brisance is temperature dependent and powder burn rate can be too. Both can affect velocity. I seriously doubt that it's a chronograph issue. I was shooting some Remington .338 Lapua Mag a couple of weeks ago when it was in the low 40s and the ammunition was about 100 fps below the advertised MV. I don't have any data to compare it to so I have no idea if that load would gain 100 fps on a 70°F day but I wouldn't be surprised if it did given the amount of powder in the case.

Lost Sheep
January 12, 2013, 06:55 PM
Theory: Chronograph records lower velocities at low temp.

Test: put your chronograph in the refrigerator overnight, then take to the range in an ice chest on a normal-temperature day. Set up the chronograph and shoot over it before it warms up.

Do the same thing on a cold day, but keep the chronograph in a warm ice chest on the way to the range. Set up the chronograph and shoot over it before it cools down.

Do both with ammunition and gun kept at the SAME warm temperature (think a pistol worn inside your jacket for the cold day).

Potentially you might repeat both experiments with the ammunition and gun at the same cold temperature.

This should give you enough data to figure it out (except for the fog/humidity part).

Publish your data here. I will look for it this summer.

That's the way to PROVE the results.

My THEORY is that the chronograph will be consistent over its design temperature range (and the battery is FRESH!!!)

I could simplify my test of this theory by taking a box of match/target grade 22 rimfire ammo. Keep half the box warm, with the gun, and shoot them over the chronograph, then wait long enough to let the gun and the other box of ammo cool down. The chronograph during each string of shots must be at the same temperature as the chronograph was for the other string.

Thanks in advance.

Lost Sheep

Hondo 60
January 12, 2013, 07:06 PM
I seriously doubt the chronograph is slower in the cold.

I have heard from powder manufacturers that so&so powder is temperature insensitive.
To me that means some ARE temp sensitive.

One way to find out is to email or call the powder maker & ask.

JLDickmon
January 12, 2013, 07:21 PM
What Hondo said...

your powder is temperature sensitive.

BE glad it's one that slows down in the cold.. some speed up. And THAT can cause shenanigans.

HighExpert
January 14, 2013, 01:24 PM
I have shot bullseye for many years and as such have worked up light loads which are more sensitive to temperature as far a cycling the action. The following is an example.

.45ACP
SWC 200gr (National)
3.5 (Hot) to 3.7 (Cold) Bullseye
1.241 OAL
Match

This was to maintain the same zero at 50yds and to work the action reliably. Hope this answers your question.

Goattman
January 14, 2013, 02:07 PM
I posted a similar post a few days ago. My .308 handloads were running 2480 FPS with 42.1g IMR 4064 with outside temperature around 35 degrees. My BH match ammo was 2650 FPS in the summer. I was expecting my handloads to be closer to this. I received a number of responses. I did additional searching on the Internet (so we know it's true BONJOUR!) and found a spec that stated that IMR powder is effected by temp to the tune of 1.7 FPS. This supports your findings.

Not to hijack your thread, but assuming this type of claim is true, what does everybody do to deal with this?

1. A buttload of known data points?

2. Math?

3. Change your loads

4. Keep your ammo in your pocket?

5. Something else?

minnesota
January 14, 2013, 07:57 PM
I have been checking the velocity on some of my hand loads from fall to current and their has not been too much variation as of yet.

1SOW
January 14, 2013, 11:12 PM
Some powders are sensitive to temp change and some less so.

Essentially the speed of light doesn't change--it's not the chrono.

ArchAngelCD
January 14, 2013, 11:27 PM
I would think the powder is much more likely to react to the cold than the Chrono. If the variation is unacceptable give one of the Hodgdon Extreme Rifle Powders (http://www.hodgdon.com/extreme.html) a try. They are formulated to be temperature insensitive.
Our exclusive line of extruded rifle powders – Hodgdon Extreme™ – was developed to give shooters consistent performance, load after load, in even the most extreme heat and cold.

Which powder are you using and in which cartridge?

blarby
January 14, 2013, 11:36 PM
Or, again, just use H4895.

Lol.....

Nalgi
January 23, 2013, 11:16 PM
That's why they make 8208XBR its not temp sensitive! There are may articles that detail the variation in velocity due to temp. On normal shots it probably doesn't matter that much but if you are shooting 500 yds or farther it would.

:rolleyes:

Float Pilot
January 24, 2013, 03:30 PM
Here in Alaska, we have places where it will get to 70 below zero in the winter (Fort Yukon) and then be almost 100 degrees above in the summer (again, in Fort Yukon).

A 170 degree temp swing really makes you pay attention to your loads. Some powders and some primers are very temp sensitive.

Even in areas of Alaska like mine where the max cold in winter is only 35 below zero in winter and the max summer temp is around 80 degrees I still have some interesting velocity spreads.

I wish the OP had posted the velocity differences.

While cold temps will not slow down a chronograph,,,, the cold temps will affect the battery and electronics and give you more FALSE readings. ( I shoot twice a week in the winter)

The Sun angle will also give you odd readings. Chronographs work by reading the shadow of the bullet, so a low angle sun in winter will sometimes give weird or false readings.

The same goes for snow on the ground and bright sun.... That will cause the light top reflect back up onto the bottom of the bullet and you will not have any shadow. Thus no readings or weird readings.

Fog or mist, ( which by the way anyone who lives in a cold place can tell you that it can happen far below freezing, we call it ice-fog) will also cause the light to defuse and ruin the clear shadow effect that the chronograph needs to work correctly.

steveno
January 24, 2013, 03:34 PM
this is why you don't come up with a max load in cold weather and then shoot it on a hot summer day. you will have pressure problems

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