Colder weather reduces velocity...

350 Mag

350 Mag

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I went to the range today(-5 Celcius).

My reloads(with same amount of powder) were 70 fps slower than when I went to the range in August.(+18 celcius).

The powder was Hodgdon H-1000.

Has anyone else experienced this before?

The P.O.I shift was a little different but nothing to write home about.

My Speer manual has a temp comparison chart and it appears from 70 deg F to 30 deg F the difference is around 75 fps less.

Interesting info.

My question:

When developing a load can one safely exceed listed values in manuals if your developing a load for Late Season Deer where the temps can be -20?


Nothing else has changed so pressures must have dropped in order to reduce velocity.









.
 
Yes Temperature makes a difference when it comes to pressure.....a load I had worked up in 15c degree weather became over pressure at 30c, not doing that again.

Back to the actual question, I would not assume that going above max will be ok if its colder, Im not personnally going to bet on it. Work up the load again when its colder if you want the velocity, only safe way to do it as far as Im concerned.

Its an interesting thing, Im sure one of the old timer will be able to shed some better light here.
 
350 Mag said:
My question:

When developing a load can one safely exceed listed values in manuals if your developing a load for Late Season Deer where the temps can be -20?


Nothing else has changed so pressures must have dropped in order to reduce velocity.



.
Click to expand...

Sounds simple, but how do you develop the load properly unless you do so at the temperatures you will be shooting at? And then what happens if it's unseasonable warm during season?

Do you really want to categorize your ammo based on outside temperature?
 
joe-nwt said:
Sounds simple, but how do you develop the load properly unless you do so at the temperatures you will be shooting at? And then what happens if it's unseasonable warm during season?

Do you really want to categorize your ammo based on outside temperature?
Click to expand...

Yes your right...I guess it is best to air on the side of safety.

A guy would have to be careful.

I know this REALLY applied to Handgun loads but was unaware there would be that much difference in rifle loads.

This is especially strange because H-1000 like other Hodgdon powders are supposed to be temperature stable?
 
Cold air being slightly thicker than warm air will also slow your bullet down. Do you really think the dear, moose (Insert beast here) will notice the 70 or 75 fps difference when the bullet hits him/her? As mentioned above, do not "Up" your warm weather loads to gain that little bit extra, it could be very bad. What if your box of reloads sit in the sun for a couple of hours?

Scott
 
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This From Steve's reloading pages, he's a member here....

Effects of Temperature on Velocity and Pressure

Velocity and pressure are both measurably affected by temperature.

The following chart was worked out by the famous big game hunter, Les Bowman, of Cody, Wyoming. Les has the following to say about this effect:


"Few handloaders realize the difference temperature of powder makes in velocity and pressure. And the funny thing is that the top temperatures, that is from 72 degrees normal to 100 degrees for instance, affects pressure more than from 70 degrees down to zero. As you will notice in the chart, there is a 129 fps minus for the zero temperature reading at 4000 fps bullet speed, and 155 fps plus for the temperature about 70 to 100. Many sight in one day when it is a certain temperature and later, when temperatures are perhaps 50 degrees different, they think their scope has changed when groups print at a different place. Also maximum loads worked up at, say 40 degrees, can be really dangerous at 90 or 100 degrees. It's the powder temperature that counts, not the temperature of the outside air. I have had a lot of correspondence with DuPont and was told by them that they figure 60 p.s.i. in pressure difference for every degree in powder temperature change. In the case of the 4,000 fps above at 155 on the high side and 129 on the low, or a difference total of 284 fps, that would make 17,000 pounds difference in pressure. This is the correction chart I use, and while I do not claim it is absolutely right, it is close."


Temperature Correction Chart Used by Les Bowman


Add This To Tested Velocity Tested Temp Subtract This From Tested Velocity
100'F 90'F 80'F 70'F 60'F 50'F 40'F 30'F 20'F 10'F 0'F
85 56 24 2300 18 36 50 54 57 66 80
90 58 25 2400 19 37 50 56 60 70 84
96 60 26 2500 20 38 51 58 65 77 88
101 62 27 2600 21 39 52 60 69 89 89
105 64 28 2700 22 40 54 62 71 81 90
108 65 28 2800 23 41 56 68 77 85 91
112 66 29 2900 24 43 58 70 78 88 94
116 68 30 3000 25 44 60 73 83 91 97
121 71 32 3100 25 45 61 74 85 93 98
124 73 32 3200 26 47 63 77 92 96 102
126 75 33 3300 27 48 66 82 94 101 106
132 77 34 3400 28 50 68 82 94 102 110
135 79 35 3500 29 52 70 85 86 106 113
140 82 37 3600 29 52 71 86 98 108 115
144 86 38 3700 30 54 73 89 101 111 119
147 87 39 3800 31 56 74 91 104 114 123
151 89 39 3900 33 57 78 94 107 118 126
155 91 40 4000 33 59 80 97 110 121 129



Copyright 1998-2008 Stephen Ricciardelli
 
Cold air is denser than hot air, thus more friction. So it will affect your bullet tracjectory for sure.

Depending on your powder, it will also affect muzzle velocity. But there ARE temperature insensitive powders out there, at least some that that are much less affected by temperature variations than others.
 
During WWII the Germans were shelling Leningrad with24cm guns. In order to increase the range the powder caharge and the gun were preheated in order to increase the range.
 
I was thinking of a potentially dangerous scenario if I pursued this...

Say I worked up a +P load for -20 Celcius...and everything is hunky-dorry.

Now...

If I was driving across a field and my ammo was in the confines of a nicely heated pickup truck...All of sudden HUGE buck is 300 yards away. I quickly jump out. Use the truck hood for rest and BLAMMO...case ruptures.

The powder(which was loaded for -20 Celcius) was still +15(from inside the truck)...cause pressure spike.

I guess I will have to mount ammo holder on outside of truck...LOL...or I will just accept the 75 FPS loss.

I just put this info out there because I found it interesting that 20 deg temp swing affected velocity much more that I thought....especially with the Hodgdon powder.
 
It seems that the Austrialian temperature stable powder marketed by Hodgdon works well in the heat but not so well once it gets really cold. I hope that is not the case with Hybrid 100V. This stuff is also marketed by Hodgdon, but is made by St Marks Powder in the States. According to their data its produces consistant results to -40. Won't be long before I can test that.
 
Temperature sensitivity varies considerably from powder type to powder type. [and always has] I personally don't believe there is any powder that is not affected somewhat by extreme temperatures, particularly when temps are way, way down there. I think it is an excellent idea to shoot the load you will be using in cold temps to see how trajectory is affected, since velocity loss can cause misses due to bullet drop, particularly at longer ranges. First shot from a cold rifle will be the determining factor. I have a particularly accurate load in my 30-06 that goes completely to pot, accuracy-wise when the temperature descends below -20ºC. I have not abandoned that load, I simply use something else when I anticipate hunting in really cold weather. Regards, Eagleye.
 
I work up loads at around 20 degrees C and then test for pressure signs at 30 degrees C,as I never hunt in warmer weather than that.I then test at -20 degrees or so to see if the accuracy holds up at colder temperatures.Using this procedure,temperature differences do not result in any safety concerns.
 
Eagleye said:
Temperature sensitivity varies considerably from powder type to powder type. [and always has] I personally don't believe there is any powder that is not affected somewhat by extreme temperatures, particularly when temps are way, way down there. I think it is an excellent idea to shoot the load you will be using in cold temps to see how trajectory is affected, since velocity loss can cause misses due to bullet drop, particularly at longer ranges. First shot from a cold rifle will be the determining factor. I have a particularly accurate load in my 30-06 that goes completely to pot, accuracy-wise when the temperature descends below -20ºC. I have not abandoned that load, I simply use something else when I anticipate hunting in really cold weather. Regards, Eagleye.
Click to expand...


Great Post....

It is another factor that comes into play...I am going to try and find a load that comes close to 3000 fps....
 
Children... settle down.

When I worked at CIL ammo R & D, part of the test of every proposed factory loading receipe was to cold soak the ammo for 3 days at -40 and then test fire it. We had little insulated boxes to carry the ammo from the freezer to the range. Velocity drops were 100 to 300 fps for shotgun and sometimes even more for rifle.

Temperature issues are very real. The big varaiable is the nitroglycerine content of the powder. Single base powders (no nitro) are less sensitive than the double base powders. If you are developing a hunting load that has to work in warm wx and cold wx too, use a single base powder and use a magnum primer. Thsi ammo will drop less velocity in the cold.

It is also important to swish the bolt out in Varsol and shoot it dry, or with just some moly powder. Oil can slow down the primer stike in the cold.

We tend to do our rifle testing and load development in the spring, becasue we are so glad to get out of the house again and back onto the range. Such ammo can wind up too hot in August and blow primers, etc. here is what I do in the spring if I am not shooting indoors. I take the ammo to the range in picnic cooler. In the cooler are two 2 litre Coke bottles filled with hot water from the tap. This keeps the ammo toasty. Then, when I test the ammo, in 5 or 10 shot groups, I put the ammo in the shirt pocket. This keeps the ammo at around body temperature (hot) until fired. I then know the results are valid for the summer.

Hunting ammo. If you expect to face cold weather, or it is a possibility, use a single base power and a magnum primer. Temperature drop is an easy thing to test. Use your own freezer.
 
I find the hodgdon powders to be reliable in hot or cold weather, and the Aliant to be the most unpredictable in temperature change, but to be honest the only place i notice a difference is on paper as the POI changes with my 6.5x284 and 6mm brs and PPCs.

When shooting strings in tactical shoots you will not see the guys leave the shell in the chambers to long on a hot gun, this does increase the pressure enough to throw a shot at long distance.

I just have not had any issues with temp, I do load my max loads in the summer months to test them, I figure if I run them hot on hot days I should npt have issues in the 0 degree days of fall.

A quick test if you ever have a chrony set up is to run 2-3 cold shots though than continue to shoot, when the gun is good and warm chamber a shell and let it sit for a min, extract the shell and feel it, it will be warm, if you chorny it you will see a slight increase in velocity due to pressure.
 
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