Temperature effects pressure ?

[OregonCoyoteKiller]

Has anyone done studies to see the actual effects on chamber pressure due to temperature? I could theorize that keeping your shells in the truck where its warm until you shoot could help simulate warmer temps, but what effect does that cold air have on your powder burn rate even if the shell was kept in a warn area before firing. This rises the question about the shells not being the exact temp, velocity could vary, and accuracy will suffer. So maybe one could find the most accurate load and velocity, record it and at some point you could tailor the load to achieve the same velocity after temps have changed.

 

[Ol` Joe]

Hodgdon has worked with temp changes and pressures with their powders but how much data they`ll share I don`t know.
There have been a couple of posters on other forums that claim to have explored it also. One of the posters claims barrel temp can affect the powder just as ambient temp can. The few seconds the cartridge lays in the chamber allows the powder to start warming. He also claims to suspect the temp of the primer has more effect then the powder temp in some cases. Here is a link to some of his studies.
http://www.shootingsoftware.com/tech.htm

 

[7mmfan]

Bob Hagel in his book Big Game Hunting addressed this same issue by conducting a variety of tests with the same load in several different rifles and calibers over a wide temperature span. He found that according to extreme differences in temperature, extreme cold had the same effect as extreme heat. Some of the differences were very dramatic.

Brad

 

[Murphdog]

I was blessed when taught to reload by a guru :grin: . Papa has always said if you are going to be working loads up to near maximum levels do so on a hot day. In my experience he is right. My 30-06 with either the 165 or the 180's with Re 22 will flatten primers on the book max. on a 90 degree afternoon. On a cool fall day it willn't. :shock: Could working a load up on a cool day and then shooting it on a hot day get you in trouble? Don't know but I like to error on the side of saftey

 

[RDub]

I have found it very difficult to 'fake out' ambient temperatures that way working up loads.
I too have come to the conclusion that if you are going to work up a load that you will most likely shoot in cold weather, then work up the load in the same cold weather, as close as possible. And the reverse is true also. If you plan a hunt in warm weather then work up the load in the same warm weather.
Even factory ammo will prefer one temperature extreme or another. Rarely will factory ammo or a handload shoot well in ALL temperatures. It will be the case when you work up a maximum hunting load in cold weather, for cold weather, and you shoot that load in hot weather, you will see pressure signs.
The great part of handloading is being able to taylor loads for any situation or purpose we wish. But also as handloaders we must do what we must to be safe about it and be able to keep track of what load is what.

 

[steve4102]

When to the range this weekend and tried a little experiment with warm rounds and cold rounds.
Temp. 15 deg and calm
Rifle Rem 700 30-06
Load Winchester Supreme 180gr Fail Safes
Cold Loads (15 deg) 2575,2595,2584fps
Very accurate

Warm loads (kept in truck next to heater)
2631,2621,2620fps
Very accurate and POI unchanged

Load #2
150gr AccuBond 61.5gr Ramshot Hunter

Cold rounds: 2896,2885,2881
Warm Rounds: 2896,2905,2908
POI Unchanged

Load #3
150 AccuBond 58.5gr Ramshot BigGame

Cold Rounds:2965,2952,2944
Warm Rounds: 2989,2964,2951
POI Unchanged

As you can see the fps from warm to cold was minimal and POI was unchanged. It looks like the below zero shit is on it's way. I will try this test again when the temps are about 20 below and see what happens

 

[Jaywalker]

I did see some remarkable pressure changes with RL22 that I attributed to ambient temperature.

As an aside, keep in mind that the outside air temperature is not the only "ambient" temperature. Shoot your rifle a few times and the barrel and action are quite warm. Leave the cartridge in the chamber awhile before shooting it, and you'll have higher pressures, regardless of the outside air temperature.

In my case with the RL-22 and a Ruger M77 MkII 6.5x55, I was shooting a warm load, but not even at the top of the low-pressure reloading tables for that round. I tend to fire rifles faster than some do, however, and their chambers/barrels do get hot. In this particular circumstance, I fired three from a warm receiver. The first primer was flat, the second cratered, and, though I don't know why I fired the third, I did - it punctured. I pulled and measured the next two loads in that lot, and they were fine.

Looking back, I can't say whether the cause of that was the heated receiver on a 90-degree day, or possibly a headspace issue. I did give away a pound and a a half of RL-22, however, and moved exclusively to less temperature sensitive powders. I now use, exclusively, the Hodgdon Extreme line and may try out the Ramshot line or RL-15 (their only temperature-insensitive powder, developed for the military).

John Barsness has written of his tests wherein temperature-sensitive powders may lose 100 - 200 fps between 70 and 30 degrees. While that amount of velocity won't in itself make a difference in the bullet's game-taking ability, it might make a real difference in accuracy and point of impact. How many loads do we try out before we settle on an accurate big game laod? How many grains of powder does that 100 or 200 fps amount to? It seems to me like cheap insurance to give up the (possibly) small increment of velocity to the assurance that it will shoot the same way when I'm hunting in the winter that it did when I developed it in the summer.

Jaywalker

 

[LoneStar]

Benchrest shooters are well aware of this phenomenon and will adjust their charge weights depending on temperature. They are more interested in accuracy than velocity, but if accuracy tracks velocity then to maintain small groups you will need to adjust velocity through powder charge weights.

IME a 50 degree change in temperature will effect peak accuracy - it effects velocity dependent on the powder used. Speer published a temperature/velocity chart in their manuals for many years, and it indicated a definate difference in velocity as the temperature changed. How this chart fits with modern powders is not known.

 

[Blaine]

I found out about temp. effects on loads this fall. I spent all summer working up loads when the temp. was in the 70's & 80's. It didn't occur to me to check the loads when the temp was lower. Luckily, I decided to "double check" my scope setting before I actually hunted. The group was still almost as tight, but the POI changed dramatically. I adjusted the scope settings in time, but I will not let that happen to me again. This summer, when I load up and final test my hunting loads, I'm going to store my ammo on ice until just before shooting to simulate northern Maine's hunting weather. I didn't have a chroney available for the final scope check, so I don't know exactly how pressures/velocity was affected, but the POI was off by more than 4" up and right.

Blaine

 

[OregonCoyoteKiller]

Hey, All good input, I followed some of the links you guys posted and found some interesting stuff. One of my biggest concerns was when I shot some of my reloads from cool weather to hot, and I felt I was exceeding max pressures,bold opened hard and shaved brass on bolt face. When it wasnt like that before (same batch of ammo). One study suggested primer temps having more effect than powder temp. What I have learned is that its worth double checking if the temps will be different extremes. But dont expect more than a couple hundred fps.
Thanks for all the input.
OCK