REVERSE TEMP SENSITIVITY????
- Thread starter Calvin45
- Start date
Help Support Long Range Hunting Forum
Calvin45
Well-Known Member
Hmmmm…very interesting theory. Will have to chew on that for a while.
Superformance isn't advertised as temp stable but that could be.
memtb
Well-Known Member
Yep….not a true test unless everything is at ambient! memtb
Calvin45
Well-Known Member
Agreed. It was tho. All my stuff had been overnight in my dads truck when I tested it. All the same temp and cold together.
Depending on cartridge up to 10 rounds in a 223 or the like but 7 RUM about 3 or 4. It lasts long enough that you need to consider it for the cold bore shot out hunting.
RegionRat
Well-Known Member
You are correct.
When we build and test guns on the ground at near room temp, imagine how nice and cold they get when they have been cold soaked at altitude!?!
Temps on the guns that fly on aircraft go through horrific temp swings. Yet, the effects on the powder are more of a concern than those of the barrels/chambers.
Last edited:
Calvin45
Well-Known Member
Woah that's a great point I wouldn't have thought of. But yeah…aircraft guns…the barrels aren't a problem
One shot down a magnum-sized cartridge probably raises the ambient barrel temp ~20F, from a barrel starting testing at 0F.
Which is another reason why I say most guys never bring their barrels down to outside ambient temps when collecting MVs.
After 2 shots, any magnum cartridge barrel is now heated 30-40F. It takes a lot of patience and time to let a fired barrel drop back down to cold outdoor ambients temps. So long that when I tested powder temperature sensitivity, I'd try to take at least 3 rifles. So one rifle could chill back down again while rotating thru the rifles. Even then there was a lot of thumb twittling involved. Hurry up and wait...
That is not a good analogy or comparison, the guns on fighters are not shot for group. That said, ammo and the gun design DO take into consideration the temperature they will be used at and they are extensively tested under those conditions to ensure proper function at those extreme variations.
Calvin45
Well-Known Member
Not arguing but I wasn't shooting for groups either. I was testing velocity and function and found something alarming.
You're not alone, 8133 has an inverse relationship to temperature. Dunno why. My 7 mag load gains 55fps from 85f to 20fHey all, I brought this up in my imr 4831 thread but it deserves its own thread.
Anyone here observe such a thing as reverse temp sensitivity? Cuz I have and it puzzles the heck out of me. Like the Grinch who stole Christmas I've puzzled and puzzled till my puzzler was sore!
Both loads in 300 win mag.
One is 8133 under a 225 eld m
The other is superformance under a 120 Barnes tac tx.
Bullets and bore are hbn treated
Both loads worked up in the summer months in Saskatchewan. Figured that's be a guarantee of good to go in winter, just might lose a little velocity. Nope. So weird.
Two winters now this has happened, and last summer the loads were absolutely fine again so it's not cold welding or any other nonsense about shelf life.
In the summer, like 27 celcius or 80 Fahrenheit I think, it was a 120 tac x at 4050 fps. In -17 or right around 0 Fahrenheit or so, it was 4160 fps and I had to tap the bolt open!!!!!
Same conditions with the eld m 8133 load and in the summer it's 2760. In the winter it's doing 2830 and the bolt is ever so slightly sticky.
And I've done this with other bullets treated with hbn and different powders, doesn't happen, got nothing to do with hbn.
Doesn't happen with any of
The other powders I've used.
Experiences and theories welcome, let's shoot the breeze and maybe we'll learn a thing or two along the way.
What I was getting at is a 200 FPS variation on speed for the first few cold bore rounds is completely irrelevant on a aircraft mounted gun but very relevant on a hunting or target round.
I know a lot of people will not believe my explanation of why this is happening, I am fine with that. All I can do is provide the benefit of my experience. If someone comes up with a better comprehensive explanation I will be very interested to see it.
Here is one of the articles I read:
" The degree to which these propellants are flattened is carefully controlled to slightly stress the grains. This improves the cold temperature performance of the Ball powders. The stressed grains at cold temperatures tend to fracture somewhat, which increases the burning surface area slightly, increasing the gas production rate and reducing the pressure and velocity drop at cold temperatures. There is a fine line though. If the propellant grains are flattened too much, the pressure at cold temperatures can go up substantially."
www.gunsandammo.com
" The degree to which these propellants are flattened is carefully controlled to slightly stress the grains. This improves the cold temperature performance of the Ball powders. The stressed grains at cold temperatures tend to fracture somewhat, which increases the burning surface area slightly, increasing the gas production rate and reducing the pressure and velocity drop at cold temperatures. There is a fine line though. If the propellant grains are flattened too much, the pressure at cold temperatures can go up substantially."
Temperature Effects on Gunpowder Explained - Guns and Ammo
Have you shot ammunition in the winter without issue, only to experience stiff bolt lift and cratered or pierced primers in the summer heat?
www.gunsandammo.com
