What I am saying is that the atmospheric conditions have just as much if not more of an effect on the charge than just the chemical make-up of the powder alone.racesnake said:
4350, IMR vs H in 6XC
- Thread starter VooDooMagic
- Start date
There may be some confusion over internal ballistics vs external ballistics. The temperature of the powder affects the muzzle velocity. While the air temperature affects the bullet in flight - warmer air has less drag.
Powder temperature can be affected by the cartridge sitting in the sun, or in a pants pocket, or even sitting in a hot chamber. I have seen the last shot in a five shot string be 20 or 30 fps faster muzzle velocity just by sitting in a hot chamber for a couple minutes.
Powder temperature can be affected by the cartridge sitting in the sun, or in a pants pocket, or even sitting in a hot chamber. I have seen the last shot in a five shot string be 20 or 30 fps faster muzzle velocity just by sitting in a hot chamber for a couple minutes.
This is an example of my personal experience in using TAC powder for XTC ammo. I have been told numerous times how temp sensitive TAC is and basically it's junk powder so I decided to test the theory. Last summer I went to the range to chrono my loads against the data I had gathered earlier that year. It was a good hot day with temps. in the low 90's and high humidity. I chrono'ed 10 rounds to get an average FPS along with ES and SD. Before I started I took 10 additional rounds and laid them on the concrete pad in direct sun. Time was 12:30 noon. About 30 min. passed while getting the info on the 1st 10 rounds plus some time to let the barrel cool. Firing the next 10 rounds I had less than 10FPS difference for an average velocity and did not have any pressure signs. These rounds were almost too hot to hold in my hand. Just so that you know that my loads are near max. and don't try them in your rifle without starting lower and working up. I use WCC brass with Tula SRM primers 24.8gr. of TAC powder with a HBN coated Berger 80VLD bullet seated .010 into the lands. I know this is not scientific but for me I feel confident that my choice of components will serve me well. I believe the difference people are seeing in their elevation settings from the cold to hot temps. is because of the atmospheric conditions and not the powders temp. Lighting conditions will cause changes in elevation, the way the sunlight hits the target causes changes. I could be wrong but until scientific proof comes out I'm sticking to what I have found.
+1 Bill, You're exactly right that there are two things going on here...internal ballistics and external ballistics. Separate issues but definitely connected. IMO, if you let a round sit in a hot chamber for a bit too long during a rapid fire run, the POI will most definitely shift on you. If I can't get the round down range within about 10 sec. I pull it out and wait for the proper conditions.
Eric in DL
Eric in DL
[br]WyleWD said:
So, what do you think is the lesson learned? Don't leave your gun in the sun? Always wear shooting glasses? Reloder 15 is temperature sensitive? [br]
Do you know the root cause of the failure? While not likely, it could have been a cause other than temperature. If a load is near maximum pressure, it pays to be aware of external factors. Steve made several mistakes and it should serve as a reminder to pay attention to each shot. If something seems different, it probably warrants investigation. No match is worth a destroyed gun, let alone an injury. [br]
My matches may require shooting up to 30 rounds in 25 minutes when the temperatures are near 100°F. Barrels do not cool well in those circumstances. Even when using single base powders, I look at weather forecasts and sometimes adjust the load to compensate. Keeping careful notes of conditions present when a load is developed and knowing the powder characteristics enable informed decision making. There are a lot of variables in reloading and shooting. Some we can control, some we cannot. Knowledge of the relationships and consequences keep us safe. Some of that knowledge comes from scientific information and some from others' experience. Regardless the source, I don't need to blow up a gun to know what I should and should not do.
[br]WyleWD said:sleepygator, good post, and you had so many questions in there that I answered / commented in red itallics in the quote.WD
The questions were rhetorical. Sorry I did not make that more obvious. I have been on engineering teams from pistols to 155 Howitzers and have some appreciation of the dynamics involved.
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