Powder temp vs ambient temp in ballistics app?

[JS624]

Hey guys dumb question here but why in most ballistics app that I've used at least there is a powder temp value and also ambient temp? Wouldn't they be the same?
if I'm missing something can you tell me what to input for the powder temp value.
thanks

 

[Fursniper]

The difference is if you use the optional input of powder temp you should also input your muzzle velocity (which there will be an input field for). Then your base powder temp correlates to that specific MV. In future ballistic calculations for that specific ammo profile you can then enter a new powder temperature (assuming it is different from what you originally entered) and your program will automatically adjust your MV for the new powder temp. The ambient temp input is needed & there because your program needs that input to help it determine the speed of sound as part of determining the ballistic solution from all of your inputs for the solution. Some people use the optional inputs & some dont. The tricky part is because different powders react differently to temperature changes & the programming for determining changes in MV based on temperature changes can not account for the wide variation in the range of powders so having the program determine that for you can give you a new MV that may or may not be correct. That's my understanding of it anyway. Hope my explanation makes sense & helps some. The best way I know of to determine changes in MV is to simply chrono your load at different temperatures and compare that to the optional inputs and see how accurate your particular ballistic solver is compared to actual MV for the type of powder you are using. A labradar for instance makes this really easy to do.

 

[strikeeagle1]

The powder temp and ambient temp inputs would be the same if you acquired your muzzle velocity data contemporaneously. As you log new and different ambient temperature and corresponding muzzle velocities, you can then determine how your "muzzle velocity variation" with ambient temperature, usually recorded in fps / deg temperature; a 100 fps difference with a 20 deg difference would be 5 fps / deg. If you use the same ammo and get several different muzzle velocity variation-ambient temperature pairings you can establish a fairly accurate fps/deg change that can be entered in the ballistics software. THEN, when you are on the range with only knowing the current ambient temperature (and no new muzzle velocity acquired that day), the ballistics software will adjust with a corrected muzzle velocity, based on prior data, for your current station temperature.

 

[JS624]

Thanks guys

 

[LastShot300]

Just will add that the new calculated MV is only good for the the first two shots. After that, barrel heating will change MV.