Powder Temp. AB Mobile

[Canuck257]

This is probably a dumb question relating to powder temperature and muzzle velocity variation caused by temperature changes, but it's an area I have never explored.

How critical is the powder temp. and MV variation data to an accurate result? Also, is there a correct way to measure these two parameters?

 

[DocUSMCRetired]

This is dependent on the stability of your powder. A more temperature stable powder means you will benefit less than a less temperature stable powder.

So if your are using say Hodgdons Extreme powders you will see less of a change then if you were using say IMR 4064, just for example. You would need to measure the stability of your powder or the factory loaded ammunition you are buying to determine how much it helps you.

For example, using my personal weather logs. If I use the weather from July 18th last year, and then from today. And I see a 40 FPS shift from powder sensitivity(Randomly Made up Number for this example). That is a 6 MOA shift at 1000 yards or 60 inches. Do note, this is just an example with rounded numbers, and not actual live fire logs, I used a weapon I already have set up, weather logs, and AB Analytics to simulate the changes, and as such is not data from Applied Ballistics but simply an example. You can try this on your own, using our online ballistics calculator. Simply locate weather logs, set your weapon up, and change the muzzle velocity to test changes inside of the ballistic calculator I will provide below. Remember these are simulated numbers, and you won't know the "truth" until you field test your own weapon and ammunition loads.

Things to pay attention to. Pressure is Station Pressure not Barometric. Change your Temp, Pressure, Humidity Muzzle Velocity appropriately for the time of year you are checking. Muzzle Velocity should go down as it gets colder, Pressure should go down as it gets warmer. You can find powder temperature sensitivity tests all over the internet, however you won't know the actual results until you do this for yourself. With anything in reloading lot numbers play a role.

http://appliedballisticsllc.com/ballistics/

 

[Canuck257]

Thank you for a very clear and comprehensive reply. I'm using Hodgdon H1000 which is reputed to be very stable. Yet another excuse to put more rounds down range!

 

[seymour fish]

Canuck, Another potential way to analyze this is to use Quickload to carefully model your proven best load, paying attention to matching proven chrono MV via Ba and start pressure (modify upwards if into the lands), to arrive at barrel time. Then simply define the barrel time of powder charges at the upper and lower boundaries of your ladder node, and adjust for powder temp to determine the range of temps within which you remain within the node using your best load. Doing so will raise questions as to the veracity of powder temp sensitivities accepted as common knowledge, and may prove useful. Seymour

 

[JPeelen]

What is lacking in my view are independent velocity measurements of temperature insensitive propellants. All we have, as far as I know, are figures from manufacturers.