in several previous threads, i've seen several references to difference in ammo performance, based on ambient temperature.... what effect does it have???... it's a sealed case, with a given displacement, a given propellant charge, a given projectile weight....so what changes to make a difference????

Increasing the temperature increases the pressure and that increases the velocity. However the pressure increases faster than the velocity. Therefore it would be a bad idea to work up max loads in the winter then use them in the summer !! It's also a bad idea to leave ammo in the sun !

You will also find that some powders utilized by reloaders are far more sensitive to extream temp changes than others. A couple of IMR powders I used to load AR-15 match ammo worked great in the winter but would blow primers out in the summer here in Phoenix, AZ. Read up on the powders befor you load.

quote:

Originally posted by 458Lottfan:
You will also find that some powders utilized by reloaders are far more sensitive to extream temp changes than others. A couple of IMR powders I used to load AR-15 match ammo worked great in the winter but would blow primers out in the summer here in Phoenix, AZ. Read up on the powders befor you load.

Hell, the cartridges will detonate by themselves in the heat around Phoenix!


Most powders today are not as sinsitive to temp changes as those of the old days of CORDITE! For a loads that will not over pressure,one can simply fly to PHX in July to work up loads, and they will work fine on the even on the sun.

All kidding asside, one should work his max loads in hot summer, and then make sure you know where they shoot in winter! I've used loads done this way in invirons from below zero, to 110 degs F with no problem!

Temperature differences do make a difference. As a rule of thumb, for each degree in temperature change it will change the the velocity 1 fps. Example: If I am shooting my rifle in 50 degree weather and I'm getting a velocity of 2150 fps then I go to Africa and its 90 degrees then the velocity will go up 40-50 fps. If I am getting ready for an Alaskan hunt in the fall and I'm sighting my gun in August in southern Texas in 95 degree weather I will loose 50-60 fps if the weather in Alaska is 35 degrees. Again, this is not rocket science just a guestimate. Chrono in the heat and in the cold and you know exactly what is going to happen with your gun.

I always use Hodgdons Extreme line of powders if I can in my doule rifles. They are very stable with changing temperatures.

465H&H

Historically, Kynoch offered a so called "Tropical load" often shipped in soldred lead or tin outer packets for use in tropical and sub-tropical countries, these loads had as a general rule a reduction in the Cordite charge of around 5 grains or so and reflected the effects on pressure and velocity that extreme heat and humidity had on Cordite powders.

Double rifles would be regulated in England (or Scotland of course!) for the normal cordite loading but if shipped to india or Africa could be supplied with the Tropical load, the theory being that the rise in temeprature would cause the cordite to burn hotter and thus generate more pressure, hence by reducing the charge, the temeprature change would make the rifle shoot to the more usual pressure and velocity and hence shoot to the pont of regulation.