All about Powder
In the world of smokeless powders for rifles, there are double base powders and single base powders. There is extruded (stick powder) and ball/spherical powder. Then there are powders that have coatings applied to them to make them more temp stable. All the Hodgdon Extreme line of powders are single base, extruded powder and have a coating on the powder to make them more temp stable, like H4350, VARGET, H4831, H1000, RETUMBO, H4895, etc. These work very well to help maintain match grade consistent ammunition year round.
Ball or spherical powder, is very small sphericals that are much smaller than an extruded powder. Therefore they have more surface area to react to temp change. In general, ball/spherical powders are more temp sensitive and extruded powders are less temp sensitive.
Then there’s double base and single base powder. Single base powder uses only nitrocellulose, where double base powder uses nitrocellulose and nitroglycerin. The double base powders have more energy than single base powders do, therefore give higher speeds than single base powders do. Double base powders are more temp sensitive than a single base powder is. Double base powders will push a bullet faster than a single base powder will since there is more energy in the powder.
The Hodgdon Extreme line of powders are single base, extruded, and coated to be more temp stable. They are not immune to temp sensitivity, but they certainly are much better than other double base, ball/spherical powders.
So, if ammunition is loaded with a double base, ball/spherical powder, it has all the right combinations to VERY temp sensitive. Ammunition loaded with a double base, ball/spherical powder combination can push a bullet faster, but it comes at a cost. During the summer time, you risk blowing primers and locking up your bolt due to a high pressure round. And during the winter time, the velocities will be reduced creating much slower speeds. In either case, there is enough effect on the speeds and pressures to take you in or out of an accuracy node. This double base and ball/spherical powder combination is common on a lot of factory ammo. Ball/spherical powder is commonly used because it is easier to meter through progressive loading machines than an extruded powder.
I have used double base and ball/spherical powder combination in testing for a local guy in his 270 WSM. At his request, I used this powder. I was able to get over 100 fps more velocity than other Hodgdon powders with the same bullet. I worked up the load when it was cooler out. He shot the same load in the summer time and was blowing primers, locking up his bolt and groups opened way up. So, we went back to the load with a slower velocity with H4831 that was a temp stable load and still shot very well.
For this reason, I will not use any double base, ball/spherical powders for my custom match ammo. It’s too big of a risk with those powders, unless you reduce the load enough to shoot them in the summer time heat. But even then it can make for a bad shooting load. I load mostly Hodgdon Extreme powders for the better temperature stability and more consistent ammunition year round.
If you research each powder on the manufactures website, they list the kind of powder it is and you can see in the powder description and product details. Often times, these powders can shoot good, but you just can’t go to max and keep it there in year round temps.