I have been involved with powder R & D. The formulations for each powder not only include the chemical content, but also the deterrent coating, how the powder is extruded and cut, how long it is tumbled (with graphite) and the water content.
Water content slows the power down. It is a big variable over time (fresh vs. old powder.)
Making a batch of powder is much like baking a cake with a recipe. A pinch of this, a dash of that, stir for so long, etc. and no two batches are exactly the same.
When a commercial buyer (military or ammo company) buys a powder, it buys from a longer list of powders than available to reloaders as “canister” powders. I would say the list of powders each company makes is about 4 times as many as they sell to reloaders. There are a lot more fine steps in powder speeds. This is why you should not open a commercial or military case and assume you can tell what is in it. Even if it is a powder you know, like 4895, the commercial grade 4895 can be a lot faster or slower than the canister grade powder.
Each commercial purchase comes with a thick set of test documentation, giving the user an idea as to how this batch compares to other batches, and then he develops his own loads.
If a batch is close to the specs of the cannister lot, then it gets tweaked to be sold as cannister powder (retail). Tweaking is accomplished by blending some lots (a little fast is blended with a lot that is a bit slow) and by adjusting the water content.
The problem with powder is the water. The power dries out. Leaving it in the powder thrower for a week will speed it up. Usually when reloaders complain that a lot of new powder is ‘slow” what they really mean is that their old lot was faster. Yes, it was, because it dried out. The only thing we can do is avoid leaving powder in the thrower, and make sure the powder is stored in a sealed container.
If you buy powder in an 8 pound jug, decant it into 8 one pound plastic bottles. These small ones remains sealed until used. If you keep using a big jug, the increasing airspace in the jug dries out the powder.
I buy powder in 20 kilo (44 pound) barrels. It gets decanted into 4 liter window washer fluid jugs and 2 liter plastic juice bottles. They are labeled with a black felt pen, so there is no danger of forgetting what is what. In this way powder holds its speed until used. Some barrels of powder are used in a week. I have some that must be 5 years old by now.
Most ammo companies sell their commercial powders using numeric names that relate to the powder speed, so you can get an idea of speed by the number. E.g. N135, n140, n150, N160, N165
The old IMR numbers (4198, 4756, 30301, 4895, 4350, and 4831) come from a different background. When you work in R & D you are issued a notebook, quite similar to the military message notebook. Every project you work on is assigned a project number and the all your notes note the project number. The idea of the notes is to be able to later find out what worked and what did not. Sometimes a test result may mean nothing for the current project but be important for the next. This was long before computers and data bases.
A project to develop a powder would be assigned a number, in sequence. Project #4895 was to develop a medium speed rifle propellant suitable for 30-06 that exhibited certain other characteristics, including storage stability, low muzzle smoke, low muzzle flash, etc. When the project was finished the resulting powder carried the project number – 4895. Who knows what project #4896 was? I guess nothing came of it.
Getting back to Varget. I seem to recall buying that powder as 2206 or 2208. It was/is an Australian military powder. I assume the military powders would vary from lot to lot but I would expect the Varget “canister” lot powders to all be very close together in speed. The only powder I ever found with significant variation was IMR4320.
If shooters find the current lot of Varget is slow, it more likely means that the old lot of Varget they had got faster as it dried out.
Powder burns more consistantly at higher pressure. If a bullet is fatter it will generate more pressure, and more vlocity and better results. the reverse is true. If the lapua is smaller in daimeter, it will take more powder to boost pressure, velocity and consistancy.
