What affects Smokeless Powder Burn Rates

[ET1]

The first thing a shooter needs to know is the principal behind powder burn rate. It’s not overly complicated. But what it reveals may surprise you.

Smokeless powder requires two things to burn efficiently, heat and pressure. Without enough heat the powder will not ignite.
Pressure is required as an accelerant. Smokeless powder burns faster the higher the pressure. Without pressure the powder will not burn completely or will burn very inefficiently.
The relation between temperature and pressure creates a feedback loop of sorts. Typically, the higher the temperature the faster the burn the higher the pressure.
If not, carefully controlled pressures using smokeless powder can quickly spike out of control.

The above is the basic concept but doesn’t include the other variables that affect the powder burn. Some of these variables:

• Size of burn chamber. Bore
• Volumetric expansion of burn chamber. Bore
• Strength of ignition source
• Mass of projectile being accelerated down the bore.
• Amount of powder being used

Now I can see some asking, “Why do I need to understand all this?”.
If you are using a proven given load only then you don’t need to know any of this. But if you are going to experiment with a load then you should be aware of what certain alterations will do to the pressure results.
Just a friendly reminder, if you get a load that you have to hammer down instead of pushing it through and decide to fire it, I can’t say what the end result would be but I know the pressure will be way up there.

[MikePal]

Plus powder shape and construction ??

[ET1]

Plus powder shape and construction ??

My thread intention was to focus on pressure released by the powder under certain conditions and some factors that can affect the end result.
The two items you mentioned deal more with the actual powder burn characteristics.
For shape I prefer short cut extruded powder and if possible single based.
As for composition this allows making powders with different burn rates for different requirements.
Now in the powder makers wisdom they have been using additives to make powder less temp sensitive to maintain consistent burn and pressure results over a wider temp range.
Now they are going one step further by adding an additive to reduce copper fouling, go figure, chuckle.