Did you know? Powder moist content18.07.2018
Variations in moisture content change the burning rate of a powder and thereby chamber pressures and muzzle velocity. The moisture content of the N100 and N300 series powders is usually around 1 %, the N500-series’ normal moisture content is 0.6 % because of the added nitroglycerine.
So what difference does moisture content have? Here’s an example. In a test, a powder sample was dried by heating it, losing about 0.5 % of its weight. Cartridges were then loaded with the dried powder and fired using a pressure gun. Chamber pressures and muzzle velocities produced by these special cartridges were compared to those produced by cartridges loaded with untreated powder. (The powder charge and bullet were of course the same in both sets of cartridges.)
Comparing results showed chamber pressures increased from 320 MPa to 355 MPa with the dried powder, and the muzzle velocity increased accordingly from 770 m/s to 790 m/s (2526 to 2592 fps). And note, this is only one example, of one caliber and loading. The difference might be much higher depending on the cartridge and loading combinations.
What does this tell us? Well, it seems we need to forget the old saying “Keep your powder dry”! Instead, focus on proper powder storage, at a temperature below 20°C / 68°F and humidity between 55-65 %. Safe reloading everybody!