Digital Thermohygrometer


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  • The humidity level of propellant/powder has a major influence on its burning characteristics, which ultimately controls bullet velocity, and therefore affects accuracy and trajectory;
  • Research by Rheinmetall Denel Munition (Somchem) indicated a minimum bullet variance of 2.4 ft/sec for every 1% powder humidity variance for S335 (2.4 ft/sec per 1% humidity variance);
  • My own independent tests with S335 indicated a minimum bullet variance of 2.8 ft/sec for every 1% powder humidity variance (2.8 ft/sec per 1% humidity variance);
  • In my tests, the lowest (driest) powder humidity was 23.4% and the highest (wettest) was 89.1%.  This falls totally within range of the natural and seasonal humidity fluctuations for the inland.  I kept ALL other aspects of the loaded rounds the same, EXCEPT for the difference in powder humidity. The above humidity difference resulted in a velocity drop of 528 ft/sec AND a drop of 700mm on the target @ 300m;
  • Except for powder humidity variance, I don’t know of anything else I can do in reloading that will produce such drastic and poor results;
  • Somchem, other powder manufacturers and I recommend that it is always beneficial to control the humidity of powder during storage and use. Consensus are that the powder humidity should be kept between 30% and 60%;
  • The bullet velocity variance of 2.8 ft/sec could be even much higher when outside of the 30% to 60% humidity zone;
  • Potassium Carbonate (K2CO3Kaliumkarbonaat, maintains the humidity at a level of 43% inside a sealed container.

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