jimzim Posted July 20, 2012 Share Posted July 20, 2012 Hearing that WST is an inverse temperature sensitive powder, I wanted to see how much it drives the power factor (PF) when the ambient temperature varies. I fired two strings (controlled at two different temperatures) through a chronograph to determine the spread. Below is the result: TEST LOAD: Rainer 180 grain RNFP bullet WST Powder @ 4.5 grains Federal small pistol primer Mixed range brass (no nickel) roll sized OAL 1.142 Loaded on Dillon Precision Super 1050 press Test fired through S&W M&P 40 Pro 5” KKM barrel CED M2 Chronograph from a distance of 12’ in the shade under IR screens STRING ENVIRONMENTAL CONDITIONS: String 1: 82 degrees F (true ambient temperature); 30% relative humidity; approximately 5500’ elevation String 2: 56 degrees F (controlled temperature); 30% relative humidity; approximately 5500’ elevation RESULTS: String 1 @ 82 degrees F Average: 893.2 FPS SD: 9.0 PF: 160.8 String 2 @ 56 degrees F Average: 911.3 FPS SD: 6.0 PF: 164.0 ASSUMPTION: Results support statement that WST is an inverse temperature sensitive powder. Based on performance results at two known (control) temperatures, we can extrapolate the expected PF yield at any given temperature range, but keep in mind this is at an elevation of 5500’ where the air is thinner (approximately 0.0608 lbm/ft3) than at sea level (0.0745 lbm/ft3) with the same relative humidity level. Air density will affect your FPS, and ultimately, your PF. The chart below is based on 30% relative humidity at 5500 ‘. Degrees PF 105 157.97 104 158.09 103 158.22 102 158.34 101 158.46 100 158.59 99 158.71 98 158.83 97 158.96 96 159.08 95 159.20 94 159.32 93 159.45 92 159.57 91 159.69 90 159.82 89 159.94 88 160.06 87 160.19 86 160.31 85 160.43 84 160.55 83 160.68 82 160.80 Actual reading 81 160.92 80 161.05 79 161.17 78 161.29 77 161.42 76 161.54 75 161.66 74 161.78 73 161.91 72 162.03 71 162.15 70 162.28 69 162.40 68 162.52 67 162.65 66 162.77 65 162.89 64 163.01 63 163.14 62 163.26 61 163.38 60 163.51 59 163.63 58 163.75 57 163.88 56 164.00 Actual reading 55 164.12 54 164.24 53 164.37 52 164.49 51 164.61 50 164.74 49 164.86 48 164.98 47 165.11 46 165.23 45 165.35 44 165.47 43 165.60 42 165.72 41 165.84 40 165.97 39 166.09 38 166.21 37 166.34 36 166.46 35 166.58 34 166.70 33 166.83 32 166.95 31 167.07 30 167.20 29 167.32 28 167.44 27 167.56 26 167.69 25 167.81 24 167.93 23 168.06 22 168.18 21 168.30 20 168.43 Link to comment Share on other sites More sharing options...
Aircooled6racer Posted July 20, 2012 Share Posted July 20, 2012 Hello: That is some great info there I have been playing with some WST here in Albuquerque which is very dry but the elevation is close to yours. I am using 165 grain Montana Gold bullets loaded to 1.180" OAL and 5.2 grains for 90 dgree weather. It is 172PF right now. Looks like I will have to knock it down 0.2 for the winter. I really appreciate you posting this Thanks, Eric Link to comment Share on other sites More sharing options...
wide45 Posted July 20, 2012 Share Posted July 20, 2012 Are you sure the temp/velocity curve is linear? Link to comment Share on other sites More sharing options...
Derek Wallace Posted July 20, 2012 Share Posted July 20, 2012 I agree with wide45. You need more data points. Link to comment Share on other sites More sharing options...
TonyT Posted August 24, 2012 Share Posted August 24, 2012 An 18 fps difference betwen two strings does not appear to be statistically significant. Link to comment Share on other sites More sharing options...
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