Effects of Temperature on Velocity and Pressure

Velocity and pressure are both measurably affected by temperature.

The following chart was worked out by the famous big game hunter, Les Bowman, of Cody, Wyoming. Les has the following to say about this effect:

"Few handloaders realize the difference temperature of powder makes in velocity and pressure. And the funny thing is that the top temperatures, that is from 72 degrees normal to 100 degrees for instance, affects pressure more than from 70 degrees down to zero. As you will notice in the chart, there is a 129 fps minus for the zero temperature reading at 4000 fps bullet speed, and 155 fps plus for the temperature about 70 to 100. Many sight in one day when it is a certain temperature and later, when temperatures are perhaps 50 degrees different, they think their scope has changed when groups print at a different place. Also maximum loads worked up at, say 40 degrees, can be really dangerous at 90 or 100 degrees. It's the powder temperature that counts, not the temperature of the outside air. I have had a lot of correspondence with DuPont and was told by them that they figure 60 p.s.i. in pressure difference for every degree in powder temperature change. In the case of the 4,000 fps above at 155 on the high side and 129 on the low, or a difference total of 284 fps, that would make 17,000 pounds difference in pressure. This is the correction chart I use, and while I do not claim it is absolutely right, it is close."

Temperature Correction Chart Used by Les Bowman

Add This To Tested Velocity Tested Temp Subtract This From Tested Velocity
100'F
90'F
80'F
70'F
60'F
50'F
40'F
30'F
20'F
10'F
0'F
85
56
24
2300
18
36
50
54
57
66
80
90
58
25
2400
19
37
50
56
60
70
84
96
60
26
2500
20
38
51
58
65
77
88
101
62
27
2600
21
39
52
60
69
89
89
105
64
28
2700
22
40
54
62
71
81
90
108
65
28
2800
23
41
56
68
77
85
91
112
66
29
2900
24
43
58
70
78
88
94
116
68
30
3000
25
44
60
73
83
91
97
121
71
32
3100
25
45
61
74
85
93
98
124
73
32
3200
26
47
63
77
92
96
102
126
75
33
3300
27
48
66
82
94
101
106
132
77
34
3400
28
50
68
82
94
102
110
135
79
35
3500
29
52
70
85
86
106
113
140
82
37
3600
29
52
71
86
98
108
115
144
86
38
3700
30
54
73
89
101
111
119
147
87
39
3800
31
56
74
91
104
114
123
151
89
39
3900
33
57
78
94
107
118
126
155
91
40
4000
33
59
80
97
110
121
129

Copyright 1998-2014 Stephen Ricciardelli