This is presented for entertainment only. Your results will vary.
I spoke with a gentleman at Accurate Arms yesterday about ambient temperature effects on maximum chamber pressures and velocities. I say “ambient temperature” but am not just implying air temperature, but firearm/cartridge temperature as well.
I think his name was Ted. He didn’t have any information on chamber pressures, but had done some work with Speer back in the 70’s and hence pulled out a Speer manual (#17???) and read some numbers off for me. He didn’t tell me what the firearm/caliber was (I suspect it was a military round), but gave me this information:
0F 2630fps
70F 2722fps
100F 2827fps
Then I rummaged around the garage last night and found a “Reloading Guide for Rifles and Handguns” from Vihta Vuori Oy, noted 1-97. This was one of those freebie-types you pick up at the gunshop in amongst all the reloading supplies. This manual had a little more specific information:
For 9mm Luger, 5.56grs of N330, 115grFMJ:
-65F 14200 psi 1046fps
70F 25900 psi 1233fps
126F 27700 psi 1249fps
For .308 Win, 45grs of N135, 147grFMJ:
-67F 38000psi 2542fps
70F 50900psi 2742fps
140F 55200psi 2808fps
This manual provides a small table of Interior Ballistic Variables, one item being Powder Temperature. It notes a good quick rule of thumb is the relationship for a +50F change in powder temp, add 2% to velocity and add 4% to maximum chamber pressure.
So I plotted some of this information up to see what it looked like. I found the +2%velocity for +50F rule to be fairly representative, but not the +4% in Pmax-- the data reflects a steeper slope, more on the order of +6% to +8%.
I noted earlier reference to a table of Interior Ballistic Variables:
Bullet weight +10% ....–4% velocity……….+8%Pmax
Charge weight +10% …….. +8% velocity …….+20% Pmax
Power temp +50F ………… +2% velocity ………. +4% Pmax
Cartridge case volume +10% ………..-7% velocity ……… -40% Pmax
While changes due to ambient temperature don’t appear as extreme as the other variables listed, these other variables are controlled at the loading bench. Weather conditions, obviously, are not controlled, BUT… if you have worked up to a maximum load under mild weather conditions, leaving ammunition in the sun during a hot summer day could create overpressure problems.
Worth noting.
I spoke with a gentleman at Accurate Arms yesterday about ambient temperature effects on maximum chamber pressures and velocities. I say “ambient temperature” but am not just implying air temperature, but firearm/cartridge temperature as well.
I think his name was Ted. He didn’t have any information on chamber pressures, but had done some work with Speer back in the 70’s and hence pulled out a Speer manual (#17???) and read some numbers off for me. He didn’t tell me what the firearm/caliber was (I suspect it was a military round), but gave me this information:
0F 2630fps
70F 2722fps
100F 2827fps
Then I rummaged around the garage last night and found a “Reloading Guide for Rifles and Handguns” from Vihta Vuori Oy, noted 1-97. This was one of those freebie-types you pick up at the gunshop in amongst all the reloading supplies. This manual had a little more specific information:
For 9mm Luger, 5.56grs of N330, 115grFMJ:
-65F 14200 psi 1046fps
70F 25900 psi 1233fps
126F 27700 psi 1249fps
For .308 Win, 45grs of N135, 147grFMJ:
-67F 38000psi 2542fps
70F 50900psi 2742fps
140F 55200psi 2808fps
This manual provides a small table of Interior Ballistic Variables, one item being Powder Temperature. It notes a good quick rule of thumb is the relationship for a +50F change in powder temp, add 2% to velocity and add 4% to maximum chamber pressure.
So I plotted some of this information up to see what it looked like. I found the +2%velocity for +50F rule to be fairly representative, but not the +4% in Pmax-- the data reflects a steeper slope, more on the order of +6% to +8%.
I noted earlier reference to a table of Interior Ballistic Variables:
Bullet weight +10% ....–4% velocity……….+8%Pmax
Charge weight +10% …….. +8% velocity …….+20% Pmax
Power temp +50F ………… +2% velocity ………. +4% Pmax
Cartridge case volume +10% ………..-7% velocity ……… -40% Pmax
While changes due to ambient temperature don’t appear as extreme as the other variables listed, these other variables are controlled at the loading bench. Weather conditions, obviously, are not controlled, BUT… if you have worked up to a maximum load under mild weather conditions, leaving ammunition in the sun during a hot summer day could create overpressure problems.
Worth noting.