Velocity in cold weather

45308

45308

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I have been reloading and Chrono graphing loads for several years now, but I have never done cold weather vs warm weather verifications. Here is my scenario..... I have a Magnetospeed chronograph as most of you probably know, mounts to the end of the barrel. I checked the velocity on a load the other day at -20 deg. C. and I had the ammo stored in my warm vehicle until I chambered the round. (I figure the powder should have been somewhere between 15 and 25 deg.). We certainly know that cold ammo will have lower velocities but what about the air temperature itself? Cold winter air can have a higher barometric pressure but that is obviously not an issue when the velocity is measured off the end of the barrel. So, my question is this, if my ammo was warm and I measured the bullet speed at the barrel, could the outside air temperature (-20 deg.) possibly effect my velocity reading? Would the cold temperature of the gun itself effect velocity?

thanks
 
No. Your test is a warm powder test.

If I have a lot of ammo testing to do in the winter and I have to shoot outside, I take the ammo to the range in a picnic cooler. In the cooler is a pair of 2 liter pop bottles filled with hot tap water. This keeps the ammo toasty.

When it comes to me to shoot, I put the 5 rounds in my shirt pocket. And then load and shoot one at a time. This keeps the ammo around 98F. This way all tests results are comparable.
 
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If all other factors are held constant, cold air will be denser than warm air. Denser air will tend to slow the bullet more over the course of its trajectory. However, you aren't going to see that affect at the muzzle.

Other factors that affect air density (and therefore trajectory) include altitude (less density with higher altitude) and humidity (counterintuitive though it may be, humid air is less dense than dry air).

Of course, these factors can interact. Over the course of one winter a few years back I decided to measure how much effect I would see from changes in temperature. This is a crude test, but it gave me a number I could use for hunting when 30C swings in temperature are totally possible over the course of a season.

I used my 30-06 and a load that gets, on average, 0.9 MOA in my rifle. 6 times over the course of the winter I would fire two shots at identical targets at my range. I always fired at 200 yards. I always used the same point of aim. I always fired the shots from a clean dry barrel. I tried to pick days across a range of temperatures (wound up with -25 to +15) I determined the mid-point between the bullet holes and measured the vertical (only vertical) distance between the point of aim and the mid-point.

The result was surprisingly linear (R2 = 0.94 for those who care) for such a crude setup. I found that for every 10C drop in temperature, I would get about a 0.66 MOA drop in point of impact (again, measured by the mid-point method).

I couldn't isolate effects from humidity vs. temperature, I couldn't account for headwinds and tailwinds, nor minor changes in muzzle velocity, but the aggregate effect is still interesting.

My load was a 165 gn Hornady SST over 59 grains of H4350 (one of the hodgdon extreme powders which should minimize the effect of muzzle velocity) which chrono's at 2925 fps at 23C

I think cold temperature should constrict the bore of the rifle very slightly. At the same time, it should also shrink the calibre of the bullet very slightly. Whether or not this has any net effect on muzzle velocity probably depends on bullet and barrel construction methods and materials.

Fat
 
I did some experimenting with W760 in warm and cold weather.
The load was in a 30-06, and was as follows:
Winchester case; Nosler 165 grain Partition; CCI 250 Primer; 60 grains of W760. COL - 3.345"
At 22ºC, this load graphed 2990 fps average for 5 shots. [24" barrel]
At -30ºC, this same load graphed 2702 fps average for 5 shots...a fair difference.
Interestingly, the point of impact dropped down 1½" and moved 1" to the right at 100 yards.

A more recent experiment was done with the same rifle, but using the 180 Partition and Norma MRP
Winchester case, 180 Partition, Remington 9½M primer, 61 grains of Norma MRP, COL - 3.345"
At 20ºC, this load graphs 2855 fps average for 5 shots
At -20ºC [not quite as cold] the same load graphs 2829 fps average for 5 shots. This surprised me a bit,
since MRP is a double-base powder, and I expected it to be affected more. The POI stayed essentially
identical.

It is always a good idea to test POI of "cold" ammo, if the load was developed in warm conditions. Otherwise,
keep the ammo warm. :) Eagleye.
 
A few years ago I needed to develope some loads for a 30-06, and send the data to a custom powder in Australia who would put up 1000 in new brass for me. They had to be with powder readily available there, which pretty much left me with Hodgdons which is made by Australia Defense Industries. My own load for that gun was 4064 with 165-8s.

Trouble was; we were in a cold snap with mostly forty below.i could get the Cooper shooting, but I don't remember a single load that broke 2700 fps at that temp and some
didnt make 2600. Remember, this was with 165s. Varget was the fastest of
the bunch.

At -20C it started to wake up, and by zero it wasn't far off the 2950 fps that the dial is cut for.
 
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7mm SAUM 150gr Nosler BT
IMR 7828ssc
+17c ~ 3087 fps
-14c ~ 3026 fps
1.97fps per degree Celsius

260 Rem 127gr Barnes LRX
RL17
+12c ~ 2938 fps
-16c ~ 2893 fps
1.61fps per degree

300 Win Mag 200gr Nosler AB
H4831sc
+20c ~ 2799 fps
-3c ~ 2767 fps
1.39fps per degree

300 Win Mag 210gr Nosler ABLR
RL26
+22c ~ 2809 fps
-16c ~ 2712 fps
2.26 fps per degree

308 Win 208gr Hornady ELD-M
Varget
+25c ~ 2225 fps
-1c ~ 2195 fps
1.15 fps per degree

223 Rem 40gr Hornady Vmax
RL10x
+14c ~ 3427 fps
-14c ~ 3396 fps
1.11 fps per degree

300 WSM 200gr Nosler AB
RL26
+26c ~ 2895 fps (21 round avg)
-16c ~ 2890 fps (14 round avg)
0.12fps per degree.
 
some more results

7mm SAUM 162gr Hornady ELD-X
RL26
+15c 2970 fps
-5c 2969 fps
.05 fps per degree

260 Rem 129gr Nosler ABLR
H4350
+16c 2780 fps
-2c 2773 fps
0.39 fps per degree

300 Win Mag 175gr Barnes LRX
RL26
+22c 3125 fps
-4c 3116 fps
0.35 fps per degree

338-06 210gr Barnes TTSX
CFE223
+23c 2778 fps
-5c 2694 fps
3fps per degree

375 Ruger 300gr Nosler Partition
Win 760
+23c 2580 fps
-5c 2512 fps
2.4fps per degree
 
not all Alliant RL powders react the same.I hear RL22 is bad, I haven't used that powder myself for a long time, but just got some so will be recording results as they come. cheers
 
I am surprised and confused by the above results.
TB's result fly in the face of much we hear. Velocities don't seem to be too far off in fact they seem normal reductions in the cold if I can say that.
Others don't seem to do so well in different calibers, Trying to make sense of it all.
There is a lot of bad mouthing when we talk about temperature sensitive powders but these look pretty D. good venture to say excellent.
BB
 
bigbull said:
I am surprised and confused by the above results.
TB's result fly in the face of much we hear. Velocities don't seem to be too far off in fact they seem normal reductions in the cold if I can say that.
Others don't seem to do so well in different calibers, Trying to make sense of it all.
There is a lot of bad mouthing when we talk about temperature sensitive powders but these look pretty D. good venture to say excellent.
BB
Click to expand...

Part of it is his test temperatures just aren't that cold. I'd love to see someone get results that good at 30-40 below; I'd be lining up to buy it. Unfortunately the manufacturers aren't yet claiming to get what I want.
 
To the right of the powder type below is a number that represents the fps change for each degree of temperature increase/decrease.

As a example the American 7.62 sniper ammo was changed from RL15 (1.52) to IMR-4064 (0.45) due to the temp extremes in Afghanistan and Iraq.

Also you can see that double base powders are more sensitive to temp change, and the Australian/Hodgdon extreme powders the least sensitive like Varget at (0.13).

33XPgx3.jpg
 
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