I ran my .264 140 grain loads through the chrony earlier this summer and got 3300 fps at around 80 - 85 degrees. I ran them through again last weekend at 23 - 25 degrees and got 3100 fps. A difference of 200 fps seems a bit high, doesn't it? I'm concluding that the 3300 fps was the erroneous reading.

Don't count on a mistake on the first reading. I chronographed at 70 degrees at home and then below freezing at 8000' and that's about the difference I noted in a 338 Win Mag, 225g bullet over an Oehler 35P.

At tje muzzle the elevation change wouldn't have anything to do with it. It's all temperature there.

In the latest Rifleman Boddington says the velocity varies 25 fps with every 10 degrees F.

All the more reason to winter in Florida.

Some powders are quite stable but some do vary a great deal with temperatures.200 fps is quite believeable in this case.

I rccently saw a test where all the stick powders dropped a quite a bit---then came the BIG SURPRISE. A load with win 760 actually got more potent as it got colder. If I remember the guy was comparing loads at 70 degrees to loads he had in a cooler that had been prepped just below zero.
Myabe it had something to do with concensation or something affecting the coating--can't explain it and neither could the tester.

I've read some stories of polar bear hunts where the temmps were extremely low and the authors saying the guns even had different sounding reports when fired as compared to normal shooting temps.

Temp can have an effect. I was chronoing some handgun loads and was putting in more powder (1 and 1.5 grains more) and I was getting less velocity than with the lower loads. It was about a 20 degree difference. I don't have the figures with me but I thought I did something wrong.

The heat does have an effect with most powders. The other variable is it the same powder lot? That can change things also. That is why you are supposed to chron max loads in the heat of the summer. If going to a warm climate you should try to chrono at similar temps.

Hcliff

It can be cold outside, but be a very hot day in the chamber.

Shooting a round every 30 seconds gets my barrel so hot I can't hold it.

Put a round in that chamber and wait a couple minutes and the powder thinks it is on the asphalt in Iraq.

I've fired rifles while hunting in sub-zero temperatures, and if it's cold enough you can hear the differance when the gun goes off. Some of the new powders aren't as sensitive to temperature changes, but in temperatures that are reasonable, I'm not sure the differance would be worth the trouble. A 200 fps change from temperature doesn't surprise me though. I try to chrono' all my loads in the cold as well as summer temps, just to check this variation. (Monday morning; minus 21, brrr) - Dan

This is kind of an eye opener and a good test to to perform.
Once you have a load worked up that suits you, take a half dozen or so and put them in the freezer over night and take them out to the range in an ice chest and fire them the next day. As I have found you may find a decrease in velocity between 75 to 150fps average depending on powders used. The slow extruded powders tend to be harder to ignite, I've even had some hang-fires, and have since gone to Winchester WLRP primers (To my understanding are the hottest) to help keep this from happening. FYI, I had a good quality thermometer in the ice chest and it read 25 degrees when I took the rounds out to fire them at the range. The reverse will happen on very hot days also a load worked up and fired on a cool day, pressures will spike up appreciatively on a very hot day.

It is a problem with most powders I've found. Anywhere from 50-200 fps is normal. I read the artical about the spike in win760 too.

If you shoot at longer ranges this is critical as well as the change in density that a ballistic program will predict fairly close. The MV because of ammo temp is up to you to determine with the change though. 20-25 fps every 10 deg is real close to what I've found so far.

Temperature definetely makes a big difference especially with our sensitive powder in RSA.
My one friend who shoots sillouette with his custom 6.5 he takes a themometer when he goes to the range to see where the bullets end up on the targets at 300 meters with diffrent temp. writing all this info down to use at competitions.

I was surprized when he told me what changes the temperatures can make. I saw it for myself when I developed a load for my 375 with a 210 grain barnes on a hot day 32 degrees Celcius I got 2950 fps and on a cooler day 28 degrees celcius 2850 fps that si 100 fps difference. So I don't know how fast my load was going in the eastern Cape where I used this load and it was mighty cold 10 degrees celcius.

I also think that the higher the temp the higher the presurre tends to push up as well. And that is why poeple who go after DG in Africa have problems extracting their cases from hot loads on hot days in the heat which can still climb to temp over 100 F in winter at some places.

Yesterday, Thanksgiving, did some shooting with a 7x57, using H4350, W760 and RL-19. The loads tested were one grain more than the initial loads I'd tried earlier. Temperature at time of testing the original loads was 45 degrees F; yesterday, it was 22 degrees F. Of the three powders tested, the only one that showed an increase in velocity was H4350.

W760 and R19 gave LOWER velocity readings, with one grain more powder. H4350's increase was pretty much what you'd expect (original load was 49 grains, with 150 grain Power Point, and 2,670 FPS average; this load was 50 grains and produced 2,730 FPS average), so, maybe Hodgdon's got something there with their "extreme" stuff, at least in the case of H4350.

Still scratching the old noggin over the W760 thing, tho.. My lot is pretty old (cans are marked "MidSouth, 1-89"), so, maybe the increase the guy got in that article is due to his lot being different or something.

R-WEST

[ 11-29-2002, 18:17: Message edited by: R-WEST ]

The W760 increase was kind of strange.

Try this test next time you go to the range. Take along a cooler with a couple of bags of ice & a tupper ware container with the lid that your wife is going to let you borrow. Before you head out to the range put 5 of your rounds into the tupper ware container with the lid nice & tight & put it in the cooler full of ice. You get to the range, shoot a group with your uncooled ammo. Now shoot for a group at the same target with the cold stuff & watch what hsappens. This probably is a waste of time for you guys in the Northern climites.