Another question about temp and powder performance

[phutch30]

I am haveing a custom bullet drop comp made for my rifle scope and one of the parameters they factor in is temp. My problem is I will have a 50-70 degree temp difference between now, which is when I am generating velocities to submit and this fall when I will be hunting. My first question is this:

How much velocity difference could I expect in a 63gr load of IMR 4831 between the current temps which are in the 90's and hunting temps of 0 to 30 degrees. Current velocity is 3044. Is it likely to be more or less then 30-40 fps? After 40 it will begin to have fairly significant effects on bullet drop past 550 yards.

Second question:
If I place my bullets in the fridg and then into a cooler to chill them down to 30 degrees or so, would this be a sufficent to replicate fall/winter/field conditions if I remove them 1 at a time and shoot them quickly through the croni. Would there be any safty issues to consider?

I realize these questions may seem a little off the wall. Take into account I dont plan to shoot past 500 yards while hunting, but dont want to spend the money unless I get my monies worth. Plus I would like to practice out as far as the BDC is calibrated, which will be 850. So a 30-40 fps difference could be frustrating on the range at long distance.

Thanks

 

[steve4102]

Cooling the bullet in the fridge is only half of the equation. You need to cool the rifle and barrel as well for your test to be valid.

 

[Ol` Joe]

I read somewhere to figure 2 fps/degree F reduction in velocity. I did a check on R22 and temp variation useing my RSI Pressure Trace and Pact M1 crony. The result suprised me, almost no velocity loss for the pressure drop. I posted the results here if you are interested. http://www.24hourcampfire.com/ubbthread ... ost1460421

I don`t know how IMR powders would react, they may or may not be affected like the Alliant R22 was. The best you can do is crongraph your load at both the normal high and low temps you expect to shoot at and see for yourself. The rifle does, as noted by Steve, need to be at ambiant temp along with the ammo to get a honest reading.
I doubt out to 300 yds you will notice any difference on game, at longer ranges you will find some change in drop. How often do you plan on shooting game at ranges over 250-300?. I doubt you`ll need to take these shots often, if at all, under most hunting conditions.

 

[JD338]

phutch30,

In all honesty, within 500 yds, the temp range will have a minimul effect
on the bullets point of impact. The same is also true with elevation.
Take a look at the link to the attached ballistics calculator and play with the variables of temp and altitude.
http://www.biggameinfo.com/BalCalcAdv.aspx
There really isn't enough to worry about. :wink:

JD338

 

[R Flowers]

I did a similar test with my 25-06 last fall and was surprised how much velocity IMR 4831 lost when shot in cold conditions.

I loaded up some ammo then put half of it in the freezer for a few hours. I then put it in an ice chest and hauled ass to the range. I shot ammo that was at ambient temperature and then shot the same loads from the ice chest. I actually did this on two different days just to make sure one day of testing was not a fluke.

On the first day the loads using IMR 4831 lost 68 fps when shot cold and on the second day the IMR 4831 loads lost 65 fps. (When compared to the same loads stored and shot at ambient temperature of maybe 70 degress.)

The first day I also tested H 4350 which actually gained 43 fps when shot cold. I also shot H 4831SC which gained 23 fps when shot cold. This is the third gun that I have tested H 4831 in and found it to shoot faster when shot cold, right out of an ice chest.

On the second day I shot RL 22 and it lost 34 fps when shot cold.

Now these were only three shot strings and were statistically insignificant. However, the fact that IMR 4831 lost nearly 70 fps on two different tests tells me there is a problem with that powder in cold weather.

Can I shoot well enough to tell the difference? Probably not, but it is interesting.