Problems with 300wsm groups

[rscott5028]

No biggie. I shot 2.5".

Come to think of it, mine was at 100yds.

congrats Matt!

 

[Peterbilt]

How much can a change in the temperature of my ammo make to my POI? I load up and go out to my bench and it may sit for 5 min or 30min depending on how long it takes to set up. Its been 15-25 outside but its 70 in my reloading room.

 

[elkaholic]

How much can a change in the temperature of my ammo make to my POI? I load up and go out to my bench and it may sit for 5 min or 30min depending on how long it takes to set up. Its been 15-25 outside but its 70 in my reloading room.

I haven't read all the previous posts but there are two ways that temp affects poi. First of all, an air temp change of 20 degrees alone will affect the poi at 1000 yards by about 4" with a .6 b.c. bullet. Add to that a temp sensitive powder that loses 50' per second with a 50 degree temp change and you lose a few more inches at 1000 yards. These things can add up in a hurry to cause major poi shifts to occur. The temp of your powder when you load has no bearing on poi. The temp of the powder at the time of ignition is what you are concerned about. Most of the long range shooters will choose a temp stable powder such as the Hodgdon extreme group to start with to minimize this variable. Leaving a round chambered in a hot barrel for a few seconds can greatly increase this problem. The bottom line is, you need to chrono your loads in different temps to see how much variation you have and factor this in along with all of the other variables which affect poi. You may never notice the difference at 100 yards but certainly will at longer ranges. Hope this helps.....Rich

 

[rscott5028]

This is a small sample size. But, it illustrates a trend that I've often heard about temperature stability being better in the Hodgdon Extreme powders than others...

I just now eyeballed some averages from my records...

Sendero 7mm Rem Mag
59.5gr RL22
98F = 2640 fps = -308" @1K
34F = 2550 fps = -331" @1k

62.4gr H4831sc
92F = 2765 fps = -277" @1K
86F = 2750 fps = -280" @1K
79F = 2740 fps = -283" @1K
34F = 2720 fps = -287" @1K

These are relatively light loads with 180g Bergers I worked up for my young son.

Again, this isn't scientific. But, it seems to hint at one reason some powders are more popular for competition than others.

-- richard