Muzzle velocity significantly dropping

[Bob Nelson 35Whelen]

Hello gentlemen,

Hope you’re all doing well and safe! So, we were hunting ibex in Tajikistan last week, and we had to use the outfitter’s rifle:
Rifle Brand: Ruger Hawkeye (Twist rate: 1 in 9.5)
Caliber: 7mm Remington Magnum
Bullet: Nosler Accubond 160 Grain (Trophy Grade)

While checking the rifle on the first day, I decided to chronograph the loads and get the average muzzle velocity using my Magneto Speed (Temperature was 28 degrees F). I know the velocity can drop in colder temperatures, especially when using unstable powder. However, this one was significantly dropping even between 1st, 2nd, and 3rd shots! I’m attaching a picture of the chronograph results.

1st shot was 987m/s
2nd shot 869m/s
3rd shot 784m/s

Has this happened with any of you before? What would you do in such a case? Knowing it’s very common to shoot at 400-600 yards in this hunting area (A 200 m/s OR a 656.168 ft/s difference will greatly affect the point of impact at such distances). Your help and experience would be highly appreciated!

View attachment 380037

@youssefchagoury
Reading the instructions on the Magneto Chrony you apparently need a different battery for cold weather opperation. I don't know if this is correct or not but could be so.
Bob

 

[youssefchagoury]

Sometimes you could get lucky, and be able to close the distance to what you're comfortable with... But most of the time you don't have that luxury in such mountains. These hunts can put any hunter out of their comfort zone!