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Velocity change with temperature change; BH209

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GSSP

Member
Joined
Nov 30, 2019
Messages
8
Dilema.....
Heading out on a cow/spike elk hunt Wednesday. Morning temps will be freezing or lower increasing into the low 60's, depending on the elevation i'm at. Last week I was checking my dope out to 600 yds. It's spot on! Temp was around 60 F. Average mz velocity was 2525 fps. I waited until today to check my velocities in 30 F temps as our first snow storm of the year is upon us. I FULLY expected lower velocities. Instead my average was 2567 fps for 14 shots; 42 fps faster. I tweaked my 200 yd zero while I was at it. I think these 3 shots give me the confidence I have a solid 200 yd zero.
Any input on the velocities "increasing" in colder temps with BH209 (122 gr by weight)? Bullet is the Parker 300 gr Black Max. Rifle is one of
Levi Reed
's UML conversions. Thank
Levi
for building me such an awesome rifle!!!
 

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tpcollins

Well-Known Member
Joined
Mar 4, 2007
Messages
853
Barrel shrinkage causing increased pressure?

Colder barrel creates more friction than warmer barrel?

Since colder air is more dense, I would expect the velocity would be less at 200 yards poi versus warmer air.
 

GSSP

Member
Joined
Nov 30, 2019
Messages
8
I talked to our Ballistics Engineer at work today. He had two possible opinions. 1. Changing lot # might be a definite cause; different hardness in the core lead or a different thickness in the Black Max jacket. 2. The first lot had been sized via the Swinglock sizing die in warmer (60-70 F) temps vs the 2nd lot were being sized yesterday, at the range, in 30 F temps. Maybe more springback or resistance to sizing? I'll check my velocity and 600 dope one more time with 2nd lot # bullets, sized in room temp bullets.
 

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