Hot temps and High elevation??

[6.5x300]

Got a question for the experts here..... three years ago my father drew a coveted SE Oregon antelope tag. Took the 338 edge and 300 WM for him (over gunned I know). All thought he didn't connect we saw many antelopes and he had many shots ranging from 150-600 yrds. Yes, need more practice as I am dumb founded how he missed.

Anyway my question relates to the 100 degree temp and 7000' elevation we where hunting at. If the 338 edge shoots an exact 2825fps at 1000' elevation at 60 degrees with H-1000 and Sierra 300 grain MKs how will it do at 7000' and 100 degrees and what are the potential differences in muzzle velocity and down range drop? This gun is an easy 1/4" moa out to a long ways so I still can't figure out the misses?

I entered my data in the JBM website software for the SMK at 2825fps at 7000' elv for 100 degree temps to get the drop chart and this has always been near spot on for me in the past. The one thing I don't know and suspect...... was the bullet's muzzle velocity considerably higher then 2825fps at the high elv and extreme heat?

Second question, entering the data for the SMK bullet at know 2825fps into the JBM program for the 7000' and 100 degree temp, could the info have been flawed or should I have entered it differently?

I know the reasons for a missed shot on game animals are numerous especially a small goat at long range and I accept that but I'm just really curious what your thoughts are on any potential errors I may have entered into the JBM program and if my muzzle velocity was higher at the 7000' elv and 100 temp then it was for me at a cooler and lower elv.

What have you guys experienced in the difference in muzzle velocities at different/extreme elv and temps?

Thanks

BT

 

[theEMP]

At higher elevations the bullet will not loose as much speed over distance due to thiner air. I don't know what it will do at the muzzle but at long range there will be a point of impact shift due to more retained velositly. Maybe there is enough change to explain the misses?

 

[6.5x300]

Yep, I agree with that. I would have figured though that entering 7000' and 100 degrees into the JBM calculations would have taken that into account though.

 

[EXPRESS]

In a cartridge like the .338 Edge, at 150, there isn't going to be any real world difference, while at 600, there could be up to 10 inches less drop compared to your home range zero for the kind of differences you are describing.

Did he check zero once he got to the new hunting area?

 

[theEMP]

That was my next thought as well. If the zero wasn't corrected it would cause problems

 

[6.5x300]

yep! zero was off by nearly 2" at 100, we found that out a couple days into hunt, certainly accounted for a couple misses, don't know why or how lost zero, had a SIII scope that had never given problem or problems since. what gets me is after perfectly resetting zero, couple days later had a perfect broad side shot at ranged 500yrds center mass hold and still missed? Dialed up for holds according to JBM calculations of 7000' and 100 degrees.

 

[Rogue Hunter]

Scopes do fail...
Have you since checked the tracking of the scope to see if it's returning to zero, and moving the value that you are inputting into it? Shooting and adjusting it on a grid at 100 yards might reveal something.
Higher temps will increase chamber pressure and velocity. Elevation changes the air density (higher = less) and drag forces that the bullet has to overcome. JBM is typically very accurate when the correct info has been input.
When I did my Oregon lope hunt in 2011, I saw very little difference in my drops while shooting my .257 Wby. It was zeroed at 300 yards at 1100 ft elevation and 85 degree temps here at home. We were hunting at 5000 ft. with 90 degree temps. Shot my buck at 298 yards (how convenient right?) and drilled him within an inch of my aiming point.
I would be suspect of the optics, or the human factor behind the gun.

Regards,
-Mike