Question for you. Is there a way to accurately determine wind so I know how much to hold off/dial? Also, with air temp, can I average the temp so I can get my dope, considering I may not have a long time to calculate with the exact temp on an animal? Thank you!
Well this turned into a long answer. Sorry for the wall-o-text.
The term "accurate" is relative. Learning to read wind mirage and the swaying of trees/shrubs/grasses is going to be your best bet for field expedient accurate wind calls and it's also the hardest thing to get proficient at. It truly is an art as much as a science.
Air temperature is going to matter in terms of 20F increments for drops, not 5F and with a 7RM and any of those loads it will matter in terms of 1 click (.25MOA or .1MRAD) with the loads above to something well over 1000 yards. You'll need a 40F difference to matter 1 click of drop at 600 yards with the loads above. It's something to be aware of but not to get preoccupied over.
Wind is another matter entirely. It has a velocity component and a direction and both of those will be affected by terrain. Speed of wind is also variable based on the height of the projectile above the ground (winds can be nearly non existent a few inches from the ground yet quite pronounced just a couple meters up). Since long range shooting involves trajectories that can put the bullet potentially substantially above the line of sight it's important to know how far above LOS it'll go and how much of its flight will be there and to keep that in your head for the wind call. All that said, 600 yards with a 7mag is darned near a chip shot. Something around 2.5mils of up and 1 mil of over in a full value 10mph wind. You can nearly hold on-hair on a large deer without adjusting and still make that hit... nearly. To ~400 yards, you can just about get away with holding "on hair" with a 7mag and just adjust for wind.
To break that out into familiar terms of linear measures: Using a 7mag with any of the loads above, a full value 10mph wind at 600 yards is going to make for about 18 inches (3MOA) of drift. 10mph is not a small wind. Down around 3-5mph the difference is closer to 10 inches of drift. It's when it gets stronger than about 15mph that it gets very hard to estimate (trees only sway so much, mirage becomes less helpful) and the drift at 15mph is something near 30 inches which could amount to a cruel wound or a clean miss real easy. Above 15mph you're best off not taking the shot IMHO. Wind meters like those from Kestrel and Caldwell and such only tell you what's going on where you are but in the real world, unless you're hunting somewhere shaped like a table top your reading will be affected by land forms, vegetation, sampling elevation, etc...
Once you've got the wind velocity, then you need to find the wind angle relative to the shot, find the angle cosine for that and multiply that by your indicated wind adjustment. I find it a lot easier to bracket the wind but that also requires me to keep my shot distances pretty short by my standards and I don't like to take shots at game in winds over 15mph. I get nervous when I do.
A wind call example that might give perspective: My last shot on game that had any wind worth mentioning was a 150gn GameKing from a .308win on a 220+ yard shot in a heavy wind. It was taken over very short scrub brush at a springbok (an African antelope about the size of a large dog or very small blacktail deer). I couldn't get a good read on vegetation sway but it was howlin' so I guessed that it was >20mph. The wind was so severe that had the buck been any further away and I wouldn't have taken the shot. He was head down with his nose at the same elevation as his shoulder so I held the crosshair on his nose and hit the loud switch. The bullet hit the heart square in the middle. Total wind drift was something very close to 12 inches, which verified my wind call as much as my wind DOPE. That's experience + skills and I was still a little iffy on taking the shot in those conditions but after 23 hours on airplanes to get there I wasn't keen on passing up much.
I do offer products and associated services for creating nearly indestructible DOPE cards that are meant for field use cases where one shot is all you get that takes care of most of the figuring for you and they are easy to use when you can't think straight. If you'd like to discuss those things specifically, PM me.
