Originally Posted by Alan Griffith
Some good replies. Thanks.
1. Buddy called Berger. They chastised him for using G1 instead of G7 BC's. We both recomputed to G7 and it only changed dope .1 moa. What gives?
2. It was in the 70's the am they shot their rifles @ 550 yds. It was pretty windless, so probably a boil. When shooting in mirage, is the mirage going to cause one to shoot/hit high or low?
G1 vs G7 simply doesn't matter much at the distances we're talking about (as you discovered) That stuff is for the ELR guys, who are obviously in a league of their own, most of us hunters don't shoot/practice enough to have a prayer of making a cold bore shot at over 1/2 mile under field conditions most of the time. I am using G1 for the 140 VLD in a 6.5-284, confirming and re-confirming drops to 800 yds a couple times now and everything is working out just fine. Not to mention, the Exbal PC version that I am using has alot of glitches when it comes to trying to use G7's.
Mirage.............HMMM, most wont admit that it matters, except the guys that shoot benchrest competition. These guys have guns and loads that are capable (under the best conditions) of shooting 1" groups at 600 yds when everything is right. Not just the occasional fluke group but somewhat
repeatable. Ask any world class benchrester; 100-300, 600 or 1000 yd, and they'll say we never want to shoot on a boil. They'll also say that sun angle affects the image in our scopes and POI changes as the sun angle changes. Hell, a good friend of mine shoots rimfire comp and he'd much prefer an "honest" wind of 5 mph over a dead calm boiling condition. Because "we just cant predict where our vertical will end up".
As for Mirage, I am working up a custom 6.5-284 and during drop confirmation; I shot at 300 yds - 3 times - 3 different days - Once off the bench with an elevated target (both bench and target ~ 3' off the ground) and once off the bipod prone with the target 12" above the ground, and once prone off the bipod with the target elevated about 3' above the ground.
The prone position with the target just off the ground had terrible mirage. The 3" aiming dot was dancing around up to 3/4 MOA in any givin direction. The target was fuzzy no matter how I adjusted the SF knob. That group was ~2" low of where the other two groups printed under different conditions (mirage didn't appear to be nearly as bad when the target or the gun was elevated off the ground). Long story short, my non-mirage POI matched the ballistic programs, the mirage induced POI wouldn't match. I've confirmed out to 800 yds, and the mirage induced 300 yd POI was obviously a fluke. As you've said, the guns are accurate, so something has gotta explain it. Mirage is the only thing I could come up with in my experiences.
If I'd have used the mirage induce POI to tweak my velocities or SI distance, I'd never have hit this mark at 700 without further adjustments, as it was; I dialed what the program said and my errors were wind related only.