Hi mountain cur,
Any time you increase the magnification of a scope, it will change the point of impact for a crossbow or a vertical bow. This is because either one is not actually shooting flat, in the same way a bullet would.
What I have done to compensate for this is to create a sight tape that I attach to my crossbow stock. The tape simply lists all distances from 20 - 120 yards in 5 yard increments in the left hand column. Next column list my scopes magnification setting at each distance. My last column lists the actual setting I use on my HHA Optimizer Speed Dial. I increase my magnification power beginning at 70 yards and again at 90 and 110 yards. As long as I always use the same magnification setting at these distances, my point of impact remains consistent, therefore my HHA Optimizer Speed Dial Setting is dead on.
You also need to be aware of slight elevation changes which will always be due to temperature changes. Temperature changes alter the density of air, so the hotter it is the thinner air becomes. This causes your arrows to fly higher at longer distances. As air temps cool off and drop, air becomes thicker and causes arrows to drop faster.
I have site tapes which I recorded at different temperatures, so as air temps change as seasons progress, I can easily remain dialed in when shooting longer distances.
I don't think you'll much written about this in to many places, but you can easily test it and validate it for yourself. Most competitive archers have know this for many years and automatically adjust for the temperature changes while at the practice butts on the morning of any important shoots.
Regards,
Jon Henry
