Re: Remington Model 660 (6mm) Ballistics Chart???
If you want to find out the velocity for long range shooting then the best and most reliable way would be to spend $100 on a Chrony.That way you won't be just guessing.There are many factors that determine velocity, even in two guns that are alike and will thus affect point of impact down range.
The other thing you could do is:
On a calm day set out a target at 200 yards and sight the gun perfectly.Then put the target at 50 or 100 yard intervals(250,300,350) sighting in again for each distance writing down how many clicks it takes for each.Then go home and compare your actual data to a ballistic program manipulating the BC,velocity,etc until the numbers approximate each other for longer range shooting.
Steve