When pulling an average velocity reading from your chronograph and taking that velocity to input into what ever ballistic app you're using, do you add a skootch more to make up the loss of speed from the muzzle to the chronograph? Someone once told me to add about 30 fps so that if my chronograph reads 2750 fps I should input 2780 fps in my ballistic program. This when the front screen of my 35P is 10' from the muzzle. Just this morning, shooting at 950 yds with a 140 Hybrid from my 6.5x47 I was impacting several inches low. This rifle/load is currently placing 5 into less than 1/4 to 1/2 moa at that range so I'm pretty sure of the drop/impact distances.
Alan
Alan
. When I used to use a Shooting Chrony at 10' from the muzzle, I would add a few fps back to the Avg MV value. If you want to get as rough estimate of how much to add for a given load, just run the avg MV through JBM Ballistics with the atmospheric and load specs, setting the maximum range to 10 yd, with the range increment set to 1 yd. The approximate decrease in velocity for the distance from the muzzle to chronograph can be estimated from the velocity column; in this case about 7 fps for a 10' distance. You probably won't notice much of a difference at close range, but it might be worth doing if you're shooting something like a .308 with a fairly slow MV out to 1000 yd. Even then, the difference shouldn't be huge (< 0.5 MOA)
