I would also agree that your probably having some stability problems as your bullet drops out of supersonic velocities.
This can be hell on accuracy for most bullets in fact.
If your loads are shooting well at 1000 yards but not at 1760, you are having something happen to the bullets stability somewhere in between.
IF you have access to ground where you can do this, I would recommend shooting at 1250 and 1500 to get an idea where your problem is happening at.
While the 6.5mm is a hell of a 1000 yard caliber, there is a reason the big dogs are used at the mile mark.
I have not tested my Kahn out at extreme range yet but the ballistic models say it will stay supersonic at my altitude out to 2250-2300 yards with the 300 gr Wildcat ULD.
I have shot the 50 BMG out to 2300 yards usingthe 750 gr A-Max loaded to 2750 fps and it has performed well. We have a rock that we are trying to turn into gravel and once dialed in and the wind is doped correctly, the big 50 will hammer this rock which is about 7 feet in diameter with suprizing regularity if a good pilot is onthe rifle.
My personal feelings are that shooting groups at 1000 yards is very difficult to do with the proper equipment, for evey 100 yards past that, I would say the difficulty of holding consistant, tight groups multiplies by 10!!
Many feel that since they are shooting good groups at 1000 yards, stretching it another 760 yards should not be that big of a deal. Us that have tried it know the opposite is the trueth.
There is nothing like dropping a piece of lead on target at a mile though. Nice thing about the 50 when that big 750 gr A-Max lands, the dust cloud is extremely easy to see, sometimes with the naked eye and the report drifting back over that mile and a quarter is the most beautiful sound. Hearing a solid smack at 2300 yards come back to you makes you realize the power of the 50.
The 338's are nearly identical in ballistic Performance withthe larger 338's and the ULD class bullets but nothing compared to the terminal performance of the BMG, well, nothing I have shoulder fired yet!!!
If you want to play with the mile range, you may need a little more bullet and a little more horsepower for consistant results.
Shawns comments on velocity spreads are right on the money. I though my initial 50 BMG loads had a good E.S. with 25 fps. At +2000 yards, you would miss a house. After some extensive tinkering I was able to get spreads in the single digits and this greatly controled group spreads. Even a 10 fps spread will result in a dramatic difference in impact location. This is what makes extreme range shooting so difficult.
We are basically unable to produce ammo that is perfectly consistant enough for in velocity for really tight groups. I would say 80% of my group variation at 2300 yards is vertical unless I am having a bad day or its breezy. Get a little shaky if I don't eat breakfast before a day of shooting, not a pretty sight at 2300 yards.
IF we could get velocity spreads into the threoretical 0 range, this would greatly reduce group sizes. This is impossible though so we do the best we can.
Good Shooting!!
Kirby Allen(50)
