To start, I am fairly new to the ELR game. I have been load testing for my new .260 remington and found what I believed to be a good round. 39.1 grains of Varget, 123 grain nosler match bullet, out of my 1:8 twist tube was producing muzzle velocities of 2950 with as spread of +/- 5 fps. At 200 yards I was getting 0.5" groups. Great! Dialed all this into my ballistic software, found a range that let me extend its legs (550 yards to be exact, not all that extreme, but starting to get out there). This is were the problem starts. Out to 400 yards my software and mils are great. At 550 yards I should dial 29 mils. Couldn't hit the target, found out I was blasting dirt way in front of the target. Kept raising and dialing. Found my bullet to be hitting at 44 mils low. Went back to 100 yards to check my zero, right on the money. Went back and played around in the ballistics software, this would mean my bullet is going transonic at about 650 yards. Called a farmer friend and he let me shoot in his field out to 900 yards. Once again, 550 was 44 mils and anything past 600 forget it. Couldn't even see where they were going. This does not make sense to me. I am hoping to reach out and get some more opinions on what may be happening here. Also, I am heading out tonight with 30 rounds loaded with H4350 and som H4831SC to see velocities and see if they die off at 550 and beyond. Any help / suggestions would be greatly appreciated. Thanks in advance!