I’ve had a strange occurrence lately that I cannot explain. I bought a rifle from an estate sale. It was a custom 6.5x47 lapua and it came with loaded ammo. The loads stated 120gr amax with re15. I sighted the rifle in and the loads shot great. I didn’t have my chronograph that day so I guessed the velocity at 2900 and plugged it into my Applied Ballistics phone app. To my surprise my drops were dead on! I took the rifle hunting and killed 6 deer from 200 all the way to 980 with the load and ballistic data. Fast forward a couple months. I’m running out of loads from the previous owner so I load up some identical loads, assuming his data was correctly annotated. I take those new loads and the old ones to shoot side by side. To see if I can replicate the accuracy I had previously seen. To my surprise the Oehler 35 read an average velocity of only 2745fps. What is going on? How are my drops on with a velocity of 2900 but my bullet is only going 2745?