Anywhere from 1.28X" to 1.3XX", sometimes within the same box.
I'm done some testing along with a few other F-Class guys in my club. Every one of us had different average lengths. I haven't measured BTO yet though.
I talked to a competitor this weekend who uses the new 110g SMKs in his 6mm and he ran into the same sporadic lengths, so he switched back to 107g SMKs.