COL is 2.54 (based on the Sierra manual)
I'm going against my own advice bc I can't fit enough stick powder behind the 80 & 90 gr bullets and TAC is tight enough that I'm hoping to get the velocity I need. If it doesn't work I am SOL at 1,000y but I see guys online shooting the heavy bullets that fast so I figured it's worth trying.
Don't know why you say you can't "fit enough stick powder behind the 80 & 90 gr bullets". This is wrong. Varget is a compressed load and with the Sierra 80's I loaded 24.5 grains. These were shot from 6.5 and 7.7 twist barrels, .010 to .020 off the lands. Mainly used at 600 yards but when my kid was thirteen or fourteen he shot it at a regional at Quantico (in a new RR) and he beat all the shooters from the AMU at 1000. Came home with the coaches business card and was told to call when he was old enough.
Want more velocity, go with Rel 15.
I swiched to 90's for 1000 but felt that JLK's shot much better than Sierra out of my 6.5 twist Krieger barreled service rifle.