I use 4166 in my 6gt with Hornady 108 eldm. 33.6gr puts me right at 2929fps under 1/2" group at 100 yards. Try the hodgdon reloading site, they had 13 load combinations using 4166 in a .243 winchester. https://www.hodgdonreloading.com/reloading-data-center?rdc=true&type=54