Well 4166 disappointed today in the 6x45.
Where as IMR 8208xbr, has been pushing 2700-2800FPS with my chosen Speer 75gr HP,

IMR 4166 was maxing out at Hodgdson book max at around 2300fps, with very little room left in the case.
tested
21.5gr
22gr
22.5gr
23.1gr --- `2300fps from 20" barrel.
ALTHOUGH this was using 223 data.

There were zero pressure signs at any level.

Looks like I may continue on from here. Accuracy was 3/4MOA with 2 loads going into 1/3MOA groups. BUT velocity just wasn't there.

So the quest will continue. If I can't achieve the desired velocity, then I will fall back on 8208. Was really wanting to have one powder for .223, 308, and 6X45.

IMR 4166 meters perfectly in a Lee Auto Disk double disk set up.