If it were me, I'd try 3 shots with 66.0 grs at 3.310" and 3 shots at 3.325". (Make sure this length fits the magazine and cycles).
I'd also try 3 shots with 66.5 grs at 3.310" and 3.325".
That should tell you what your rifle likes.
JD338
As already mentioned, it's powder burn rates.
I have used H110 in my 44 Rem Mags for years. 23.5 grs with the Nosler 240 gr JHP is very accurate and effective on WT deer.
JD338
Gil,
Congratulations to your daughter on the rabbit and to ion the green head. I understand what you mean passing up shots. I've passed on wood ducks on my pond because I didn't have a way to retireive them.
JD338