Rob,
I went to Hornady and used the 140gr/ .646BC vs the 147gr/.696BC in the 4 dof calculator with 2820fps and there was a .3 mil difference at 1020Y. .2 mil is a 7.2 inch group which isn't easy to lay down at 1000Y. I'm not doubting your dope was correct but there are other factors to consider that could cause more than a clicks difference, like which side the wind was blowing from - affecting the vertical, what temp it was that day/ammo temp(adjusting to 2800fps fps changed the calc .15 mils), and if your zero was perfect, heck even scope tracking could be off a tenth???
I tried googling the article that I read which was about twist rates affecting BC's and couldn't find it. I thought it was a Hornady article??? Maybe someone else knows where it is. I was trying to figure out what possibilities there could be for why Sean's 147's landed short. I did see that the 225 ELDM 30 cal has a .777 BC with a 10 twist and a .798 BC with a 7 twist.
I do fully admit I'm definitely no ballistic expert. The same factors I mentioned could have affected Sean's dope as well???