Need some help on 45 Cal. FN speeds and drop

[delta1]

I have a really slow computer so need some help. Here is what I know and what i need some information on.
Rifle is a Pedersoli Buffalo model with 30 inch barrel
Red river medium range rear tang
Globe front.
Full load of 70 grn. Goex FFG is at 28 on the Red River at 100 yds. The sight setting at 200 yds is 47.
Temperature when sighted in was 40F
The bullet is a flat nose 500 grn. cast at 40-1. Five round groups at 200 yards are from 1.5 ctc to slightly under 2 ctc if i pay carefull attention.
questions are this.
What is the average B.C. of the flat nose cartridge?
What bullet speed do I have?
Reason for asking is I want to hunt with this round and would like 25 yd increments from 100-200 yds.
Regards

[rintinglen]

To calculate what you want to know would take careful chronographing at various ranges and much more information than you provide. Ballistic Coefficient is relatively meaningless in this context. A relatively high (for cast) B.C. of .389 gives only about a 2 inch advantage over a low B.C. of .250
By my best estimate, your load should be giving about 1400 feet per second, with about 30 inches of drop from 100 to 200 yards, based on the performance of other similar boolits charted in the Lyman Handbook of Cast Bullets, 3rd edition.
My best guess for sight settings at the distances you describe would be as follows:

125 yards = 32
150 yards = 36
175 yards = 41
200 yards = 47
I would set a target at 150 and check that before I went afield though. You velocity could vary markedly based on your bore size, rifling condition and twist, ambient temperature and other stuff I'm not remembering. That could markedly alter things.
Good luck on the hunt!