I would say if the 223 PB bullets are accruate in your rifle they would work fine for the deer in your 75 yd range.I have shot more than a few deer with a 45 cal round ball,even shot one with a double ball load once.
Useing my ruger I shot 7 deer in 2 seasons useing a 185 gr nosler bullet all head shots from 25 to 70 yds,used a 225 PB out of a knight disc to drop one at 170yds,hit a little higher than wanted to took out 6 in of spine deer dropped where it stood.Took several useing 200 gr sw and sst with encore no problem from 45 to 100 yds,used a 195 barnes on one large 8 pointer at 100 yds bullet didn't open found a couple days later had shot through both shoulders,looked like a pencil hole all the way through,that was a stinking job sawing the horns off,haven't used them anymore.
I use a 250 gr sst in my savage muzzle loader at over 2400 fps,if I could get the 200 sst to shoot as fast and accrute as the 250 I would use the 200.
In one week this same savage muzzle loader shooting the sst 250 with same load dropped 9 deer,one doe,one 6 pointer,four 7 pointers,two 8 pointers,and one 10 pointer,the doe weighed the least at 135 lbs,were shot at 100 to 234 yds.ALL were complete pass throughs.No I didn't shoot all of them I just shot 4 of them.
Have used the big conicals in 45 and 50 cal side locks also but since the sabots came out I like them and the lighter bullets better.But the big conicals killed deer just as good.