You most likely have a good point. I take the view that it’s not bullet diameter but rather bullet energy. How much energy does it take to effectively disrupt an animals life function. For deer I look for a minimum energy of 930 ft-lbs., if the deer is small possibly 800 ft-lbs.
I have a 85grain cast ,243 bullet which if pushed to 2000 fps yields about 755 ft-lbs for me that amount of energy is to low even starting at the muzzle. I have a 205 grain cast .303 bullet which I push to 2000 fps which yields 1,821 ft-lbs and I’ve proven to myself it can stop a deer. I load 200 grain cast bullet fot the 30-30 which runs around 1,800 fps and it yields 1,439 ft-lbs which should do the job quite well. If I drop to the 170 grain bullet at the same velocity I’m looking at 1,223 ft-lbs at the muzzle and something over 1000 ft-lbs at a 100 yds., which puts things still over the minimum standard I work towards.