The diameter as well as the weight enters into it so does the construction of the bullet.
Diameter to weight ratio is call sectional density you will find that by looking for it you can find the SD or sectional density listed with the BC often.
You will also find that the 200gr 40 caliber bullets with compare to the 300gr 45 caliber bullets and that the same construction bullet like two Shock Waves should given exactly the same circumstances will give much the same penetration.
Where one of the differences comes in is that you can push a 40 cal. 200 gr. quite a bit faster with a max load.
An other thing you must take into consideration is that some bullets have a speed limit faster than you can push them. Many years a go I used to use PB and since the 245 had a much better trajectory I tried to make it work for me but when you push it fast enough to get it to shoot flat enough it disintegrated or fragmented on impact so I had to modify the bullet to get good performance out of it. what I did was plug the hollow point with lead for deer and a brass plug for bear and elk so that it would penetrate and mushroom in the proper relationship.
A comparison of a pointed full metal jacket bullet and a hollow point can show you that difference. A happy medium or compromise is necessary most of the time, there is more than one school of thought and more than one need for deer a hollow point that does not break up but usually has enough penetration to get out the other side is what I consider ideal for deer. But I would not be likely to use the same bullet for buffalo. To give an example a 250 gr Gold Dot hollow point is a very good bullet for whitetail deer but to get just the right combination I do not use more than 110 gr load of BH where as if I were going buffalo hunting I would use a 275 or 300 gr Lehigh with 140 gr of BH. The Lehigh is in a category by itself it open explosively then gets max penetration in the form of a wad cutter which pushes a considerable shock wave in front of it [I used one on my buck this year on a long angle running shot went in next to the left ham and was sticking out in the skin after breaking the right front shoulder] he was running pretty fast and only got 25 yds about half of which he skidded on his side. There are many things to consider when it comes to bullet construction and shape. There is no such thing as one bullet being good for every thing, the bullet needed for elephant is the opposite needed for varmints and most other game falls in between. Lee