Mugsy. There is no such thing as " knock Down Power", either in modern guns, or MLs. If we are talking bazookas, or cannons, then yes, there is enough mass in those projectiles to actually knock something down. The relative weight of a ball or bullet compared to the weight of a deer or man is so small that it can not possibly knock anything down. This is one of those phrases that some gun writer came up with years ago, and its kept a lot of gun writers employed every year since.
As has been noted, that .62 cal. ball is already wider than many of the pistol bullets and modern rifle bullets will every reach after they expand in size. It puts a mighty big hole in an animal, and that leads to a lot of bleeding, and death. Its like an arrow, or broadhead, only on steroids! Now, large caliber bullets and rifle balls do hit more pain sensors in the skin when they hit animals or humans, simply because the body has those nerve ending spaced out about 4 tenths of an inch on a grid for all mammals, except where nerve ganglia are located( the solar plexis is the most commonly known) and of course where the main trunk lines of the spine and its branches run through the body. A hit to any of these major nerves is likely to cause the animal to pass our, and then die of hemorrhaging, without moving from the place it was shot. Hitting such a small target is very difficult at best, and usually the function of luck, only. Yet, many people talk about a gun or bullet having " knock down power" because the bullet happened to hit a major nerve! And, you will hear that someone once killed a grizzly bear with a .22 rimfire. Or they killed a huge wild boar with a shot to the brain through the ear with a .22 rimfire cartridge. Both would be examples of this so-called " knock Down Power, but I don't think any sane person would take a .22 hunting on purpose for either wild boar, or grizzly bear.
When hunting large game, such as the Big Five in Africa, there is often the need to have a bullet that is capable of smashing through a lot of meat, and bone to get to the brain or spinal cord. Those guns will be large in caliber, and also carry powerful powder charges. The same kind of guns can be used to shoot the large bear on this continent, with good results. But, we also have smaller diameter guns that will kill bears equally well, simply because the ballistics Coefficient of the bullets they shoot are good enough to guarantee excellent penetration in the animals flesh and bones.
So, please stop worrying about knock down power. It doesn't exist. What you do want is what you will get from a heavy Round Lead Ball, and that is a very heavy projectile, that will penetrate, and break bones if it has to to cause massive hemorrhaging and death to an animal. The .62 smoothbore is shooting a round ball that weights in at 3/4 ounce! ( 325 grains.) Compare that to those modern rifle bullets, even after they have also expanded. That 62 cal. ball will expand to more than an inch in diameter on some wounds.
That is a huge amout of tissue destruction in the primary wound channel. There is no need for the secondary wound channel produced by high speed, but small rifle bullets.