Why are there different calibers and weights of projectiles? Simply put, to vary the “power” (in foot pounds) you deliver to the intended target at the end of the projectiles flight based on its speed (terminal velocity).
Look up a picture of a lineup of common rounds. As the case gets larger it can hold more powder and propel a larger projectile down range, often farther. Once again, it’s all about terminal velocity. E=MC2, energy (in foot pounds) is equal to mass (weight in grains) times velocity (speed in feet per second) squared.
If anyone has researched the effects of speed and weight on a rifled projectile it’s the military. During WWII the round of choice was the 30-06 in the M1 Garand. By the time Viet Nam rolled around the military had moved to the 5.56/.223 (not identical but nearly so). Why?
The short answer was that their studies concluded that most armed confrontations occurred at less than 500 +/- yards. The 5.56 has enough power (terminal velocity) to achieve the intended effect and, being lighter, troops could carry more ammunition into battle for the same given total weight.
They did discover that occasionally there were snipers that would take up position just beyond the range of the 5.56. The military has now moved to a designated sniper formation where one member of the platoon carries a 7.62/.308 which has an effective range of 1000+ yards in the hands of a trained marksman.
If you stand 10 feet from me and I hit you with a tennis ball you would scarcely be moved. If I hit you with a bowling ball at the same speed and distance you’ll be knocked off your feet. By varying the weight and speed of the projectile you can choose the amount of power you deliver at the target
As a projectile travels through the atmosphere drag, caused by friction with air and gravity slow it and pull it downward. As with the bowling ball, a heavier projectile traveling at the same speed as a lighter projectile will deliver more power at the end of its flight.
You can’t kill a deer with a BB gun but you’ll disintegrate it with a cannon. You need just enough power to kill it quickly and humanely. If you’re chasing a wounded deer through the brush you should put down your firearm and go home. You have no business being there.
You take this one step further to choose a caliber for the task at hand. The science of size and velocity of a projectile for the distance and weight of a target fills volumes and drives an entire industry.
In general your smaller, high velocity rounds such as the .223, .22/250, .243 and .270 are suitable for small game and varmints as well as small deer like the whitetail. As you move above the .30 caliber spectrum you move to those suitable for mule deer and larger game. For even larger game such as elk you move into calibers such as the .300 Winchester Magnum or the 7mm Magnum.Many of these overlap in their use. There is always the hunter that claims to hunt elk with a .270.
Given all this, legend grows up around certain weapons and their calibers. There are those who collect some or all. I’m a tool guy. I use a 20 oz. framing hammer to drive a 16d nail, a 16 oz. claw hammer to drive finish nails and a tack hammer to drive…well…a tack.
I want a large enough assortment to do all the jobs I have but small enough to keep down cost and the size of the tool box small. My safe contains one .22LR semi-auto rifle, one 5.56/.223 AR15, one 7.62/..308 AR10 and one .338 Lapua Magnum, Bolt Action Rifle.
The purpose of the .22LR is multi-fold. It is an adequate round for small game and varmint hunting. It is also stellar for providing suppression fire at close range. Though not powerful by defense standards it is cheap and I have yet to see someone say, wait, that’s a .22 and walk into the oncoming fire. Together with the rest of my firearms I can protect my family, out to 1700 yards if necessary and further if I hand load rounds.
Study, ask questions and compare opinions. You’ll eventually arrive at the ideal assortment for you and that is what it’s all about.