Why does .177 exist?

[Muskett]

I have five minutes...so:
I've always thought UK air rifles were six to eight ft/lbs too low powered to be absolute farmyard critter winners. They completely rely on shot placement for dead drop lethal. They have no energy for hydro shock explosive wound expansion that nearly every other vermin getter enjoys. A .22LR even at subs is doing a golf ball sized absolute carnage in any flesh type material. .17HMR causes an absolute orange sized mush mess. 12 ft/lbs air rifles just cause a stiletto wound tract only slightly bigger than their calibre size.
A .177 through a rat is a massive hole. .20, .22, and .25 are just more massive. Heavier vermin can take a "bite" from all four calibres though may die later. So, however you look at it for drop dead it means taking out a vital like brain or heart.

Most air rifles can hit a polo mint at 15m. Heck, even the poor performance ones. After 15 then the "loop" of trajectory has to be catered for. A .177 generally fly at a higher velocity than any of the other calibres. That makes them difficult to see through a scope. Unlike a .22 that can be seen looping off to the target. .25 is so slow its like waiting for a bus. Which just shows just how much faster a typical .177 is going.
The bigger calibres do have their place at the closer ranges. They do give a solid wallop on target. Often they will knock the critter over, though not always dead. Fine if you can pick up and dispatch fast, or have a terrier to clear up. But, in this high ethics age, dropped but not lights out isn't really good enough.
Beyond 15m then hitting a polo mint takes are pretty consistent and forgiving air rifle; one that tac drives. A lot of air rifles are no more than 25m polo mint hitting rifles and for many 20m is more their limit. 1/2" off isn't good enough today.

Modern PCPs now give a far higher level of accuracy with all the calibres. Hunters are hitting vitals far more often with all the calibres. However, the .177 is still flying the flattest at all ranges. It absolutely has the advantage of first time hit on a vital at all normal ranges and even greater an advantage at the longer ranges now attempted.
Given a range finding scope, or laser rangefinder, then all the calibres can be shot to hit the mark. Without range finding aids then most calibres are poor compared to the .177. It is not because the .177 is groovy, it is because they fly flatter and generally accurately with it.

What calibre isn't important, but hitting that vital; is. What range you can consistently hit a polo sized vital is what determines shooter/combos range. Most people will do better with a .177 and concentrating on shooting for a vital properly. A "hit' isn't what is done today. Those more advanced shooters may well get similar results with the other calibres, but they are putting more input into the equation.