Why does .177 exist?

[angrybear]

They use .177 because that is what the rule book says they must use, nothing else if the rules changed they would switch and then you'd be posting the same about whatever that new cal was

That is very true But Why did they choose .177 when other calibers were available,?

Because, as I said in post #20 it's a follow on from parlor/gallery shooting with Floberts & Zimmerstutzen,
which had already settled on 4.3-4.5mm as an accurate size of projectile for their available power.

BSA simply adopted what was already being used, for air rifles designed to do much the same, indoor parlor shooting, but without using a "blank" cartridge for each shot.