Which calibres really made an impact?

I would venture that in some ways the 30 30 , .22 and the .303.

This question is so broad, the .458 Win changed availability of big game rifles, the .22 paved the way from Flobert to 22 Magnum the world wide start shooting rifle.
The 9 mm Parra changed everything in regard to standardization.
The Spenser rifle was the first repeating brass cased ammo rifle, must have changed a lot of things that.
The Snider and Martini henry were also game changers.
The 6.5 Creedmoor was also a big game changer in that it introduced gender flexibility for shooters wanting to express themselves.
The 12 G and 410 shotguns made international ammunition available, every shop had both as standard, as in opposed to what was before and who carried stock for your choice of shottie -4 G - * G - 10 G - 11G - 12/14 G - 12,14,,16,18,20,24, + the 64,55 Maynard.

The 8mm Lebel changed the everything as it was the smokeless powder debut.

So ????????????????????
oh and of course the 50 BMG, introduced a long time ago for the guys that were really trying to prove they NOT Creedmoor types.

Maybe one can add that the first big introduction was the metallic cartridge. Thereafter, the change from black powder to nitro powder.

Then the different firearms and calibres. The Colt revolver in 45, the Lee Enfield rifle in 303 in the English speaking world together with the 9mm and the 8x57 in the German speaking world.

I would agree on the 308 as well. It set a standard for military and civilian work.

The first mid sized military cartridge was the 7.92x33.

The introduction of smokeless was not a caliber ?

The introduction of smokeless was not a caliber ?

Correct, it is part of the bigger picture - a preliminary step leading to the other advances.

The military cartridges (7.62x53R, 303, 8x57) hail from the same era.

This is a cool thread!

Surely the answer must be the point 22, weapons were just hat till the .22. The .22 introduced fun, sport, let me try it. The .22 presented shooting for everyone and anyone without the big bag, without the use to kill factor.
The .22 brought shooting to everyone.

The military cartridges have always been at the forefront of development. The 7x57's success in Cuba inspired the 30-03/30-06 and the P14 action (Britain's response to the Boer war). The 7x57 was a baby of the 8x57. A lot of cross pollination from different countries.