What is the smallest caliber ever produced(with some sort of popularity, not just a one of a kind)?

[officerdom1987]

Every source I looked at, including my reloading book seems to say the most popular, without being homemade, is the 17. I would think the smallest with a larger rifle cartridge may be a .204?

[JM]

@happen97,
Been doing a bit of searching...Found a weapon that shoots a 2.34mm bullet...I do not believe it has any type of popularity though; just a collectible novelty piece.

[habben97]

2.7 mm kolibri was the smallest center fire. it is long obsolete though.

[JM]

And to clear things up I am talking about the diameter of the bullet, not the overall size of the case and the bullet.

[JM]

That is my guess as well, but I couldn't find anything to back it up.

[huntfishtrap]

As far as I know, the .17s are the smallest, but I could be wrong.

[JM]

What is the smallest caliber ever produced(with some sort of popularity, not just a one of a kind)?