Every Caliber You Can Dream Of ?:

I recently said that there was a metallic cartridge in every caliber .. sized for just about every need .. (Link:  https://flicense.blogspot.co.nz/2017/09/a-super-magnum-327-federal-magnum.html  )

- So - after worrying about that for a while - I thought that maybe I'd better check that there aren't really any gaps on the shelves that need filling.

Using the 2018 Gun Digest - page 353 Centre-fire Rifle Cartridges & starting with the first & smallest round listed  .17" Hornet - I followed one-by-one each line entry in the tables up to  .50 BMG and (phwww!) sure enough, I didn't find a single gap of much more than '25 thou'. between any two different sequential  bullet calibers.

What Seems Like a Gap isn't .. 

Between .17 and .22" There's .204 Ruger (5mm) @ 4,225ft/sec. 😙

- In the pistol calibers between .22" and up to .50 S&W Magnum there is a smaller range with marginally larger gaps but I couldn't identify any gaping holes.

So it seems that shooter's needs are well served by the makers .. except that not every caliber will be catered for in all currently offered firearms. The only true openings for new cartridges are as improvements on the earlier versions.

0.025 inch is not very much difference in size to get excited over (0.0635 centimeter) .. that's about twice as thick as a hens egg shell or half as thick as your finger nails.

If you could slice ham off the bone that thin - your knife would have a good edge eh.

However ... Below .17" caliber I do see that there are several "wild-kitten" .14" calibers

.. and there even has been a 0.10" :

American Bill Eichelberger has produced sub calibers from 0.14 diameter, in fact .144, .12 ( .123) and even the diminutive .10 ( .103 ) bullet diameters, - that’s tiny!

The .10 Eichelberger Squirrel made from .22 Hornet brass, uses a 7.2gr bullet and 6.5gr of W748 for a velocity of 4,000fps. 

Is this the smallest caliber known at .103"diameter ?

- There's always got to be some clever soul eh,

There's obviously 'other stuff' to consider than the projectile's diameter .. you'll all be listing weight, shape, velocity etc - but at my low-tech level as a rifleman I'm guessing that the cartridge case takes Number 1 importance as in it's size & strength and all those other factors that I know naught-about.

 - But there really is plenty of overlap in the spread of choices laid-out for our delectation (that's a nice word eh .. DELECTATION). - If you hear two guys with gun cases arguing about the superior characteristics of 6.5 Creedmoor over 6.0 Creedmoor - you might guess that they know a lot more about long range shooting than I do.

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I don't get-it:

Just before I close - I'd like to ask - what is it that differentiates between "winners & loosers"?
The .308' and "Thirty Calibers" ( -in metrics these are properly called  7.62 mm.) are widely praised as full power rifle calibers that can do anything you want.. However in handgun lore - this self-same 7.62 / 7.65  ('thirty-two') pistol caliber has been reviled as inadequate and puny by most experts - despite performing competently as both law-enforcement and military issue side arms over more than 100 years?

Marty K.