Unfortunately, gun stores and weapons websites seem to attract d_cks (no not ducks) and many Youtube or website "experts" are so full of themselves they need Roto Rooter to pump out the feces.
I am very selective as to whom I take advice from. When they cop an attitude that is a huge red flag and it is game over for me.

Well, at least they chose the right name: Unicorn.

I'll bet it would suck if you caught it in the eye or behind the ear or the forehead or....

maybe they figured out how to mount a 9mm bullet in a 50bmg casing

9mm sabot out of a 50bmg. I think you are on to something! 124gr out of something used to pushing 700gr.

https://www.quora.com/What-would-happen-if-you-necked-down-a-50-BMG-round-to-22-LR

http://forums.pelicanparts.com/uploa...1636576353.jpg

I think they need to make the barrel a bit longer than usual to take advantage of all of that powder too. I assume at some point, the friction in the barrel starts to become a problem, but what are we thinking 36" or 48"? Or should be go for the gusto at 60" or 72"?

Then we can write an article about our own magic bullet!

Many, many years ago P.O. Ackley (of the "Ackley Improved" rifle cartridge design) necked down the then new .378 Weatherby Magnum case (just the old .416 Rigby with a belt) to .22 caliber. Purely a stunt, he named it the ".22 Eargeschplitzenloudenboomer". He was unable to get enough rounds down the barrel to even work up a load, much less ever sight it in, before the throat would blow out. He did chronograph 55 grain bullets in excess of 7,000 fps, though.

well not 50bmg case cause he insists he shot 9mm at 5097 fps out of a standard handgun
That would make it the fastest handgun bullet in history

out of a bog standard 9mm handgun barrel. yeah right.

He also says he cannot disclose the bullet weight due to ITAR, and he has ratted on me , my IP is being sniffed as we speak and I can expect a knock on my door early next week.

The guy must have glued up his ammo, and sniffed the glue a few to many times.

You can get the biggest case for the smallest projectile, but none of it will be efficient.
And more then likely it will just blow up the chamber

I know I guy who shoots Extra Long Range
He uses a 308 winchester case
pipes it through a (if remembered correctly) 36 inch barrel custom made with heavy twist.
seated long, heaviest pill

And the Ballistics of his 30 cal are a match for 338 LM
so same flight at well over a mile.