Well, for one thing, the prices flip-flopped since I was a kid. We used to buy 22 shorts for half the price of 22 LR. Today only a couple of companies still load shorts and when you can find them they cost more than the long rifle. And the intermediate length, 22 long, has just disappeared.
DO NOT SHOOT AMMUNITION IN A WEAPON NOT CHAMBERED FOR IT. If you do, bad things will happen.
Why is there a shortage of .22 ammunition?
22 250 Remington
It's a warning to the user that the only compatible ammunition for that rifle is the .22 Winchester Magnum Rimfire (22 WMRF), and other types of .22 ammunition are NOT compatible.
No one that I am aware of.
.22
No, firearms chambered in .22 short, .22 long, .22 magnum, .17HMR, etc... are all currently being manufactured. These all use rimfire ammunition.
22 Short, 22 Long, or 22 Long Rifle rimfire interchangeably.
If you mean 22 LR, it is the most common ammunition sold in the US. It is available at most sporting goods stores, including WalMart, and every gun shop I have ever been in.
air rifle
More than likely your barrel will say .22 Long Rifle only. So, you can use any .22 Long Rifle ammunition.
The equivalent of 5.65 mm ammunition is .22 caliber ammunition.