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.
Why is there a shortage of .22 ammunition?
22 250 Remington
.22
No one that I am aware of.
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.
More than likely your barrel will say .22 Long Rifle only. So, you can use any .22 Long Rifle ammunition.
air rifle
The High Standard R-100 revolver uses .22 Long Rifle (LR) cartridges. This versatile caliber is widely available and suitable for various shooting applications, including target shooting and small game hunting. The revolver is designed to accommodate both standard and high-velocity .22 LR ammunition.
.223 Calibre although .223 Will fit on a 5.65 mm, a 5.65 mm Will not fit in a .223 calibre chamber.
The term "s-l-lr" on a Mossberg .22 rifle refers to the types of ammunition the firearm can chamber and fire: "S" stands for .22 Short, "L" for .22 Long, and "LR" for .22 Long Rifle. This designation indicates that the rifle is versatile and capable of using these three different .22 caliber cartridges. It allows for a broader range of ammunition options for various shooting applications. Always consult the user manual for specific guidelines on ammunition compatibility.