Hi Kestrel...
The 22 Horner is an old, old casrtridge (circa 1930) - and the first of the "souped up"
centerfire 22 cartridges (like the 218 Bee and the 219 Wasp).
Of course its' primary differences from the rimfires are; it's close to 3000fps, the bullet is heavier (35 - 45gr), it's a necked cartridge case, and it is reloadable. A lot of it's appeal today is nostalgia because it is generally considered to be THE cartridge that ushered in the era of true (factory-produced) "Varmint Cartridges".
The rifle that first gave it a stage upon which to really strut its' stuff was the venerable Winnchester 54 - a very popular rifle from the 40s/50s. A little later, Sako brought out some beautiful "upscale" rifles chambered for it. Wasn't long though that it was eclipsed by the 220 Swift (probably the hands-down greatest 22 varmint cartridge of all times) tearing along at 4000fps.
One thing about the Sakos chambered for the Hornet - they had a bit of reputation for shooting two groups. By that I mean you might shoot 5 shots and have an overall group of 1" (or more) but it was common to see a couple of those shots touching each other and the other three touching each other but on the other side of the "group". Of course that doesn't matter much if the overall group size is 1" or so. But die-hard varmint shooters would get the fantods if half the group was 2" away from the other "half", especially since their Sakos cost such hefty prices.
The Hornet was also one of the rifle cartridges Savage used to chamber in their inexpensive model 24 rifle/shotgun combo guns, making it sort of a "poor man's varminter" in an age when a lot of Folks couldn't afford the rifles chambered for the Swift (and later the .222 Rem., 22/250 etc.).
The Hornet was, and still is, a pretty respectable little woodchuck rifle, its' primary drawbacks being susceptiblity to wind deflection which in turn limits its' range a little compared to the later 22 hotrock centerfires. It's still a fun little cartridge to use... Ya just can't brag to anyone about your "magnum".