Markings
Short, Long & Long Rifle would be my guess
Good guess....you win. These are calibre markings for the rifle. Some rifles, particularly semi-auto .22 calibre rifles are designed to function properly only with .22 long rifle cartridges.
However, single shot, some repeaters, and a few semi-auto .22 rifles will work with all three. Older Mossberg rifles had a moveable spacer at the front of the box magazine that could be moved backward or forward to properly accommodate the different lengths. However, when firing the .22 Short cartridges, it was recommended to use High Speed cartridges in the semi-autos so that they would have enough power to work the action.
Some tube fed .22 rifles will fire all three interchangeably, and you can mix them up in the magazine....eg. Remington 572 pump, Cooey 60, etc.
Remington 552 semi-auto .22 rifles will function with all three. This rifle uses a "floating chamber" to generate enough pressure to make it work.
Of course, single shot .22 bolt actions will take almost anything you can stuff into the chamber.
The .22 Short is not generally as popular and used today as it was 40 or 50 years ago, and the price of the ammo is generally about the same as .22 Long Rifle ammo today.
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