Once upon a time, geocaching was about searching for stash-filled weathertight boxes out in the wilderness... Nowadays, one is as likely to be searching for so-called 'log-only' finds- much too small for item exchange, but (to some) no less interesting for their increased difficulty of detection. There are scores of designs for this sort of 'cache' out there, and to that number I add my own herewith. Including a magnet in this micro cache is not strictly mandatory, but it allows for much more creative hiding possibilities.
I used the spent shell casing from one .22LR bullet and one .22WMR bullet. I suggest that you use a spent casing because the primer in an emptied out but as-yet unfired rimfire bullet (of either type) poses an explosion risk. There, you've been forewarned. In addition to the shell casings, I used a small rare-earth magnet, some glue ("Shoe-Goo", in this case, but any comparable adhesive will suffice), a bamboo skewer and a smallish piece of paper.
Step 1: Bullet Points...
I've already stated my recommendation to use spent shell casings, but I don't mind repeating it here. Don't use unfired bullet casings, ok? In the History of Bad Ideas, it's not exactly a major milestone, but it nonetheless runs counter to good sense. Discharge the bullets in a safe and responsible manner and location.
I noticed after a shooting session that even though both of these bullets are .22 caliber, the .22 LR shell actually fits (snugly) inside the .22 WMR casing. The ones I used are Remington (.22 LR) and Hornady (.22 WMR), and I didn't need to alter either casing in order to make them fit 'hand in glove' as they so nicely do. Depending on the manufacture of the bullets, you may need to lightly sand the smaller casing or use a largish screwdriver to flare the opening of the larger casing, before fitting them together.
Step 2: Add the Magnet
So: I have no idea where I got these magnets. I don't know if I bought them or if I scavenged them from something. But these kinds of magnets are pretty easy to come by nowadays. It is not a snug fit, so I needed to fix it in place in the larger (.22 WMR) casing using some glue. I found that my old tube of "Shoe-Goo" did the trick here. In order not to foul the casing -and in so doing making it impossible to nest the smaller casing within it- I applied a small glob of glue on a bamboo skewer and oh-so-carefully pushed the glue-end of the skewer into the casing. The idea is to apply the glue to the very bottom of the casing, but not on the sides. Once the glue is in place, I dropped the magnet into the casing and left it to dry/set/cure.
Step 3: Insert Paper and Go Hide It!
After a few hours (just to be extra sure the glue is all set), you can try fitting the two casings together. Assuming you didn't get a bunch of glue on the insides/walls of the casing, the casings should fit together just as they did before. Now, just cut a strip of paper (I didn't measure it, but it's maybe 1/2" wide and 2" long) that you'll use as the 'log sheet'. Insert the log sheet into the smaller casing and fit the pieces together. There you go. Now: find a clever place to hide your micro cache, publish it to geocaching.com and enjoy reading the reports of frustrated and triumphant geocachers...