Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2831038.
This box will hold 100 .22LR rounds. The insert sits down into the box on a lip and the lid slides into the grooves. Pull the lid back one row at a time to dump out just what you need. I have also included a photo of a cross-section that I printed for testing purposes so you can see how everything sits within the case. The box measures 166mm long x 46mm wide x 32mm tall.
UPDATE I have added a second, smaller version of this ammo case that holds 20 rounds instead of 100. The files are marked _x20 so... enjoy :)
UPDATE #2 I have uploaded a version of the sliding lid that is 0.3mm thicker. The original was just a little too thin after it is slid back and forth a few times. Use whichever is right for you, depending on your printer.
Another Sketchup Model - Debunking the Myth that Sketchup is Useless in 3D Printing