Help modeling a bullet

I am working on an FPS game. I am currently modeling various bullets for use in the game, starting with a 9mm round. Now, I am using the official measurements of the 9x19mm parabellum round and have blender set to metric.

The total length of a 9mm casing (just the casing) is supposed to be 19.15mm. I start with a “circle” primitive and then extrude along the z-axis. But, for some reason, my casing looks far shorter than an actual 9mm casing.

The total length of a 9mm round, bullet included, is 29.69mm. However, comparing the casing I made to a cylinder of exactly 29.69mm, the cylinder looks closer to the apparent length of the real life casing. What is going on?

Are these measurements wrong? Or is blender not scaling correctly?

Maybe check the diameter of your circle? The Circle primitive lets you input the radius (diameter / 2). So if you put the diameter in there the actual diameter will be twice the size you want. You can check the dimensions of your model by toggling the sidebard (Hotkey: N). The dimensions of your model will be at the very bottom.
Screenshot from 2020-06-28 16-48-55

If you entered everything correctly it could also be because of your camera settings. Different Focal Lengths can make objects look differently (wider , narrower, etc) due to perspective projection. You can change the Viewports Focal Length in the same sidebar menu by clicking on the View Tab and it will be at the very top.

Hope this helps!

@nidus is most likely correct. When creating your circle you can type 19.15/2 into the Radius field to get the correct diameter

Oh man, I feel kind of dumb right now. Thank you.