The cap for this Raw Brass Space Pen is an actual .375 H&H Mag Shell. A special gift for the hunter or outdoor enthusiast. Imagine being able to write a date on your calendar without your pen skipping. This is just one of the many challenges Fisher faced when it attempted to create a pen that could work in outer-space. The Space Pen utilizes revolutionary technology to make sure it performs in a variety of situations. Upside down, its side, through water, or in extreme temperatures, the Fisher Space Pen contains a sealed pressurized refill (SPR) that will perform. Even if you aren't a space explorer, the Fisher Space Pen can guarantee you can record every event of your next adventure without a second thought.