All of our pens are refillable. All of the ballpoint style pens use either a Cross or Parker style refill (see above post to see the differences).
Sierra-Style Pen
A "Sierra" style pen can be identified by a single barrel on top and a long metal section on the bottom. Here's a quick video that shows how to change the refill in one of these:
Bolt Action and Cigar Style Pens
These pens are the easiest styles to change the ink in. They both use Parker(tm) style refills. To change the ink, simply unscrew the tip. There is a spring on the end of the refill. Careful when you pull the top off that you don't lose the spring. Remove the spring and place it on the new refill, in the same orientation you took it off. There is a subtle difference in the ends of some of these springs, and correct operation of the pen may depend on which end of the spring is in which direction. Slide the new refill in the barrel and screw the tip back on!