Currently available: 
 
Gen 1 Hard Rubber Adjustable barrels fitted with our Hard Rubber center ring.  These barrels sound as described but their haptic feedback isn't as defined as our current Gen 4 production.  
 
Gen 4 Delrin (body material) Adjustable barrels with Aluminum Tuning Ring.  These barrels produce a slightly darker tone, and they are quite sturdy.  Center ring color options are:  Blue, Purple, Orange.  If you don't ask for a specific color in the remarks at checkout, that's okay because they are all beautiful - let us decide.