As I was skimming the TechPB newbie forum and looking for common paintball questions to write about, I noticed something I hadn't expected. There were a LOT of questions concerning bore size. What is it? What bore size is the stock barrel of ______? Best bore size? The list goes on. I also noticed that not only new players were asking these questions, but experienced tournament players also had questions about bore size. I went to the Google machine, and couldn't really find any solid sources of information on what bore size actually is. So, here is an article all about bore size.
The basic definition of bore size is that it is the diameter of either a paintball or a barrel. The average bore size of paint and barrels is .68. However, they can range from as low as .678 to as high as .689.
The bore size of paint fluctuates based on the manufacturer, and location of purchase. Shipping and climate can cause paint to swell or shrink, which is why the same brand of paint can have different bore sizes depending on the location. Meanwhile, the bore size of barrels fluctuates in order to compensate for the differing paint sizes. The size of barrels ranges from around .678 to .689.
If a player is using a .684 barrel with .689 paint, they are underboring - meaning that the diameter of the barrel is smaller than the diameter of the paint. If a player uses a .689 barrel with .684 paint, they are overboring - the opposite of an underbore.
Overboring and underboring both have advantages and disadvantages. Overboring leads to a slightly less chance of barrel breaks, and has a quieter shot. Meanwhile, underboring provides greater efficiency, and shoots through broken balls better. Matching the paint to bore size exactly provides no real advantage.
Overall, the differences between an underbore and overbore are minimal. Purchasing a full barrel kit is only a good idea if you plan on traveling a lot or using many different brands of paint. Otherwise, find out the bore size of your local field's paint and find a barrel size that over/underbores accordingly.