GnB was the first barrel I designed that was produced in a production batch. While I can take some credit for the design, we had a lot of help with some of the broad details from Punkworks (Cockerpunk et all) and Bronc, to name a few. Going back down to basics, this is essentially a two-piece barrel, but with an unusually-long back section. At the time this was the longest "barrel back" you could find, which we found worked best with low pressure markers that operate aroud 200-psi. Skippnig ahead to current days, the idea of a longer barrel back section has caught on and many other companies feature something similar. Other features of the barrel include Autococker threads, double-male threaded back, and linear patterns of large-diameter porting. The barrels changed cosmetics over the years, but the underlying design remained the same.
For me this was an interesting project because I didn't want to create any new barrels when the idea was initially being tossed around. I figured there were plenty of other companies already making good barrels. However, after the barrel was put to the test, we found that they functioned very well, and the concept of underboring did indeed yield actual performance increase, so long as the circumstances were correct. Underboring is a somewhat controversial tactic when choosing bore size, and can sometimes produce barrel breaks if the paint is too weak, but when done correctly there's a noticeable velocity increase even when all other variables are identical (pressure, dwell, etc).
Barrel version 1.5 (2010):
These barrels were designed alongside the TAS 4B bolt kit, meant to fund the development of other TAS items. Although I manufactured the bolts, I did not make these barrels. I lacked the necessary machinery, so I didn't want to make a substandard quality item by using primitive methods. We outsourced the work to another machine shop. The final products were of very nice quality and I stand by them.
Barrel version 1.6 (2013):
It was decided to re-design the barrel cosmetics during development of the Zealot marker. The barrel backs changed more than anything else, featuring a very curved shape and more noticeable ball-rounded cuts on the outside. The barrels were still engraved around the back, and the front still have a similar set of ports. One small functional change is the barrel backs are now Autococker-threaded on both ends, so they can be reversed. For testing purposes, we made several front sizes to offer a variety for experimental purposes: the standard size of 14" was still present, but was now accompanied by a shorter 12" front, and a longer 16" front. I would have made an 18" front too, but it was too long for my machine.
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Availability:
We only made one production batch of the original GnB 1.5 barrel, so those are the only kits that were ever available directly to the public. Going forward, the barrel project wasn't renewed due to the costs involved, and unfortunately I can't say if we'll ever make more of them (especially now that a handful of other companies produce barrels that are similar in design).