Bought 40cm chambered for an an np or stryker (whichever it worked with). Unfortunately it is incompatible with the worker metal kit for the np. However it worked very well in the stryker once I cut it down to about 33cm.
I purchased two 40cm chambered barrels, one for my Caliburn and one for my Talonclaw. I started with my Caliburn and it fit perfectly, adding 20fps with just the barrel change. I then cut down the second barrel to 12" and replaced my Talonclaw barrel, again it boosted performance by 20fps. My favorite feature is that darts (unless they are worn down) will not fall out of the muzzle when the blasters are pointed down.
The only tradeoff is that these barrels do not work well with wide headed darts (like Dart Zone/Adventure Force Waffles), but I knew that before and am okay with it.