Any kind - that's the point of the kit. But you might as well buy cheap stuff, you'll still be able to get a good paint to barrel match.
Affordable, good quality, easy to find in stock
Only one front, lack of colors
Comes in a pretty nice black canvas dual zipper case with the Empire logo on it. The barrle kit pieces sit in thier own cut-outs in a foam bed, so they wont get scrathed up. It's a little on the big side, but it's very lightweight. Nice thing about the case is that is has slots open for 4 more front tip lengths, so you can add those and have a full 11 piece barrel kit. Comes with 6 different sized backs and one front tip that makes the barrel 14" in length. If you play front, you might want to pick up a 10" and/or 12" tip so you can keep tight.
All pieces have a very nice finish, they screw/unscrew without any problems. Very smooth finish when you put two pieces together and look down the inside. It's got enough porting to not be too loud, but it wont waste your air and make your gun a gas hog. With six different bore size back pieces, you are pretty much set. I have shot some really horrible cheap stuff thru this barrel, all dimply and out of shape - I have not had any breaks at all. Because of that, I have no clue how it shoots thru a ball break. With good paint to barrel size match, it is nice and accurate.
It shoots good, is a good quality finish, it's lightweight, affordable, and fairly quiet. What more do you need?
I'm very happy with this barrel kit. I like it much better than my Freak. It is just a lot easier to deal with, and I haven't had any problems with it. Much more affordable than getting 6 Ultralite or Boomsticks. Much easier to find in stock than the Kaner and CP barrel kits (I looked around, but had no luck). The other length tips can be bought for a nice low price, and I'm picking some up.
^^ they can if they are too long. The longer the barrel the more distance it has to get out. the more distance, the more friction . the more friction, the slower the ball comes out. Now you need to increase your velocity to make it come out at the same speed as with a shorter barrel. So, inso facto, it uses more air/CO2.
Also if they are ported the whole lenth of the barrel, more air will escape through them while it is trying to push out the ball. if its loosing air behind the ball, it wont come out as fast and youmust, again, increase velocity.