I can't comment on bus bars, since I haven't used them.
But I have successfully clustered 2, 3, and 4 BP motors using Estes igniters with the leads twisted together, without using any extensions of the leads. It's kind of a pain, especially with 4 motors, but it's worked for me so far.
John R. Thro, NAR #84553 SR
I first launched a model rocket in June of 2004 and was *immediately* hooked. Today, I have kits or have built rockets from:
ASP, Custom, Edmonds, Estes, Fliskits, InFlight, Neubauer, PD Rockets, Quest, Red River Rocketry, Rokitflite, Semroc, plus several more scratchbuilt rockets.
After about a year of being pretty inactive, I've got the bug again in the summer of 2011!