for getting the smoothest buttercream ever?
For me it's a must to have a big scraper and a turntable. After it crusts, I like to use the viva method. http://www.thatreallyfrostsme.com/2010/04/smooth-buttercream-frosting.html
what type of buttercream are you using?
I use a crusting american buttercream and I only use the Melvira method. That's what I used on this cake and it even allowed me to go without borders