I have 15 bikers. Grav guns seem to be better and more entertaining fluffwise. Thus, I am chopping my own up out of meltas and Necron Warrior gun ends. This way I also get melta barrels for Stenguard conversions. Win-Win!
An Ironclad out of a Venerable Dread that I traded with from my buddy, Viking Librarian. I bits ordered the Ironclad accessories, slapped on a fin for good measure, and converted a chainfist out of a Plasma cannon arm with a chopped up Ork Deff Dread weapon. Chose to repose the fist in a cheesy "Come at me, bro" pose.
Also, I couldn't resist a Chapter Master on a bike. I love Orbital Bombardments. The fin is an Ork knife. The Relic Storm Shield is a Venerable Dread face plate that was trimmed down. The tooth part on the front wheel is the gob from an Ork killer kan. The back banner is from the Ironclad Dread kit. I went Powerfist over Thunder Hammer for cool looks.