I will second Inline Fabrication too. I have their roller handle on my 450, which hasn't been upgraded to a 550 chassis. It does have the upgraded powder measure and priming system though. The roller handle works very well. And I also use the Inline Fabrication 4" tall Micro Ultramount with quick change base plate assembly with my 450, my Redding T-7 and my RCBS bench mount priming system. It's really sturdy and mounts everything very solidly.