Dave, I think the chatter issue is when the pilot isn't in the bore using a floating pusher that the only place the reamer is supported is where the shoulder is running in the bore. The dead center gives the reamer support in two locations, the shoulder and the rear of the reamer. With my current lathe, I thought I was getting reamer sized chambers pushing all the way with a dead center. I couldn't feel any sideways movement in the reamer when it was full depth. I cut two PPC chambers for me, one pushing the reamer with the dead center and the other with the pusher. The pusher cut the smaller chamber as I couldn't use brass from the other barrel in it. It had no effect on accuracy, just brass size. After that I at least finish the chamber with the pusher if I don't ream the whole chamber with it. If the pilot is in the bore, I use the pusher. If it's not then I push with the dead center until the pilot gets into the bore, then switch to the pusher. Probably could switch over sooner as after the reamer is cutting on the taper it's supported. Seems like chatter is usually a reamer problem as I've had very few reamers that would do it and you're right they were usually Ackley's. Finishing up a .423 on a Jeffry's case today for a customer's wife in Alaska.