+1 on the G4009G gunsmith lathe. If I didn't already have a lathe that will chamber barrels thorugh the headstock, that's the one I'd buy. I think it's hard to beat for the money and it has the features needed to support both hobby and professional barrel work as well as about any other lathe task within it's size range.
I've been in the Grizzly showroom in Muncy, PA. I saw both the G4009G and the G0509G, twisted the knobs, looked them over pretty good. I definitely liked what I saw. The more expensive one is nicer (no belt changes required to get all the speeds and nicer feeling lead screws), but the smaller one is completely adequate and would last a life time, or even two. Grizzly stocks parts and accessories (trust me on this, you will spend the cost of the lathe in tooling before it's over) over the long haul - a major feature. Things like a DRO, etc. are very nice additions.
That said, any good quality 12x36 gear head import with a 1-1/2" or larger spindle bore that will do both metric and imperial threads will work. A number of European rifles have metric threads on the barrel so metric thread capability is almost mandatory unless one is going to restrict themselves to strictly domestic actions.
The lathe is the most important first machine tool. Getting one that won't need to be upgraded is a heck of a good idea because not too far down the road you will want a mill ... I did ...