Summit 14x40
I bought my current lathe ~20 years ago, the company is still around, but I think their smallest machine now is a 16x60. For the uninitiated "14x40" means you can turn a 14" diameter piece, 40" long between centers. That's a bit overkill for gunsmithing, but for general use I'd want at least 36" between centers unless I was sure that I'd exclusively work with shorter barrels. My lathe has a nearly 3" spindle bore (hole through the spindle) - whatever you pick should be big enough to put your thickest barrel into, or you'll forever regret it. Mine is a gear-head. On the one hand it won't slip or stall (if, for example, I were to get tangled up in it...) on the other hand, the headstock is too long to put most barrels through. That may or may not matter depending on your theory about how best to chamber a barrel.
My lathe is about 4500# and I've had the "pleasure" of relocating it twice (actual moves, not moving it around in the shop). Those times make me wish (momentarily) that I'd purchased something smaller. But, I suspect the next time my lathe moves I'll be gone, or nearly so, so I no longer entertain those thoughts.
I've got all the accessories (and more) don't let those drive your decisions, they can all be purchased after the fact *except* a taper attachment - if you really need one, make sure you can get one for your lathe, or be prepared to design one (which might incorporate changes to your cross-slide if your lathe wasn't designed for a taper attachment. In any case, I find myself cutting tapers with tailstock set-over for the very few I cut. (and I have a taper attachment). DRO, toolpost, chucks - you can get 'em all later if needed.
If I could go back and do it all again I think I'd go with the same machine. I almost bought a SouthBend 10" toolroom (back before SB was purchased by Grizzly) - I'm rather happy today that I bought the lathe I did.
If I were shopping I'd want:
At least 30" between centers.
At least 1.5" spindle bore
D1-x spindle (i.e. not threaded - just a matter of preference)
All else being equal, a shorter headstock.
The Grizzly branded gunsmithing lathes are not bad. I've looked at three instances of the G4003(G) and it seems like a pretty good machine for the money. Haven't seen the larger ones or the Grizzly/SouthBend models in real life.
GsT