I don't do gun engraving, but if you are new to engraving I would suggest it take quite some practice before staring on guns.. even though it´s not my business.
I have both the PC and Goliath vise.. both TrueCenter CamLock and they're really great, but they are hard to get..
The PC vise would probably be to small for guns, but a little easier to get.. I have seen some Goliath 2nd. hand, but not too often. I don't know if the Titan vise would be available, but it´s for sure a big stable monster that should handle anything. The low profile turntable vise could maybe be an option as well.. but you would have to check the page and see what´s available.
You would need a heavy and stable vise for guns I guess. Stability goes for everything.. Good luck!
I use a Lindsey handpiece with GRS low-profile ball vice and satellite table for jewellery/trophies/watches and, while I haven't done guns, I'd wager it's too light for doing gun engraving. Maybe handguns but almost certainly too light for doing anything like shotgun barrels (might be wrong though). It comes in at 23lbs so I'd say aim higher than that.