whoa, sorry to say this, but it sure doesnt look like you have been here many years… the reason there are jaggy edges is probably because u didnt render it… and if u did, render it twice the size and reduce it in PS. also, press the autosmooth button to make the shading better
I don’t think you need subsurf for this - it’s a mechanical device…most mechanical devices aren’t supposed to look organic but this does with subsurf, it’s too “smooth”. Unless, of course, it’s a turret for Willy Wonka’s chocolate factory
I really like your first mesh, it looks great. Just like the turrets in Star Wars. I’d go without subsurf.
You can add detail to a subsurfed mesh and maintain smooth edges by using loop cut (CTRL + R) and placeing vertices close together near edges and creases. It would work especially well for your gun barrels.