It should also be pointed out that modern screwgates are much less prone to locking up when tightened under load than old ones.
Older carabiner gates used to tighten directly up against the top curve of the carabiner; that meant that tightening the carabiner under load, while slightly stretched, was almost guaranteed to jam it up.
Modern carabiners have a stop which prevents the gate from being tightened up against the curve of the carabiner. Consequently, they can routinely be tightened up all the way, and even if tightened under load they _shouldn't_ jam. Of course, the carabiner is still changing shape under load so it can sometimes jam that way, but usually not and less severely.
It's a 'modern' carabiner if you can 'click' the gate when it's done up tightly.