Honestly I'm not sure. What I do know is that the Rolex Submariners (1680 and 5512/5513) and the Omega Seamaster 300 diver, which were rated to 200M / 660Ft were at the upper limits of what was possible with plexiglass, IIRC the deeper diving watches of that era either had extremely thick crystals like the superdome on the 1665 Sea-Dweller or mineral crystal as I believe the PloProf 600 had.

The Sea-Dweller 1665 Tropic 39 is just stupidly thick, as you can see below compared to a 5513 Submariner's 5513:



Of the two the Seamaster 300 is closer to the T19 of the 5513, and the dome probably does give it some added strength, but still plastic is plastic.

 

Well I got it back today, $280 later, the crown is so stiff I can hardly turn it, but even when I do turn it, it feels like its not turning correctly, like its not actually unscrewing, and there's no way to pull it out for setting... guess its going back in again...

 

Finally got it set after some muscle and rubber gloves, its just stiffer than hell, but workable. Keeping it on a winder to save me having to rip skin off my fingers for now.

I do love this watch though

 

Why's it so stiff? Did BVW work on it?

 

Yea they did, but I think its just the parts, its 1960s waterproofing technology, and its not the most user friendly.

 

They're a very attractive piece those, the real difficulty is that the condition particularly on the military variants is very ordinary, Mike Wood has several 5517s that look like they never saw moisture, while nearly every SM300 big-triangle dial, even those considered "good condition" have dials that look like they've been at the bottom of a swamp. This museum example is beyond reproach however, and the yellow patina looks exceptional. I really do wish they'd bring this diver back into the Seamaster line.

 

This is a '57 Speedmaster but you get the idea:

 

I really do highly recommend them, they're the most comfortable dive watches I've ever worn, a big step up from anything modern.

 

Looks great on Isofrane too, been debating getting one of those for some time, being a non-rubber guy, I'm wondering if its just the crap rubber straps that have turned me off.