I thought about the idea of making my own brake calipers after working on one of the many old bikes that I have.  I figure if a rustic old sidepull can weigh less than a Dura Ace dual pivot, why not improve on that and you can have something modern with retro mechanics. 
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Some basic premises for the project:

1.  Has to be much stiffer than an old diacompe sidepull.
2.  Must weigh less than 200 grams for the pair, with pads.
3.  Must be as easy as possible to machine (as little setup routines as possible).

And here’s my initial design:
For strength in the arms I simply employed the power of geometry to make it as stiff as possible whilst using as little material as possible.  The thickness of the arms will mean it’ll be stiff against axial loads while the x bracing on the bottom halves of the arms will hold against torsion loads.  The arms are made as simple as possible to reduce machining time.  They are sized to produce about 1.2 time mechanical advantage and work with about 8mm of cable travel as that on a Shimao lever.  That’s about as good as a Dura Ace 7800 caliper. 

Click to Read more about Mechanical Advantage.
Hardware is going to be Titanium with an aluminum recessed nut.  From this angle one can see the simplicity in the design.  The arms can be cut out in about 3 setups with a 3 axis mill.
So far the complete caliper minus brake pads, cable adjuster, and spring comes out to roughly 65 grams.  A 75 gram fully functioning caliper should be achievable and if you didn’t know, that is a ridiculously light weight setup. 

There are some cons to this design though.  First, in true vintage fashion it will not have a quick release.  Secondly, the spring system will have to be thought out carefully or else the typical problem of the calipers going off center will be an issue.  I am also currently perusing other designs that will take even less machining time so if you have any, shoot me an email.

My research has shown that there are two brake calipers out at the moment with generally the same design theme.  One being the Ax-Lightness Orion which uses the same geometric principles as mine but in carbon form so they are able to achieve a world topping light weight.
The other is the Brams M5.  This one is a beast!  It uses more of a beam design and from every review seems to be quite the stiffy. 
Read a great review on all of these brakes at Fairwheelbikes