Originally Posted by
Vaang
Well, there were several different types of Reynolds 753 available with wall thickness between 0,7/0,5/0,7mm up to 0,8/0,5/0,8 mm (iirc there was even a track version with 0,7/0,3/0,7mm available).
See also the Retrogrouch Blog on 753:
"Not all 753 was drawn to ultra-thin walled gauges. Even from the beginning there were a couple of different gauges available. The thinnest was more common in smaller frames, while larger frames would normally have slightly thicker gauge tubes."
Also a lot of the weight comes from the lugs! Your Look uses the heavy microfusion variant, comparable Peugeot models with stamped steel lugs weight around 150g less
I don't think 753 was ever really drawn out to 0.3mm. 0.5mm and 0.3mm are misnomers when it comes to Reynolds, as they're actually ~0.56mm and ~0.38mm as the metric labels were just nominal and the tubes were specified in SWG, until they went actual metric gauge. I know SBDU got special access, but in the 70s I believe for the most part there were basically two metric variants, 80s had the two R/T variants, and 90s looks like it got consolidated to one (all of these had thicker downtubes than top tubes). Decals look 80s style so if the tubeset is straight from catalog specs, it should have an R or a T. T is the metric only super lightweight stuff. R is the one similar to 531SL that could be imperial or metric.
Other examples of this frame seem to be 753R variant, and as noted fittings can make a bigger weight difference than the tubes, so it isn't surprising that it weighs similar to an imperial 753 frame which would also be 753R. If I recall correctly, 753 tube sets had a straight gauge 531 steerer, such that you could mount a quill stem in the bottom of the fork.