these are attractive glasses, and I hope you do have some luck, although as Andy has said the probability of finding the maker is very slim.
From experience, backstamps are unlikely to be in the centre of the foot, especially with a star cut like this which would leave almost no flat area to mark. Far more likely to be around the outside of the foot, if at all. Try flicking with a finger nail - and if they have a nice ring then you have a better quality lead crystal glass, although I'm unsure what knowing their weight will tell us, perhaps m can explain

You might find that there is a little variation in height - thoughout the set - this is not uncommon on older glasses. As you still have the set of six, then I'm guessing they have seen very little use - either that or your gran was exceptionally careful when using them.
welcome to the GMB by the way.
