Hello,
I do not like to disappoint collector and did not want to be "too direct" when I said "never seen that type of breast star" for the russian White Eagle order, but as Sergey I must say this is a fake or a fantasy order.
After collecting for 30 years, I have never seen a metal russian breast star of the 18th century - the first known metal breast stars are dated from the beginning of the 19th century and all of private manufacturers (all the official stars delivered until 1855 were embroidered). After some researches, the hallmark ("octopus") is apparently totally unknown. About "top expert" I would say that the real experts in russian orders are very few on the market ... especially in France where it seems you are from, best experts are very often the collectors themselves but not the declared experts on auctions (see Drouot "funny" experts) or the "experts" merchants.
If not russian made, your breast star could have been made in Germany, Austria or France (mainly those three) but those are generally quite easy to identify and yours does not look like as any of those european models.
That does not mean, if you are the owner, that nobody will be interested in your star (we see so very amazing & surprising transactions on a well known auction site :-)