The average reported weight for the 3-Rouble 'Ducat' was 159.776 Grains (~10.353 Grams), probably a fair estimated value for lightly circulated coin.
In France, the estimated weigh for the1828/30 coin was ~10.364 Grams.
Reported in 1843, the Weights of Platinum Roubles, from a Russian collection/publication; updated in 1855: the 3-Rouble of 1833 weighed 159.11 Grains; the 1834 weighed 160.19 Grains. The annual Average Weight is ~159.81 Grains (10.35553 Grams)
Citation: Monnaies et médailles russes, d'après l'état donné par le cabinet du General D'Infanterie..., Fedor Fedorovich SHUBERT (1858)