For me it's still a toss-up between 1731 and 1751. 
Here, I provided a line-up with few examples pulled off the net. I put t0rress' coin on both ends, and in between put two of each dates. For each year one looks obviously different, the other similar!

OK, now some info. These coins were struck at Ekaterinburg and Moscow mints but bear no mintmark, so they cannot be identified by mint.
1731 values at $3 for VG (lowest grade available in Krause)
1751 values at $6 for VG
(Although it would be a stretch calling this coin VG)
Here, I provided a line-up with few examples pulled off the net. I put t0rress' coin on both ends, and in between put two of each dates. For each year one looks obviously different, the other similar!

OK, now some info. These coins were struck at Ekaterinburg and Moscow mints but bear no mintmark, so they cannot be identified by mint.
1731 values at $3 for VG (lowest grade available in Krause)
1751 values at $6 for VG
(Although it would be a stretch calling this coin VG)



























