I tried an INF unit and got as far as Kiev where there is rail station. But could not get to Bryansk for the same reason as the rail gun.
New to the game and running recently purchased version 3.0.1.0 so this issue may have been reported earlier.

Moderator: Shannon V. OKeets
The ZOC from the Russian 6-3 INF blocks the rail move to Bryansk. No bug.Your rail move can only enter or leave a hex in an enemy ZOC if there is a friendly land unit in that hex both before and after the rail move. Its move must stop when it enters an enemy ZOC.