I'm writing a walkthrough for the game right now, here's what I have for that bit:
Go left to find some ammo, then head right and kill the enemies, climb
up the carriage and head right to be trapped by four enemies; two
soldiers and two snipers, just stay near on the blocks on the roof,
and you won't be hit by a sniper, kill the two soldiers on the roof,
then jump up and fire down to hit the snipers. Continue heading
east, get up the carriage, then watch out for the shells being fired,
get past it, then kill the enemies around you, jump over the boxes,
and collect the health.