Sniper vs Armoured vehicle.

[Imp]

You wont find it happen that often chance for a succesful assault on a tank is based on a number of factors. Off the top of my head.
The normals
So Move status terrain suppresion.
A suppresed or damaged target increases chance of success hugely vs vehicles, suppresion equals buttoned cant see squat.
The other big factor in assualts is number of men the more the better.
Lone man might make it undetected, 10 trying even if the tank spots 2-3 some will likely get to it. Several early russian tanks about the anything bow mounted MGs were any use for was spraying the tank in front to stop assaults.
If your playing a campaign with high experience units this will effect the outcome game engine begins to break down when units get much over 100 experience they become to good but using standard units even scoring an immobilise kill with a sniper is very rare vs closed top vehicle. Open top a grenade or shoot the driver followed by a crash would do it.