Did you guys know that each tank has sloped armor. A few updates ago they updated the armor by more hit boxes. A hit box is a part of the tank, for example, the frontal sloped armor on the front of the is7 would be a hit box. Before they had only 8 of these hit boxes but since the patch they had 16 of these. Therefore you can hit a tank in different places and before you may have bounced but now you may find a spot where you can actually do damage now. Since this patch your hit skins are not as useful as they use to be. They can still be used to find the ammo rack and hard spots in the armor but they wont act the same as they use to.... : p 

Happy hunting Luckysniper 

PS:

From http://wiki.worldoftanks.eu/Battle_Mechanics#Tank_Hit_Boxes

Tank Hit Boxes

The Hit Boxes for tanks are hidden from the player, but you can research a tank and pretty much figure them out as they are based on the historical model. For example: the ammo rack hit box is in the same location(s) as they were stored in the historical tank.

The 3D model of the hitboxes, [posted at the forum], leads to the assumption that WoT uses a quite plain system of calculating the hits. Fuel tanks, ammo rack, gear box, transmission, turret ring, gun mantlet, tracks, and obviously the crew. Here are the explanations for the most common strange damages.

Frontal hit, engine down, engine located in the back of the tank -> Engine was not hit, but gear box or transmission were.

Hit once, three modules down -> The shot went straight through the tank/turret.

Hit enemy tank, got a critical, but caused no HP damage: Possibilities

Shot went through an external module(s) (Tracks, view finder, range finder, etc) and then missed the rest of the tank.

Shot went through an external module(s) and then bounced off the armor.

Shot penetrated and went into a module/crew member and caused no damage. This can happen because Maus tracks can fully absorb a 75mm shell. Exact values for this are unknown but the concept that a shell can "lose" damage by hitting a crew member or a module should be remembered.

Shot did less damaged than expected. A shell can also strike a module/crew member and continue on (at a reduced speed and reduced damage). Reduced shell speed will reduce the shell's penetration values (possibly causing a bounce).

Shot hit a tank and you got a message from the group "armor_pierced_by_player" but the shot did no damage. This can happen when the shot re-damages tracks or a module (thus, no critical). It should reset the repair time (unconfirmed).

Module Damage

When a module is hit, it effectively gets a "saving throw". If it makes the "saving throw", it takes no damage. If it fails the "saving throw", it takes damage. If the damage is large enough, the module becomes damaged. If it is larger still (more than the modules HP), the module is destroyed. Damaging a module does not reduce the HP of the tank.

The chances for the loss of a module:

Engine: 45%

Ammo rack: 27%

Fuel tank: 45%

Optics: 45%

Radio: 45%

Gun: 33%

Turret ring: 45%

Crew: 33%

The amount of ammo you are carrying does NOT affect the chance of taking an ammo rack hit.

Crew Damage

Crew are either alive or dead (knocked out, injured, etc.), effectively speaking. A Crew damage does not weight too much against your tank. Crew may be healed with a health kit, during which they function at full effectiveness.