Oval Charm changes the chance a Pokemon will be bred every 256 steps - no affect on the shininess
The Masuda method is possible because of an internal marker on each Pokémon which identifies their "home location", 0x17. If the game recognizes the two Pokémon in the daycare as having different home locations, then the chances of the Egg hatching into a Shiny Pokémon will increase. In Pokémon Diamond, Pearl, Platinum, HeartGold, and SoulSilver, the odds will be increased by five times: from the usual 1/8192 to 5/8192 (approximately 1/1639). In Pokémon Black and White, the odds were increased again, to 3/4096 (6/8192 or approximately 1/1366). This is six times as likely as encountering a Shiny Pokémon in tall grass under normal conditions.Additionally, the Shiny Charm item affects this method, increasing the chance to 1 in 1024 or eight times as likely as normally.
So technically you will need to get 1024 eggs to have 1 shiny. However remember, the concept of probability in mathematics is extremely flawed - in each Egg you will have a 0.0009765625% chance of hatching a Shiny - astronomically small.
Sorry for the maths. lol