Beldum's best moveset in Pokémon GO is Take Down and Struggle, with 5.55 damage per second, and it can deal 76.4 damage before Beldum faints. This is true when battling in neutral weather.
All Beldum movesets ranked
Here is a complete list of Beldum movesets in Pokémon GO, ranked by their DPS and TDO. You can change the weather and the opposing Pokémon.