Reliable, infallible, sturdy or error-tolerant.
Unbreakable, very tough.
Capable of withstanding a direct shot by a bullet fired from a gun.
to make resistant to failure.
To make proof against bullets.
Inflexible or without exception.
Made of cast iron.
Durable; tough; resilient.
A hard and brittle, but strong, alloy of iron, carbon, and silicon, formed by casting in a mould.