Ball bearings do not have welding/cast lines. It would spoil their function.
According to the position of Pride and his daughter the explosion would be in the garden outside.
When explaining the explosive device, on multiple occasions the characters describe it as "ammonium nitrate and fuel oil" as if no one has ever head of "ANFO", the most common descriptor, or even Timothy McVeigh. And none of the other characters act as if they are familiar.