First of all, before raising a rifle to a wild boar, you must ensure your firearms certificate specifies you are allowed to shoot these animals.
As far as rifle calibres are concerned, wild boar are powerful, strong and potentially dangerous animals that must be treated with respect.
A 200lb boar has an extremely tough, thick skin and powerful bones, and demands a calibre which will ensure a killing shot.
There have been reports of calibres as small as .22 centrefires being used against wild boar, but these, and even .243 Winchester calibre rifles, are inadequate and should never be contemplated.
The result will usually be a wounded animal which may die a lingering death or prove extremely dangerous.
The minimum calibre to be used against wild boar is the .270 Win, delivering a muzzle energy of 2,700ft/lb, but it is recommended that a calibre of no less than 7mm with a bullet of 160 grains-plus and muzzle energy of no less than 2,800ft/lb should be used.