Shooting wild boar
You do not tell me what calibre rifle you use and also I must point out that your firearms certificate must be amended to cover use against wild boar.
However, a specialised Continental calibre such as a 9.3x74R with a 270-grain bullet travelling at 2,300fps and delivering 3,172ft/lb energy can be effective, though a .30-06 with a 200-grain bullet would also work well.
If you only want a dedicated boar gun, a 9.3x62mm is excellent, shooting a 285-grain bullet at 2,200fps and giving 3,063ft/lb energy, or even a .35 Whelen, a necked-up .30-06 case to .35 calibre, is one that makes a good red deer cartridge.
The minimum calibre you can use with a bolt-action rifle is something such as a .270 Win, using heavier bullets with a strong construction, such as Partitions.
A rifle in .308 or .30-06 can be excellent for these animals but as with any other game you must place the bullet in the right place for a humane shot.
If you are using a high seat rather than driving, you can take a better, well-aimed shot and even a 6.5x 55mm with a 156-grain bullet will do the job.
If you have a .308 then this can double as a deer rifle.