A reader needs to carry out some culling
Can I shoot muntjac with No.3 shot?
Muntjac are deer and are therefore protected by the Deer Act which prohibits the use of any smooth-bore gun, except in very specific circumstances.
If you find a deer caught in a fence, injured by dogs or hit by a car, you could use a shotgun to end its suffering but otherwise you should use a proper deer rifle.
This means, in England and Wales at least a .240 calibre and in Scotland, where no calibre is mentioned, a bullet of at least 100 grains which effectively also means .240 minimum.