As the noise may be unreasonable (after 11pm for eg) try getting in touch with your local council's Environment officer. They will get you to log the noise, and may take it further if they feel it warrants it and they are usually more effective than the police I have found. Better if all your neighbours do as well at the same time. Also a Rights of Way officer may be interested if the person is carrying or discharging a loaded firearm in a public place (or discharging within 50 feet of the centre of a right of way). Or if the person in question is using "threatening or insulting words or behaviour with intent to threaten violence". Or to point his gun at you, loaded or not comes under the Public Order Act. They may go out and speak to the landowner. Maybe worth a try
