The risk if caught smuggling it is likely they would not allow you to travel with it and possibly report you to the police, which may result in you no longer being a fit and proper person to keep firearms.
Tunnel.
Personal vehicle
3.1.2
Firearms: the Carriage of Firearms is RESTRICTED. Firearms (including sporting weapons) are not permitted for Carriage unless accompanied by a valid firearms or shotgun certificate(s) corresponding to the weapon(s) carried.Firearms must be declared to LeShuttle staff at check-in, and/or as otherwise directed.
Before Carriage, Firearms must be disabled by removing the bolt, magazine or other vital operating part. Such parts must be kept separate from the firearms and concealed from view. Firearms and parts must be stored securely at all times.
3.1.3
Ammunition: The Carriage of ammunition is
RESTRICTED. The quantity of ammunition carried must be kept to a minimum. Ammunition must be stored securely and separately from any firearm and concealed from view.
3.1.4
Explosives: The Carriage of explosives is
PROHIBITED.
3.1.5
Weapons: The Carriage of weapons of any kind is
RESTRICTED.
3.2 Any Vehicle carrying Firearms, ammunition, explosives or weapons must be presented for a security check in accordance with the Channel Tunnel Security Order 1994. LeShuttle reserves the right to refuse Carriage to any Vehicle that may in LeShuttle's sole opinion, present a risk to the health, safety or security of other passengers, staff or Shuttle operations.
3.3 Further information relating to the Carriage of Hazardous Articles is available on LeShuttle's website.
Legal information about the carriage of dangerous and hazardous goods and substances.
www.leshuttle.com
Then this is commercial freight regulations, as you see only 15kg NEQ of 1.4s
P&O
DFDS
section 12
DFDS may accept vehicles carrying Hunting and Sporting weapons or ammunition under certain controlled conditions. You must declare the carriage of firearms, weapons and ammunition and provide proof of legality for their carriage by disclosing the type of license/certificate held if applicable. This must be done at the booking stage. To comply with strict compliance and conditions, passengers must fill out the
Notification of Carriage of Weapons/Ammunition Code 100 form at least 24 hours before travel, this can be provided at the booking stage by contacting us direct. Please also note the import regulations of the respective country.
For more information regarding carrying dangerous goods, please see section 12 in our Terms and Conditions
So nothing other than ammunition and limited quantities.