A deactivated weapon would have started life as a service or commercially issued weapon be it a rifle, pistol, sub machine gun, light machine gun, mortar, missile or hand grenade, which for some reason or another has been taken out of service or in most cases has become obsolete for use.
For a weapon to become deactivated it needs to have most of its major components, mostly load pressure bearing parts either removed or cut away/weakened leaving the external appearance unaltered. IT CAN NO LONGER FIRE LIVE AMMUNITION.
For example: a bolt action rifle - a manually operated weapon would have to have the barrel slotted down the middle all the way up to the breech, this operation would all so remove the feed ramp, then a hardened case steel pin is inserted in the breech to stop any round (bullet) from being loaded.
In some cases once the barrel as been slotted a steel rod would be inserted down the length of the barrel and then welded in place, but leaving at least 1-2 inches clear from the front end of the barrel or other wise known as the muzzle clear (for external appearance only).
The bolt face would have to be cut back to at least a 45 degree angle to stop any ammunition being loaded. And various parts of the receiver would also be slotted or cut so that the frame will not take any firing force thus weakening the receiver.
This operation is carried out on all types of weapons, pistols, self loading/automatic rifles, sub machine guns and larger machine guns although slightly different cuts and parts weakened were made.
Once this work has been carried out, the weapons would be taken to the local Proof House for inspection.
A proof house is a place where guns and barrels fitted to guns get proofed tested under load in firing conditions, they look for signs of weakness in manufacturing making sure the weapon and the fitted barrels work correctly as they should do without malfunctions.
There are only two Gun Proof houses in England that specialize in this sort of work one is in Birmingham that use the crossed swords proof stamp and the other is in London that use the crossed sabre stamp.
Any deactivated weapon that goes to either of the proof houses, an inspector would have to inspect the weapon and make sure the weapon has been deactivated to the current standards of the time making sure it is incapable of firing any missile, bullet or any other object from its barrel and that all the major functional parts have been rendered incapable and no longer serve there original manufactured purpose.
Once this type of inspection has been carried out, the inspector will then stamp the parts of the weapon with an inspector stamp which proves the weapon has been deactivated and is incapable of firing anything.
Each deactivated weapon will come with its own certificate of deactivation, which should be kept safe at all times as it proves the weapon has been deactivated and inspected by the proof master. Other brief infomation to check will include the date and year of the deactivation, who it was submitted by, serial number off the gun, so it matches the gun correctly and barrel length.
Old specification refers to any weapons that were deactivated before October 1995. These types of guns will all have full moving parts and can be stripped down, any Weapons deactivated after October 1995 are known as new specification deactivated weapons and will not have full moving parts and will not be able to strip down.
Old specification deactivations allowed for all weapons to have working actions, which could be fully stripped down to their major components.
Revolvers were allowed to have unblocked cylinders enabling inert ammunition. Under new specification rules, this could no longer be done.
Post 1995 to 2016 specification rules, all weapons had all their actions welded prohibiting cocking or dry firing and stripping down. In 2016-2018 the deactivation rules were changed allowing certain weapons (assualt rifles sub machine guns mostly) to have some moving parts, including triggers, safety levers and either 'dummy bolts' fitted or parts of the original bolts to move again but still not being able to cock dry fire or strip down.