Legally, the "main parts" of a firearm are
1. the barrel.
2. the breech:
This is the part directly closing the chamber or the barrel.
In the case of separable breeches, both the breech head and the breech carrier are essential parts.
3. the cartridge chamber, if this is not already part of the barrel.
4. the housing:
This is the component that accommodates the barrel, the trigger mechanism and the breech.If the housing is composed of an upper and a lower housing part, both parts are "main parts". For handguns (total length up to 60 cm/23.6"), the lower part of the housing is called the frame; if it is intended to accommodate the trigger mechanism, it is a "main part", too.
Semi-automatic long guns (total length over 60 cm/23.6") also often have an upper and lower housing part (upper and lower receiver, for example with M16/AR-15 style semi-auto rifles). Both parts, even separate from each other, are also "main parts" within the meaning of German weapons law then.
These "main parts" within the meaning of the law (NOT also stock, grip plates, springs and screws etc.!) are legally equal to the actual firearms, even as separate individual parts. The import and export of such "main parts" for presentation purposes at IWA OutdoorClassics is therefore subject to the same regulations as the import and export of the respective complete firearm.