A method and apparatus are disclosed for substituting a different stock, and a forend assembly, in a long gun (e.g., a shotgun) without the use of tools by a user in the field. Applicants' preferred apparatus for substituting a stock comprises: a long gun (e.g., an illustrated shotgun) having a stock and a receiver assembly; and an adaptor which removably interconnects the stock to the receiver assembly, wherein the adaptor includes: an adaptor base bolted to the receiver assembly; and a tool-less stock release means slidably attached to the base, whereby the stock release can be lifted up by a user to release the stock from the adaptor. Upon a new stock being placed in the adaptor, the stock release means can be pushed down, back into the adaptor base, to lock the adaptor, whereupon the adaptor interconnects the substitute stock with the receiver assembly. Applicants' preferred forend assembly comprises: a modified forend carrier that is affixed to the long gun (e.g., the illustrated shotgun); and a forend which removably mounts onto the fixed carrier by a tool-less forend release means attached to the forend and carrier, wherein the tool-less forend release means comprises a tongue-and-groove arrangement and a releasable lock. This permits the forend to be swapped out.