Patent ID: 7631453

Claim:
A blowback-operated semi-automatic rifle kit comprising: a receiver; first and second bolt assemblies that are interchangeably insertable inside said receiver through an opening at a forward end of said receiver only when no barrel is coupled to said receiver; first and second barrels that are interchangeably attachable to said forward end of said receiver, said first barrel being attachable when said first bolt assembly is inside said receiver and having a first barrel length, and said second barrel being attachable when said second bolt assembly is inside said receiver and having a second barrel length greater than said first barrel length, wherein said first bolt assembly and said first barrel are for use with a first type of cartridge, but not a second type of cartridge, and said second bolt assembly and said second barrel are for use with said second type of cartridge, but not said first type of cartridge, said first bolt assembly comprising a first bolt that is driven backwards by a reaction force of the explosion inside said first cartridge during firing when said receiver, said first bolt assembly and said first barrel are assembled, and said second bolt assembly comprising a second bolt that is driven backwards by a reaction force of the explosion inside said second cartridge during firing when said receiver, said second bolt assembly and said second barrel are assembled, said first bolt having a first bolt length and said second bolt having a second bolt length less than said first bolt length.