Training rifle and magazine

A polymer training rifle comprising:

• an inert modular barrel having a proximal end, a distal end, and a first longitudinal axis extending from the proximal end to the distal end, which comprises
• a barrel extension segment adjacent the proximal end which comprises,
• a tapered cylindrical portion aligned with the first longitudinal axis, and
• a projection extending from the tapered cylindrical portion which comprises,
• a first slot aligned with the first longitudinal axis,
• a second slot perpendicular to the first slot, the second slot intersecting the first slot, and
• a fastener attachment member which comprises a threaded opening such that the fastener attachment member is disposed in the second slot and the threaded opening is aligned with the first slot, and
• a modular receiver having a front end and a rear end which comprises,
• a barrel attachment site on the front end which comprises,
• a rim which defines a first projection, and
• an opening extending from the first projection into the modular receiver, such that the opening defines a socket for receiving the barrel extension segment, which comprises,
• an upper end wall,
• a lower end wall, and
• a surface connecting the upper end wall to the lower end wall,
• a receiver extension tube attachment site on the rear end of the modular receiver which comprises a threaded cylindrical bore extending from the rear end into the modular receiver,
• a cavity within the modular receiver, the cavity being situated between the threaded cylindrical bore and an interior end wall that is spaced from the socket, and
• a passage extending from the interior end wall to the upper end wall, and
• a fastener which comprises a head and an elongated body such that the elongated body is disposed in the passage and a portion of the elongated body mates with the threaded opening of the fastener attachment member to fix the barrel extension segment within the socket.