High strength upper receiver system and method for modular rifle

A modular rifle system comprising:

• a lower receiver assembly;
• an upper receiver assembly having a first portion and a second portion;
• and
• a barrel assembly, consisting of a barrel and a barrel nut connector sleeve;
• and
• an upper receiver liner insert within the first portion of the upper receiver assembly;
• the upper receiver liner insert secured within the first portion of the upper receiver assembly, the barrel assembly attached to the liner insert, a second portion of the upper receiver assembly attached to the first portion of the upper receiver assembly, and the upper and lower receiver assemblies coupled.

A method of strengthening an upper receiver of a modular rifle system having an upper receiver assembly and a removable barrel assembly, comprising the steps of:

• inserting a liner insert within a first portion of the upper receiver assembly
• securing the liner insert within the first portion of the upper receiver assembly by engaging screw threads on the liner insert with receiving threads within the first portion of the upper receiver assembly;
• further securing the liner insert within the first portion of the upper receiver assembly by insertion of anchoring devices into the first portion of the upper receiver assembly;
• attaching the barrel assembly to the liner insert;
• and
• attaching a second portion of the upper receiver assembly to the first portion of the upper receiver assembly.