US Patent 8464453 Blowback bolt upper receiver and barrel assembly

Disclosed herein is a modified upper receiver assembly, which in one form is operatively configured to be fitted to a conventional lower receiver of a rifle so the user can use their normal lower receiver having a pistol grip, trigger assembly and butt stock. The upper receiver is configured to provide a blowback bolt assembly of larger mass than would be possible with similar density materials of a bolt fitted within an upper receiver conventionally made for said lower receiver.