autoloading gun construction having the breach end of a barrel removably assembled to the forward end of a barrel extension which is positioned between and secured to wall sections of two opposing receiver plates of a receiver section the improvement comprising an aperture formed thru each wall section and a weld formed between edge portions of each aperture and adjacent portions of the barrel extension application_number US 64873303 A description referring to the drawings and with particular reference to the claims herein the present construction modifies the connection means between a barrel extension such as item 120 and a barrel such as 40 and also receiver sides such as items plates 117 l and 117 r of the aforesaid u s pat no 4 693 170 as shown in fig2 13 and 31 thereof in said patent the connection is made between all three of these structures by four rivets 118 which are headed over clinched on the outside of plates 117 l and 117 r in this construction shown particularly in applicants 39 fig6 taken from fig3 of said patent and wherein additional new numbering is added where necessary for clarity starting at 500 rivets 118 tightly nest in transverse grooves 500 across the top and bottom of the inner end breech end of barrel 40 and thereby fix the barrel to extension 120 and thus to receiver section 41 this structure of course prevents removal of the barrel which can cause great inconvenience where it is desired to replace a damaged barrel or to replace the barrel with another type e g from shotgun to rifle referring to the present drawings wherein the numbering of parts where relevant is the same.