bolt not locking back on last shot

[terrywick4]

This is on my 24 " satern barrel Using factory Hornady 123 A-Max, Have tried, 3 different bolt carriers, two different bolts, 10 different mags (mix between 5,10 17 and 25 rounders), 3 different buffers (standard carbine buffer, H2 and H3), two different lowers (maybe a third) no add ons to the bolt release. Everyother operation of this guns runs flawless. Is wierd because with an empty magazine I can pull the bolt back and it will lock by itself.