slide lock

I’ve a gen4 G34, the slide doesn’t lock back after the last round. - thoroughly disassembled & ultrasonically cleaned - 124g handloads with 7.0g of AA7 or 147g Win white box. - 2 new gen5, 1 gen4 and a Magpul mag. - When the slide’s pulled back it’ll lock. Slide release spring weak? Other...