Achieving high critical current density in practical superconductors for high-field applications requires well-connected fine grains decorated with nano-scale crystalline defects to immobilize magnetic vortices. In compounds with rigid crystal lattices, however, grain refinement is usually accompanied by the release of stored strain energy rather than the retention of defects. Here, we demonstrate a scalable fluid-assisted milling strategy to produce high-purity Ba_1–xK_xFe₂As₂ precursor powders with uniform grains. Unlike dry milling that induces catastrophic fracture through breaking Fe–As covalent bonds, the liquid medium buffers impact energy and promotes shear-dominated deformation. This shear-dominated process selectively disrupts the weaker Ba–As ionic bonds, inducing a concerted lattice twist around the [001] axis and triggering the self-organization of interwoven screw dislocation networks. The dislocations with a density 2–4 orders of magnitude higher than those in conventional ceramics serve as strong pinning centers for magnetic vortices. Together with better grain connectivity and texture, the tapes fabricated from optimally milled powders exhibit a 50% enhancement in critical current density, reaching 1.45 × 10⁵ A/cm² at 4.2 K and 10 T. Our results establish fluid-assisted milling as a practical route to synergistically refine grains and construct strong pinning landscapes, offering a scalable pathway to high-performance iron-based superconductors.