Quick answer: Unreal BSP brush converted to a Static Mesh but physics still uses the old box collision? The mesh asset needs new collision generated — static mesh editor → Collision → Auto Convex.

Block-out geometry converted from BSP gets the converted static mesh but bullet traces still hit the original AABB bounds.

Generate New Collision

Open the Static Mesh asset. Collision menu → Auto Convex Collision (with sane settings) or Use Complex Collision As Simple. Old box collision replaced.

Use Complex As Simple

For non-deformable static meshes, this is the simplest path. Performance penalty for complex shapes; fine for backgrounds and large props.

Convex Decomposition

For physics-interactive meshes, generate convex hulls. Tune hull count vs accuracy in the dialog.

Block-out vs Final Mesh

BSP block-outs are temporary. Replace with proper meshes early; collision conversion is a one-time chore that scales poorly across hundreds of brushes.

Verifying

Physics queries hit the actual mesh geometry, not the old AABB. Bullets, gravity, character collision all behave correctly.

“Converted brushes need new collision. Auto Convex or Complex As Simple from the mesh editor.”

Use BSP only for the initial block-out — replace with art-pipeline meshes by the time gameplay tuning starts.