The X01 features an upper/lower receiver construction that attaches via the forward receiver hinge and is locked in place by a rear recoil spring guide. Models equipped with a dual-rod buttstock or arm brace will also lock together via two guide rod channels that span both the upper and lower receiver for added stability. The upper receiver features shell deflection ramps to mitigate malfunctions. Steps to clear a malfunction are identical to the P320 with the exception of working the action via the charging handle rather than the slide itself. The upper receiver was designed to accommodate suppressor iron sights.