The calculated distance (air line) between Blackrock and An Muileann gCearr is approximately 50 miles respectively 81 kilometers.
By car or train, the actual journey to An Muileann gCearr is certainly longer, as only the direct route (as the crow flies) between Blackrock and An Muileann gCearr has been calculated here.
Air line (approximately)
81 kilometers
44 nautical miles