Rogue Fitness has a smashing power training tool that is all bulk. The Rogue “SISU” War Hammer is seven gauge steel with benefits, as variable weight can be inserted into the head of the hammer. Filled with lead shot you have a maximum 28 pounds (empty weight 14lb, weight with sand 20lb) of muscle driven determination.
The handle is a bit longer than a traditional sledgehammer, being 38″ to the head, but this provides greater leverage and force. The square head requires the development of control to offset rebounding from a glancing blow. The War Hammer is nigh on to indestructible so you can go full-on Viking with your training sessions. Details in the video