nice model, but it's not the biggest artilery piece in the world...
meet "Dora"
This monster of a gun fired 80cm rounds, which means it had a bore of 31.5 inches. It took two tonnes of propellant charge to send one the big 7 tonne shells twenty-nine miles.
It was mounted on no less than 40 railway axles and weighed in at over four hundred tonnes. It had to be dismantled to move, which took two thousand men to accomplish. The mere task of aiming, firing and reloading this single gun took 500 men.
This gun was designed specifically to breach the French "Maginot Line" underground bunkers and "popup" gun turrets, which ran from Belgium to Switzerland. Hitler ordered 3 of them, but got impatient and started World War 2 before they were completed. Without his big guns to cut through the Maginot Line, The only option Hitler had was ignore the neutrality of Holland and Belgium. His armies cut through them, bypassing the dreaded forts, and for the second time in just 21 years half of France lay in German hands.
Only 2 of these big guns were ever built, with half the parts complete for a third.
Anyways, Big Bertha had the longest range of any artillery piece ever made, and proved it by bombarding Paris from some 58 miles away...