Barrel construction, metallurgy, and tapering set harder limits than the quenching process alone. The discussion treats 42 calibres as roughly the shortest useful barrel and 45 calibres as the preferred length. A barrel that droops compromises rifling alignment, accuracy, and range. If a faulty shell detonates inside it, the damage can cost the barrel and may reach the turret. These risks make nine 18-inch guns more plausible than six 20-inch guns. A 20-inch weapon remained a development project awaiting a metallurgical and gun-science breakthrough rather than a proven design held back by factory equipment.
Chapter · 11:04-16:25
Barrel droop makes extreme-calibre guns a metallurgical problem
The core constraint on a very large naval gun is making a long barrel that retains its shape, accuracy, and safety under firing loads.