PARIS — KNDS, the French-German maker of the Leopard tank and the Caesar truck-mounted gun, pitched a new howitzer with a barrel longer than any NATO production artillery, which the company said gives the weapon a range of up to 60 kilometers (37 miles) with standard high-explosive shells. The howitzer uses KNDS Germany’s Artillery Gun Module mounted on a tracked Boxer chassis and fitted with a French barrel. The company has already fired a prototype of the gun, and aims for serial production