While artillery traditionally has been limited to a maximum range of 20-30 km, recent years have seen the introduction of new systems that support a maximum range of more than 40 km. In February 2013, Nammo started to develop a new family of conventional 155 mm artillery ammunition, specially designed for long range. The new shell design is known as the 155 mm IM HE-ER (Insensitive Munitions, High Explosive, Extended Range). It provides artillery forces with the ability to effectively target both personnel and vehicles at ranges over 40 km with very good accuracy – and it does so without adding any guidance systems or submunitions. Instead, Nammo has drawn on its experience from two other areas of expertise – rocket motors and sniper ammunition – to design one of the most capable conventional shells on the market.
Nammo is marketing its 155 mm IM HE-ER projectiles with an interchangeable base bleed (BB) unit or a hollow base (HB) unit. It can be fired from 155 mm 39- and 52-calibre towed and self-propelled artillery weapons whose ordnance meet the NATO Joint Ballistic Memorandum of Understanding (JBMOU). The 155 mm IM HE-ER projectiles are complemented by illuminating, smoke, and practice projectiles, which also have interchangeable BB or HB units. The 155 mm illuminating projectile is available in two versions: white light and infrared (IR), with the former lasting 60 seconds and the latter 90 seconds. The 155 mm illuminating contains three red phosphorous canisters that have brake flaps, which are claimed to make them effective in deep snow and marsh. The 155 mm training projectile has been qualified and is available in two versions: inert with no energetics or a small explosive spotting charge.
In 2016 Nammo reached a significant milestone in the development program when the 155 mm IM HE-ER completed its qualification trials. The test was a demonstration for the Swedish Armed Forces, and the rounds were fired from the Swedish Archer Gun System. A total of 32 live rounds were fired, all functioned as intended with a low dispersion in the target â€“ High Precision at Long Distance. This followed an extensive test program that included environmental, transportation and firing tests. Such testing is a complex and rigorous process, and requires access to highly specialized test areas. During the maximum range test, when fired over the important benchmark range of 40 km at sea level, parts of the airspace over southern Sweden had to be closed off as the shells reached over 16 000 meters (more than 50 000 feet) into the air in less than a minute. By comparison, most airliners fly at altitudes between 30 and 40 000 feet.
Nammo experience from rocket motors has allowed us to fit the shell with a small rocket motor known as a base bleed. A base bleed is essentially a small rocket installed at the base of a shell that is ignited when it is fired. As it burns, the base stabilizes the airflow over the projectile, reducing drag, and thereby adding range. Nammo is today one of the world’s leading providers of rocket motors for anti-air missiles, including the AMRAAM, the AIM-9X Sidewinder, and the ESSM, and we have used this experience to also become the largest manufacturer of base bleeds for ammunition. Nammo experience from sniper ammunition has also benefited the design of the new shell, as high-performance sniper ammunition faces many of the challenges as long-range artillery ammunition. When firing at extended distances both suffer from the fact that even extremely small variations in materials and shape can change the airflow and weight distribution of the projectile, affecting what is known as its ‘ballistic properties’.