The weapon uses 4.73×33mm caseless ammunition, with the propellant shaped into cuboid blocks. The ammunition has also been designated as 4.92mm because for the HK G11 ACR, a variant developed for US Military trials, the US convention of groove to groove measurements of the bore was employed, rather than land-land. The projectile is 4.93 mm in diameter with a case length of 33 mm, the US case length measurement is 34 mm since for the ACR trials the chamber length, not the actual case length was used. The 4.73 mm round is half the weight and 40% the size by volume of the 5.56×45mm NATO round. The round was designed to the same ballistics requirement as the 5.56×45mm NATO round as outlined in "Evaluation Procedures for Future NATO Weapons Systems" (Document 14). However, the 4.73mm is much less likely to tumble when hitting or penetrating a soft target, and thus not as lethal. The effect on soft targets is in accordance with international conventions. Even at short ranges the round does not fragment in the soft target medium. This was confirmed in tests with gelatine.(See terminal ballistics)