Evaluating the recommended safety distance of a recoil booster

After a supplier course for the FN MINIMI 7.62 mm Tactical machine gun, it was noted that the accompanying recoil booster FN Herstal S. A. B0897 has a hole going through it, which is parallel to the line of fire. The hole has been identified as a potential safety hazard during training with blank ammunition, because if a foreign object (e.g. a small stone) gets stuck inside the hole it might be pushed out by the gas like a projectile. The Norwegian Defence Research Establishment (FFI) have investigated this potential safety hazard experimentally. By firing realistic improvised ammunition such as sticks, stones and ice towards a skin simulant, we observe dangerous perforations in the simulant. At two meters, the branches, ice and stones could reach velocities between 140 − 520m/s, 110 − 260m/s, and 715 − 800m/s respectively.