0.25 gram BBs are an alternative weight of BBs offered and are generally recommended for airsoft guns between the 350-420 FPS range. In keeping with the requirements of an airsoft gun, they will all be 6mm round plastic BB pellets. At least 5 grams heavier than 0.20g BB's, their extra weight allows the BB to travel farther thanks to the increase of momentum. Still a balanced weight of BB, they are produced with an optimal density that makes their size to weight ratio to be the most capable BB's allowing them to work for a variety of scenarios and guns. Where lighter BB's would shatter upon contact when asserted by a force over 300 FPS, 0.25g BB's will maintain its structure and flight pattern (your accuracy) up to 420 FPS. In FPS ranges beyond 420 FPS, 0.25g BB's will continue to maintain its structure however its flight pattern will be more erratic due to increased air resistance.