The Bushmaster Carbon 15 M4 Carbine is a unique hybrid of traditional AR15 design and space age Carbon 15 materials. The upper and lower receivers of the C15M4 Type are molded of Carbon 15 composite which offers a weight savings of 3/4 of a pound compared to the standard forged aluminum receivers. In addition, these molded receivers are completely impervious to moisture, rust or corrosion and offer a 40% increase in strength over aluminum. The Carbon 15 material is the same throughout, so there is no surface finish to wear off or require maintenance.