Complex sentence: Sabot systems result in smaller decreases in recoil (which is proportional to momentum) compared to a full-size projectile, they allow an increase in projectile velocity per unit of barrel length.
Split into simpler sentences: Sabot systems result in smaller decreases in recoil (which is proportional to momentum). Compared to a full-size projectile, they allow an increase in projectile velocity per unit of barrel length.