Complex sentence: Micro-caliber (less than 5 millimeters) ammunition wished to achieve high velocity, flat trajectory and good penetration in automatic weapon, and with low recoil, but the tiny size of the bullet required a simple blowback operation style rather than more complex forms of operation.
Split into simpler sentences: Micro-caliber (less than five millimeters) ammunition makers wished to achieve high velocity, flat trajectory and good penetration in automatic weapons, and with low recoil. The tiny size of the bullet required a simple blowback operation style rather than a more complex form of operation.