Complex sentence: This energy is then transferred to the base of the bullet and to the rear of the cartridge or breech, propelling the firearm rearward into the shooter while the projectile is propelled forward down the barrel, with increasing velocity, to the muzzle.
Split into simpler sentences: This energy is then transferred to the base of the bullet and to the rear of the cartridge or breech. Then the firearm is propelled rearward into the shooter and the projectile propelled forward down the barrel; increasing in velocity to the muzzle.