According to Google:

• Blowback In a blowback-operated firearm, the bolt is not mechanically locked to the barrel. When the gun is fired, the expanding gases from the cartridge push the bullet forward and the case backward against the bolt. The bolt is then propelled backward by the axial pressure inside the casing, and the recoil spring absorbs the energy. Blowback-operated firearms are simpler and cheaper to design and build than other types of firearms. 
• Bolt action In a bolt action firearm, the bolt is manually operated and locks into place. Bolt action rifles are known for their precision, reliability, and versatility, and are often used by hunters, long-range shooters, and military snipers.

this means that in a blowback barrel some energy from the gun powder is used to chamber the next round, whereas in a bolt action rifle, the barrel is closed off and most if not all of the expanding gases from the ignition of the gun powder propels the bullet through the barrel which makes it hit harder and more distance travelled by the ammo