- In blowback systems, the bolt is not locked when the gun is fired. This is the defining characteristic of all blowback systems.
- All blowback systems use some of the gas generated when the cartridge is fired, to operate their mechanisms.
- All blowback systems use the empty cartridge case as a sort of piston to operate their mechanisms.
- The main problem to overcome on blowback systems is how to prevent the breech from opening the instant the gun is fired. The breech should only begin to open after the bullet has left the front of the gun and gas pressure in the chamber has dropped to a safe level. All blowback systems have different ways of overcoming this problem. Some use inertia, others use the principles of levers, still others use friction, gas etc.
So what are the advantages and disadvantages of such systems?
- Blowback systems have fewer moving parts than other systems.
- In most cases, there is no gas tube hanging off of one side of the barrel and affecting the natural harmonics of the barrel. This allows the barrel to be free-floated.
- Generally reliable provided they are used with the ammo that they are designed for.
- Relatively cheaper to manufacture.
- Some blowback systems offer recoil reduction and less muzzle climb when firing rapidly.
- Cannot be used with powerful cartridges. These are generally suited to low-powered or medium-powered weapons at most. This is why most blowback weapons are pistols or submachine guns, not high powered rifles.
- Some actions (such as straight blowback) make the gun heavier by the nature of how they work.
- Some blowback actions are extremely sensitive to the type of cartridge used. While they are reliable when used with the cartridge that they're designed for, slight variations (such as the weight or the material of the case) can cause problems. Unlike a gas operated system which has a user-tunable gas regulator, these cannot be tuned to different cartridges.
- Some blowback systems quickly get dirty with use.
Blowback systems are generally most prevalent in smaller pistols and submachine guns, because they cannot reliably handle higher powered cartridges.