I’m not super familiar with firearms and usually only see them in video games. I notice that pistols and sub machine guns use something called blowback to load the next round from the magazine. My understanding is that the recoil of the round pushes the bolt back and ejects the bullet. This works for pistols and submachine guns like a Glock or MP40.
For rifles though, they have to be gas operated or put in a separate tube so that the gas can go backwards to push the bolt back. Why is this the case? Why can’t rifles like the M16 or AK47 simply use blowback and let the recoil of the gun push the bolt back and load the new round?
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Blowback firearms usually have a short barrel, because, in effect, the bullet in the barrel *IS* the gas system for the firearm. However, as the chamber pressures increase, and the barrel gets longer, this ceases to be practical, and a pure blowback system would shift the bolt and bolt carrier out of battery long before the bullet had exited the barrel. The result would be that a great deal of the energy in the cartridge would blow out the back of the firearm, instead of propelling the bullet towards its intended target.
This is why the gas taps are near the end of the barrel. Before the bullet clears that point, it seals off the expandind propellant gasses behind it. Once the bullet passes, the gasses pressurize the gas tube, and cycle the action.
You *can* find recoil-operated firearms with long barrels, however, one example is the 50 caliber M2 Browning, the ‘Ma Deuce’. You will notice that it has an *enormous* bolt/bolt carrier, which gives it enough intertia to prevent premature ejection of the cartridge after firing. This would make recoil-operated rifles very bulky, and every pound of gun you’re carrying takes away from the pounds of food, ammunition, and other equipment you’re carrying.
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