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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In a straight blowback gun all the recoil forces will be transfered to the bolt. So the bolt gets propelled very fast backwards against the main spring and eventuall crash into the rear of the receiver. If the bolt goes too fast it is going to break stuff. Maybe not right away but it is going to weaken the receiver and eventually crack it. The MP40 only gets away with it because the bolt is very heavy so it does not get much speed. The modern MP5 is very comparable using the same ammunition and same muzzle energy but is much lighter because it use a lighter bolt with a roller delay mechanism. So most of the recoil energy is transfered into the trunion and then receiver as the powder is burning and only some of the recoil energy is used to accelerate the bolt backwards.
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