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?
In: 26
It’s an issue of inertia and pressure. In a blowback firearm, the inertia of the bolt needs to keep the case chambered long enough for the pressure to drop to a safe level before extraction. With pistol cartridges like 9×19, that’s relatively easy to do, and the bolts don’t need to be too heavy, usually no more than a pound at most. With rifle cartridges, it becomes more difficult. You are dealing with higher pressures, and heavy bullets moving at several times the speed. In order to keep the case chambered for a cartridge like .30-06, for example, you would need a bolt that weighs several pounds, combined with a very heavy recoil spring. As it turns out, this can be done (see: Thompson Auto Rifle), but the result is a heavy gun with heavy recoil due to the mass of the bolt moving backwards. In the case of the Thompson Auto Rifle, the bolt velocity was so high that spent casings were being embedded in the ceiling of the shooting range they tested it at, since the pressure of .30-06 was so high that it would begin to move the bolt backwards before the pressure had dropped to a safe level, resulting in very high bolt and extraction velocities.
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