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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Firearm design is a battle of engineering vs forces. The explosives are stored in relatively weak brass cases that must be entirely enclosed within the foreign chamber or they explode sideways. So most of the engineering is about making sure all the pressure is gone before you remove the brass. With blowback the low power rounds can’t push back very hard and pressures are lower but even then lots of mechanisms are deployed to delay the movement of the bolt to make sure the stresses are contained, but by design this requires that the breach face (the back face of the foreign chamber) and the break walls and barrel are not mechanically locked together.
For safety with high power rounds you want big metal lugs to hold the breach closed so that it can’t let gasses out the wrong way, in the first rifles this action was mechanical, you’d lift the bolt handle which rotates the breach face to unlock it, pull back to eject and then close again and lock again with a twist. The gas operated system just automated this process with the added advantage that you can delay the action by placing the gas port further down the barrel, add restrictors or modify the amount of gas extracted so you can be sure all the burning has happened and the round has left the batrel before you open the breach and let the brass out. The only thing that keeps a breach closed with blowback is inertia which means for high powered guns you need lots of mass. So a heavy gun. Gas does the same job much lighter
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