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
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
I t works with pistol cartridges because they are relatively small and the force can be absorbed by a heavy bolt or spring or both. A magnum catride is way to powerful and you need to delay opening the breach to let the pressure escape.
I t works with pistol cartridges because they are relatively small and the force can be absorbed by a heavy bolt or spring or both. A magnum catride is way to powerful and you need to delay opening the breach to let the pressure escape.
As the amount of propellant increases in explosive capacity, the heavier the bolt needs to be to soak up the energy and have it move slow enough that it doesn’t shoot out the back of the weapon. At some point you’re going to need huge bolts and that’s damn near impossible to control.
That’s why the biggest caliber rounds seen on blowback firearms are pistol ones, 9mm Parabellum, 10mm/.40, and .45ACP.
Bigger than that, such as rifle caliber rounds, are too unwieldy and not safe for practical purposes. The solution which most firearms have utilized for over a century is delaying the energy of the explosion in the chamber and out the barrel until it’s just enough for the bolt to go back and forth, clearing the spent case and cycling the next round as it does. To delay the movement of the bolt there are many designs, from roller delayed on the HK MP5, to gas or piston driven like the AR-15 and HK 416 where some of the gas going out the barrel gets in a small channel that forces a mechanism to rotate the bolt out of a locked position. I recommend Forgotten Weapons YouTube channel to check out how those systems work. From a purely mechanical aspect it’s quite fascinating.
As the amount of propellant increases in explosive capacity, the heavier the bolt needs to be to soak up the energy and have it move slow enough that it doesn’t shoot out the back of the weapon. At some point you’re going to need huge bolts and that’s damn near impossible to control.
That’s why the biggest caliber rounds seen on blowback firearms are pistol ones, 9mm Parabellum, 10mm/.40, and .45ACP.
Bigger than that, such as rifle caliber rounds, are too unwieldy and not safe for practical purposes. The solution which most firearms have utilized for over a century is delaying the energy of the explosion in the chamber and out the barrel until it’s just enough for the bolt to go back and forth, clearing the spent case and cycling the next round as it does. To delay the movement of the bolt there are many designs, from roller delayed on the HK MP5, to gas or piston driven like the AR-15 and HK 416 where some of the gas going out the barrel gets in a small channel that forces a mechanism to rotate the bolt out of a locked position. I recommend Forgotten Weapons YouTube channel to check out how those systems work. From a purely mechanical aspect it’s quite fascinating.
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Rifles and powerful pistols have a similar problem. If a powerful charge ignites and pushes he case backwards fast enough, some of the blast will come out the ejection port.
Also, not only is it dangerous to have some of the blast come out near your face, you also want all of the blast applying it’s force to the bullet, instead of wasting some of it out the ejection port.
You must “delay” the unlocking of the bolt. There are many ways to accomplish this.
A simple blowback pistol is very affordable to make, but once you scale it up to a more powerful cartridge, you begin having problems, and you must switch to a design that delays the unlocking of the bolt, but…still “soon enough” that a tiny amount of pressure remains in the barrel to still push the case and bolt backwards.
It is a delicate balance in the design.
Rifles and powerful pistols have a similar problem. If a powerful charge ignites and pushes he case backwards fast enough, some of the blast will come out the ejection port.
Also, not only is it dangerous to have some of the blast come out near your face, you also want all of the blast applying it’s force to the bullet, instead of wasting some of it out the ejection port.
You must “delay” the unlocking of the bolt. There are many ways to accomplish this.
A simple blowback pistol is very affordable to make, but once you scale it up to a more powerful cartridge, you begin having problems, and you must switch to a design that delays the unlocking of the bolt, but…still “soon enough” that a tiny amount of pressure remains in the barrel to still push the case and bolt backwards.
It is a delicate balance in the design.
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