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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They do have rifles that use these, Spanish Cetme and it’s upgraded clone the HK G3 series do this. I am no expert and anybody who is that sees anything wrong with my explanation feel free to correct me. Rifles calibers have a lot more chamber pressure than pistol calibers which attributes to the projectile leaving the muzzle at higher speeds. This means your bolt has significantly more pressure on it when firing which means it will move back at a higher speed unless you bleed off some of that pressure first. barrels are intended to funnel all the gas out the muzzle end to impart as much force on the bullet as possible to raise the speed of the bullet. If the bolt opens prior to the bullet leaving the barrel gas can now go the opposite direction and your bullets velocity will be impacted. Guns like the HK G3 use rollers which are designed to delay the bolt from moving backwards until after the bullet has left the barrel which allows for some of the pressure to be released prior to the bolt unlocking which allows for less force on the bolt and the most efficient velocity for the bullet. Rifles with gas or piston systems funnel gas further down the barrel allowing for the bullet to leave the muzzle by the time the gas/piston causes the bolt to release. Ultimately it seems that piston or direct impingement systems are easier to get dialed in than delaying the bolt moving through mechanical parts.
They do have rifles that use these, Spanish Cetme and it’s upgraded clone the HK G3 series do this. I am no expert and anybody who is that sees anything wrong with my explanation feel free to correct me. Rifles calibers have a lot more chamber pressure than pistol calibers which attributes to the projectile leaving the muzzle at higher speeds. This means your bolt has significantly more pressure on it when firing which means it will move back at a higher speed unless you bleed off some of that pressure first. barrels are intended to funnel all the gas out the muzzle end to impart as much force on the bullet as possible to raise the speed of the bullet. If the bolt opens prior to the bullet leaving the barrel gas can now go the opposite direction and your bullets velocity will be impacted. Guns like the HK G3 use rollers which are designed to delay the bolt from moving backwards until after the bullet has left the barrel which allows for some of the pressure to be released prior to the bolt unlocking which allows for less force on the bolt and the most efficient velocity for the bullet. Rifles with gas or piston systems funnel gas further down the barrel allowing for the bullet to leave the muzzle by the time the gas/piston causes the bolt to release. Ultimately it seems that piston or direct impingement systems are easier to get dialed in than delaying the bolt moving through mechanical parts.
I’m seeing a lot of convoluted answers here. To explain it to a 5 year-old, it’s best to say that rifle cartridges have a lot more energy than pistol rounds when they are fired. Enough energy to damage the internal components of the gun. For this reason, many automatic rifles let some of that energy from the exploding powder dissipate before collecting it in a separate tube closer to the muzzle.
You can make a blowback rifle but it has a lot of draw backs compared to gas systems.
I’m seeing a lot of convoluted answers here. To explain it to a 5 year-old, it’s best to say that rifle cartridges have a lot more energy than pistol rounds when they are fired. Enough energy to damage the internal components of the gun. For this reason, many automatic rifles let some of that energy from the exploding powder dissipate before collecting it in a separate tube closer to the muzzle.
You can make a blowback rifle but it has a lot of draw backs compared to gas systems.
A blowback automatic firearm using typical rifle rounds tends to want to beat the shit out of itself and the user. Or it needs the bolt to be very heavy, which causes other issues like less controllability (that back and forth momentum transfers to the rifle), a heavier firearm, etc.
This tends to be less of an issue with pistol caliber firearms due to them having significantly less muzzle energy. Not to mention that many submachine guns throughout history that were straight blowback had lower cost of manufacturing and ease of repair as primary drivers for that decision.
You can account for these drawbacks with other engineering solutions, but the simplest solution is often to use another form of action to move the bolt whereas some of the energy is dissipated first vs straight blowback.
A blowback automatic firearm using typical rifle rounds tends to want to beat the shit out of itself and the user. Or it needs the bolt to be very heavy, which causes other issues like less controllability (that back and forth momentum transfers to the rifle), a heavier firearm, etc.
This tends to be less of an issue with pistol caliber firearms due to them having significantly less muzzle energy. Not to mention that many submachine guns throughout history that were straight blowback had lower cost of manufacturing and ease of repair as primary drivers for that decision.
You can account for these drawbacks with other engineering solutions, but the simplest solution is often to use another form of action to move the bolt whereas some of the energy is dissipated first vs straight blowback.
The principle is called Recoil operation. In pistol calibre weapons this can be simple blowback, but for larger rounds some form of delay mechanism is required.
The issue is Chamber pressure, when a bullet is fired Burning gasses expand from the bullet case and push the Projectile up the barrel, Recoil does not begin until the projectile leaves the barrel, in an ideal system the pressure from the expanding gasses should reach its maximum just before the projectile leaves the weapon,
A 9 X 19 mm round has 560J of energy, so the Bolt and spring only have to be heavy enough to keep that pressure back until the recoil happens.
.308 rifle rounds have 3600J of energy this would require a very heavy bolt and spring, so a method is required to make sure the breach (that’s the bit where the explosion starts) remains closed until the bullet leaves the barrel and pressure drops, some of the methods for keeping the breach locked are Toggles, Rollers, Flaps, Tilting block.
The principle is called Recoil operation. In pistol calibre weapons this can be simple blowback, but for larger rounds some form of delay mechanism is required.
The issue is Chamber pressure, when a bullet is fired Burning gasses expand from the bullet case and push the Projectile up the barrel, Recoil does not begin until the projectile leaves the barrel, in an ideal system the pressure from the expanding gasses should reach its maximum just before the projectile leaves the weapon,
A 9 X 19 mm round has 560J of energy, so the Bolt and spring only have to be heavy enough to keep that pressure back until the recoil happens.
.308 rifle rounds have 3600J of energy this would require a very heavy bolt and spring, so a method is required to make sure the breach (that’s the bit where the explosion starts) remains closed until the bullet leaves the barrel and pressure drops, some of the methods for keeping the breach locked are Toggles, Rollers, Flaps, Tilting block.
You do have blowback rifles.
In all firearms, the action needs to keep the chamber shut until the pressure inside is low enough to safely cycle the action.
The pressure generated by a pistol cartridge is low enough that a heavy bolt with a spring can keep the chamber sealed for long enough.
Rifle cartridges have much more energy and generate much higher pressures for much longer. It is not practical to rely only the mass of a bolt as it would need to be very heavy to keep the chamber sealed for long enough.
Instead, the bolt is mechanically delayed through various means. This is also the case on some pistol calibre firearms such as the MP5. It is roller delayed, so the bolt and therefore the weapon, is much lighter than with a simpler bolt.
You do have blowback rifles.
In all firearms, the action needs to keep the chamber shut until the pressure inside is low enough to safely cycle the action.
The pressure generated by a pistol cartridge is low enough that a heavy bolt with a spring can keep the chamber sealed for long enough.
Rifle cartridges have much more energy and generate much higher pressures for much longer. It is not practical to rely only the mass of a bolt as it would need to be very heavy to keep the chamber sealed for long enough.
Instead, the bolt is mechanically delayed through various means. This is also the case on some pistol calibre firearms such as the MP5. It is roller delayed, so the bolt and therefore the weapon, is much lighter than with a simpler bolt.
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