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Would having the gas piston or impingement system below the barrel instead of on top help in reducing recoil?


pizza654
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This is my first post and im no physicist so if this sounds stupid to you please explain to me why its dumb because I always like learning new things about gun design. Anyways ive had this idea in my head for a while now about a rifle concept and it first popped into my head when I was looking at the mechanics of a pkm. Like a lot of belt fed guns the piston is on the bottom of the barrel instead of the top and because the bolt and piston is so low it gives the pkm a good recoil impulse. My thought was how come no ones ever designed a rifle with the gas system below the barrel instead of on top? Imagine a SCAR but the barrel and the piston gas block is reversed.

 

 

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14 hours ago, pizza654 said:

This is my first post and im no physicist so if this sounds stupid to you please explain to me why its dumb because I always like learning new things about gun design. Anyways ive had this idea in my head for a while now about a rifle concept and it first popped into my head when I was looking at the mechanics of a pkm. Like a lot of belt fed guns the piston is on the bottom of the barrel instead of the top and because the bolt and piston is so low it gives the pkm a good recoil impulse. My thought was how come no ones ever designed a rifle with the gas system below the barrel instead of on top? Imagine a SCAR but the barrel and the piston gas block is reversed.

 

 

 

Moving the barrel higher typically makes recoil management much more difficult. Plus, if the gas system is below the barrel, you have to route around the magazine somehow. That introduces manufacturing complexity and structural weakness in a part that sees significant forces (the operating rod).

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Does the AUG or F2000 pull sideways because of the location of their gas pistons? No. Whatever thrust you have on the gun will be too close to axis of the barrel to matter recoil wise... climb more specifically. Location of the thrust imparted to the operating system does matter, but in terms of keeping the carrier (or whatever similar component you have) from tilting and causing stress and wear, ideally you want the trust be as in line as possible with the bolt or bearing surfaces.

 

The reason why most machine guns have their gas system on the underside is to free up space for the belt feeding mechanism, there are exceptions however.

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  • 4 weeks later...

There are a bunch of semi automatic hunting rifles that have solved this problem. The reason for placing the gas system below the barrel is that it fits nicely into the handguard. This makes the rifle keep a traditional and slim profile. In general, they are much lighter than for example the M1 Garand, but they have a lot of small parts and are kind of messy to disassemble. This is afforded by the designers because they have access to modern manufacturing methods, and their customers rarely have to take the rifle apart in a hurry, or in the dark, or in the rain. One positive side effect of this layout is that it moves the recoiling mass down. All of these rifles are sold primarily with traditional stocks, but having the recoiling mass below the barrel somewhat compensates for the lack of an in-line stock.

I've spent a lot of time thinking of how I'd design my dream hunting rifle. I've ended up deciding that it's worth it after all to put the gas system below the barrel. It really creates a whole host of problems. I despise the cuckoo clock engineering on rifles like the modern Browning Bar (not the lmg), but it's hard to move the impingement force from the gas port to the bolt carrier in a satisfactory way. You also don't want a heavy and bulky op rod like the Garand design. And I want the bolt carrier to be easier to get out of the rifle than in the Browning Bar or H&K SLB 2000 (or worse yet - the Remington semi autos).

The nicest design in this category is definitely the Benelli R1. It has a wonky gas piston system it and hides the recoil spring in the stock, like a lot of semi automatic shotguns. It is the only rifle of this kind that has an acceptable takedown procedure. It's not perfect, but for a rifle that can be chambered in .338 Win Mag it is very nimble and nice to handle.

As a comparison, google the youtube video with a guy that takes the bolt carrier out of his FNAR. "FNAR disassembly". Compare that to how you get the bolt out of an AR-15, or an AK, or any other rifle designed without a strong traditionalist aesthetic requirement.

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On 11/19/2020 at 3:32 AM, Miroslav said:

There are a bunch of semi automatic hunting rifles that have solved this problem. The reason for placing the gas system below the barrel is that it fits nicely into the handguard. This makes the rifle keep a traditional and slim profile. In general, they are much lighter than for example the M1 Garand, but they have a lot of small parts and are kind of messy to disassemble. This is afforded by the designers because they have access to modern manufacturing methods, and their customers rarely have to take the rifle apart in a hurry, or in the dark, or in the rain. One positive side effect of this layout is that it moves the recoiling mass down. All of these rifles are sold primarily with traditional stocks, but having the recoiling mass below the barrel somewhat compensates for the lack of an in-line stock.

I've spent a lot of time thinking of how I'd design my dream hunting rifle. I've ended up deciding that it's worth it after all to put the gas system below the barrel. It really creates a whole host of problems. I despise the cuckoo clock engineering on rifles like the modern Browning Bar (not the lmg), but it's hard to move the impingement force from the gas port to the bolt carrier in a satisfactory way. You also don't want a heavy and bulky op rod like the Garand design. And I want the bolt carrier to be easier to get out of the rifle than in the Browning Bar or H&K SLB 2000 (or worse yet - the Remington semi autos).

The nicest design in this category is definitely the Benelli R1. It has a wonky gas piston system it and hides the recoil spring in the stock, like a lot of semi automatic shotguns. It is the only rifle of this kind that has an acceptable takedown procedure. It's not perfect, but for a rifle that can be chambered in .338 Win Mag it is very nimble and nice to handle.

As a comparison, google the youtube video with a guy that takes the bolt carrier out of his FNAR. "FNAR disassembly". Compare that to how you get the bolt out of an AR-15, or an AK, or any other rifle designed without a strong traditionalist aesthetic requirement.


I don't know that I agree about the Benelli R1, but my experience is with the MR1 and it might be somewhat mechanically different. It was a nightmare to disassemble and reassemble it.

But you're right about the rest of "sporting rifles", they all suck tremendously.

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