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Designing A Rifle From Scratch(ish)


Sturgeon
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The rifle now has a magazine (body, at least):

w9axflk.png

 

AxoSjHT.png

 

Turned lines on to highlight some of the details. The magazine is based on a combination of AK, and vz. 58 magazines, and the Gen 3 PMag. Many of the dimensions were taken from the AK-74 magazine which combined with some features from the PMag caused some issues. Protip: Thick feed lip walls are a pain in the ass. However, I was able to work around them without too much difficulty. IIRC, @Ulric you ran into this same issue when designing one of your magazines, thick AK feed lips mean the magazine has to be lower which means the ammo presents lower. Not a huge problem, necessarily, but one worth noting.


Right now, the magazine is supposed to be straight insert, like an AR-15 magazine, but index on a horizontal surface (that big ridge running along the outside of the mag body) like an AK or vz. 58. The rear wall of the magazine is straight and continues a little past the ridge because it will accommodate the magazine catch. 

 

One of my goals was to make the feed tower as short as possible. Currently, it is approximately the same height as an AK. I would like to make it even shorter than that. The reason is that the shorter your feed tower is, the more workable drum magazines become (as they don't need large feed towers, dummy rounds, etc - or at least as many). The limitation on this currently appears to be how thick my polymer lower needs to be for structural integrity. Once I start working on the lower, I may find I can reduce the height of the feed tower even more, which would be nice.

 

Like both an AK-74 mag and a PMag, there are "driving" features in my magazine which point the rounds towards the center of the bore during feeding. This is a particularly good thing in my design as my rounds need to make it in the negative space between two lugs on the barrel extension. But if I can achieve this, then it should give me a very nice, clear feedway. 

 

But, so far so good.

 

 

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Just now, Xoon said:

Out of curiosity, what is your target group for this rifle?
Military, sport, hunting, fun and/or you?

 

It's a project for my portfolio and to improve my SolidWorks skills and also to stave off my sense of personal dread.

 

The rifle itself is designed as if it were intended for the military.

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4 minutes ago, Sturgeon said:

 

It's a project for my portfolio and to improve my SolidWorks skills and also to stave off my sense of personal dread.

 

The rifle itself is designed as if it were intended for the military.

That's nice. 
Are you going for a light rifle, sturdy or is it still up in the air? 
Just to give a example of two rifles that fall in each category:
AG-3, Norwegian produced modified G-3, very rugged rifle which can take a beating and be abused a lot, often joked about being used as a hammer. 
HK-416, new service rifle and very light and ergonomic, though has a few complaints from soldiers transitioning from the AG-3 about it being too flimsy and easy to break.

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42 minutes ago, Xoon said:

Are you going for a light rifle, sturdy or is it still up in the air? 

 

"Yes"

 

I wouldn't put rifles into those sorts of categories, nor neither of those rifles into those categories necessarily. The design processes of making a rifle work reliably making it lightweight aren't exclusive to one another, nor is there a single-dimension metric of either reliability or light weight. A G3 may be a reliable rifle with the right ammo - or it may not be. They tend to have higher parts breakages rates than other guns because their action is fairly violent. They are also, for their caliber, one of the lighter guns of the era (especially when you account for the aluminum magazine). On a similar line, the M16A2 is one of the lightest rifles designed in the 1980s, but good luck breaking one! Likewise, there are guns that are quite heavy and also surprisingly fragile, such as the Stoner 63 or L85A1.

 

Having said all that, I am happy to write a bit about what I'm going for here. Post to follow.

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16 minutes ago, Sturgeon said:

 

"Yes"

 

I wouldn't put rifles into those sorts of categories, nor neither of those rifles into those categories necessarily. The design processes of making a rifle work reliably making it lightweight aren't exclusive to one another, nor is there a single-dimension metric of either reliability or light weight. A G3 may be a reliable rifle with the right ammo - or it may not be. They tend to have higher parts breakages rates than other guns because their action is fairly violent. They are also, for their caliber, one of the lighter guns of the era (especially when you account for the aluminum magazine). On a similar line, the M16A2 is one of the lightest rifles designed in the 1980s, but good luck breaking one! Likewise, there are guns that are quite heavy and also surprisingly fragile, such as the Stoner 63 or L85A1.

 

Having said all that, I am happy to write a bit about what I'm going for here. Post to follow.

You have a point, but I think I was a bit unclear. I meant making the rifle more abuse proof that normal, not sincerely more reliable. 
For example stronger charging handle, as the HK416s is easy to break with too much force, thicker frame which does not bend or get dented that easily. Soldiers do the weirdest things with their rifle, including using them as chairs, hammers and spears. 

I appreciate you taking the time to answer my questions by the way.

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Just now, Xoon said:

You have a point, but I think I was a bit unclear. I meant making the rifle more abuse proof that normal, not sincerely more reliable. 
For example stronger charging handle, as the HK416s is easy to break with too much force, thicker frame which does not bend or get dented that easily. Soldiers do the weirdest things with their rifle, including using them as chairs, hammers and spears. 

I appreciate you taking the time to answer my questions by the way.

 

I was sort of lumping reliability and durability together. The AR-15 charging handle has always been a bit of a kludge, but charging handles are a very difficult human engineering problem so it's stuck around (it has many advantages). It's not terribly surprising to me that an army transitioning from the G3, which takes a herculean amount of effort to charge, to an AR derivative would see some charging handle breakages. At the same time, the USMC (perhaps most notorious for being filled with people who can break and/or lose ball bearings given enough free time) has not really had a serious issue with charging handle breakages in the M16/M4 platform in the last 50 years. So I assume that's more an issue of adjustment than anything else. Those charging handles do break, though. One of the easiest field remedies for this is to just carry spares. They are cheap and light and easy to replace in the field, so it's not a huge issue.

 

No weapon can be truly "soldier proof". AKs are not, G3s are not, FALs are not, M1 Garands are not. Even Mausers can and do break. Of course it's important not to equivocate: Some rifles are not properly engineered for durability and are not appropriate for use by soldiers at all. I would definitely say the AR-18 is an example of such a rifle. They are extremely fragile in a number of important ways, and it's obvious why they didn't catch on militarily (though the AR-18 bolt group was copied by a number of lazy designers). The early M16 was also too fragile. There could be a very interesting discussion of what "underbuilt" really means with regards to rifles that would almost exclusively cover AR-15 variants. They run the gamut. The first 17 AR-15s were so light and fragile that a whole host of changes were proposed during testing in the 1950s which caused them to gain three quarters of a pound by the time they hit production as the Colt 601. Being underbuilt by that much is perhaps one of the most extreme and clear examples I can find. The 601, though, was still too light and by the time development of the M16A1 was done it would weigh 0.69lbs more than that, almost a pound and a half heavier than the first 17 prototypes when they came out of Armalite's shop. Not all of that weight was to improve durability or reliability, but almost all of it was. And even then, the 1970s era M16A1 still had shortcomings in durability, which led to the M16A2 growing by another half-pound. So the total difference between the M16A2 (which was fully ruggedized) and the first 17 AR-15s was nearly two pounds - that's more than even the weight growth of the Dutch AR-10, which grew by about 1 2/3s pounds over its development! The AR-15 is a smaller caliber rifle, too to so when we compare these in terms of percents the degree to which the initial AR-15 was underbuilt becomes very clear:

Dutch AR-10: Grew by 1.66 lbs (23% of initial weight)

 

AR-15: Grew by 1.92 lbs (34% of initial weight) (!!!)

 

So while a weapon cannot be soldier proof, nor is weight necessarily an indicator of ruggedness, it's also clear that it's very bad to under-engineer a weapon to such a degree as the original AR-15. If you do, then the next decades will be spent fixing your shit.

 

 

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1 minute ago, Toimisto said:

BTW, in which way is the AR-18 too fragile? and how would those be corrected.

 

Handguard, front hinge point, stock, fire control elements. The way to correct them would be to beef up all of those elements, but tbh it would be better to just redesign the rifle from scratch. Which is what most did.

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There were a few things I wanted to do with this rifle. First and foremost, I wanted a roughly "AR-like" rifle that incorporated all or most of the reliability elements I had identified in the AK series: Friction reducing anti-rotation devices, long bolt overtravel, a large degree of underslide, and a clear ammunition feedway, to name some of them. At the same time, I wanted my execution of those features to be different than the AK, as "stuff an AK up the ass of an AR" has been done about thirty fucking times by this point. I also deliberately eschewed some of the design characteristics of the AR-15, such as the tube-shaped receiver and cylindrical bolt carrier, because I did not want the end product to be basically just a "redux" of the AR, either.

 

Another feature I wanted to include was an extruded upper receiver because I had some ideas about how to do it while making it lighter, cheaper, and more adaptable. Also, three years ago I designed an optimized bolt lug contour, which I modified slightly and used as the basis for my bolt configuration. This contour was designed to maximize lug contact area, minimize lug rotation angle, and clear the rifle's feedway. You can see images of the study I did in 2015 below:

 

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The lug configuration I ended up using was the one in the second row of the last image, far right.

 

I knew at the beginning that I wanted the rifle to be in 5.56mm by default. I also wanted it to be expandable to other calibers, so the diameters and lengths of the bolt, barrel extension, and other elements are hybridized between the AR-15, AR-10, and SCAR. It should be able to take conversion kits for rounds as big as .308 without any issues.

 

I deliberately chose not to use USGI magazines for the rifle, for several reasons. Chiefly, the magazine is one of the most significant elements of the rifle and I wanted to design it myself. Second, AR mags are crap and designing your rifle around them is like designing a Formula-1 car to run on 87 octane. Third, the AR magazine well interior (which is necessary to make AR mags work) would not have allowed me to design a highly reliable and efficient drum magazine, which is something I am interested in.

 

For the gas system, I chose to use a gas-tube-to-tappet arrangement because of the chosen bolt carrier configuration and to prevent gas from being blown into the receiver. Not that this is a major limitation of the AR series, but... Why not?

Beyond all that, I designed everything to be both lightweight and durable, which means being very conscious of volume economy. Bigger guns are heavier and more fragile. Smaller guns are lighter and more robust. Because that's how mass works. So being small (within the parameters I set for myself) was important to me.

 

 

 

 

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4 hours ago, Sturgeon said:

 

I was sort of lumping reliability and durability together. The AR-15 charging handle has always been a bit of a kludge, but charging handles are a very difficult human engineering problem so it's stuck around (it has many advantages). It's not terribly surprising to me that an army transitioning from the G3, which takes a herculean amount of effort to charge, to an AR derivative would see some charging handle breakages. At the same time, the USMC (perhaps most notorious for being filled with people who can break and/or lose ball bearings given enough free time) has not really had a serious issue with charging handle breakages in the M16/M4 platform in the last 50 years. So I assume that's more an issue of adjustment than anything else. Those charging handles do break, though. One of the easiest field remedies for this is to just carry spares. They are cheap and light and easy to replace in the field, so it's not a huge issue.

 

No weapon can be truly "soldier proof". AKs are not, G3s are not, FALs are not, M1 Garands are not. Even Mausers can and do break. Of course it's important not to equivocate: Some rifles are not properly engineered for durability and are not appropriate for use by soldiers at all. I would definitely say the AR-18 is an example of such a rifle. They are extremely fragile in a number of important ways, and it's obvious why they didn't catch on militarily (though the AR-18 bolt group was copied by a number of lazy designers). The early M16 was also too fragile. There could be a very interesting discussion of what "underbuilt" really means with regards to rifles that would almost exclusively cover AR-15 variants. They run the gamut. The first 17 AR-15s were so light and fragile that a whole host of changes were proposed during testing in the 1950s which caused them to gain three quarters of a pound by the time they hit production as the Colt 601. Being underbuilt by that much is perhaps one of the most extreme and clear examples I can find. The 601, though, was still too light and by the time development of the M16A1 was done it would weigh 0.69lbs more than that, almost a pound and a half heavier than the first 17 prototypes when they came out of Armalite's shop. Not all of that weight was to improve durability or reliability, but almost all of it was. And even then, the 1970s era M16A1 still had shortcomings in durability, which led to the M16A2 growing by another half-pound. So the total difference between the M16A2 (which was fully ruggedized) and the first 17 AR-15s was nearly two pounds - that's more than even the weight growth of the Dutch AR-10, which grew by about 1 2/3s pounds over its development! The AR-15 is a smaller caliber rifle, too to so when we compare these in terms of percents the degree to which the initial AR-15 was underbuilt becomes very clear:

Dutch AR-10: Grew by 1.66 lbs (23% of initial weight)

 

AR-15: Grew by 1.92 lbs (34% of initial weight) (!!!)

 

So while a weapon cannot be soldier proof, nor is weight necessarily an indicator of ruggedness, it's also clear that it's very bad to under-engineer a weapon to such a degree as the original AR-15. If you do, then the next decades will be spent fixing your shit.

I see, you have taken a lot into consideration. 

One thing I think you should keep in mind later, is to make the rifle winter/arctic friendly, bigger trigger guard or the ability to flip it away or remove it. 
Any cast part can be skeletonized for weight savings i think too. No styling, basically, not this:

latest?cb=20100307170239

 

Oh and, If you want some advice on making parts more automation/mass production friendly, just ask. 

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5 hours ago, Sturgeon said:

 

Handguard, front hinge point, stock, fire control elements. The way to correct them would be to beef up all of those elements, but tbh it would be better to just redesign the rifle from scratch. Which is what most did.

Auto sear/Sear trip, especially so.

Saw more than a few with the "H" piece at the rear of the receiver , knocked loose.

 

And "E clips, Everywhere".

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1 hour ago, Xoon said:

I see, you have taken a lot into consideration. 

One thing I think you should keep in mind later, is to make the rifle winter/arctic friendly, bigger trigger guard or the ability to flip it away or remove it. 
Any cast part can be skeletonized for weight savings i think too. No styling, basically, not this:

latest?cb=20100307170239

 

Oh and, If you want some advice on making parts more automation/mass production friendly, just ask. 

 

Concur, I am not a fan of stylization on a rifle. Aesthetics should be incorporated where they don't interfere with anything else perhaps, but the "Audi treatment" is haram.

 

The AK is a good example of the correct application of aesthetics in a rifle, actually.

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6 hours ago, Toimisto said:

BTW, in which way is the AR-18 too fragile? and how would those be corrected.

 

On the AR-180B reproductions made by Armalite, the lower receiver hinge point is quite weak.  On the originals it's fairly beefy though.  Biggest complaint on the originals is the folding stock mechanism; that thing is just a pile of crap.

 

In general though, the AR-18 was cheap and not very good.  There were several good ideas that a lot of people lifted, like the broad design of the bolt carrier, but you'll note that very few countries elected to make complete clones.

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2 hours ago, Sturgeon said:

 

I've actually never seen one in person, let alone 3 actual -18s in the same collection.

 

 

That's what I figured.

 

The hinge hole consists not only of the end plate that's welded on to the front of the magwell, but also of an extension of the receiver itself.  The hinge hole is twice as thick as any other point on the rifle's receiver.  If the hinge point is a specific weakpoint, then you might as well throw up your hands and say that the entire damn rifle is flimsy.

 

But I would expect the stock hinge, last round hold open, handguard, or the really dodgy welds at the back of the upper receiver to go first.

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3 hours ago, Collimatrix said:

 

 

That's what I figured.

 

The hinge hole consists not only of the end plate that's welded on to the front of the magwell, but also of an extension of the receiver itself.  The hinge hole is twice as thick as any other point on the rifle's receiver.  If the hinge point is a specific weakpoint, then you might as well throw up your hands and say that the entire damn rifle is flimsy.

 

But I would expect the stock hinge, last round hold open, handguard, or the really dodgy welds at the back of the upper receiver to go first.

Quality issues with the welds? 

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