AR-15 sheet metal and tube upper receiver

[justin22885]

no gap on my AR-18 mated to the AR-15 lower, but i sized the bolt carrier to fit the AR-15 trigger group, its not exact and even though i have the collapsible stock on there for show if i were to build that id probably put a side folding hinge on it

and to answer MachIVshooter, it uses the dual guide rod with springs on an AR-18 style carrier, and the front of the guide rods retain the upper handguard so ones the rifles field stripped the upper handguard comes off for cleaning the gas system, AR-15 handguards work because i created an adapter that allows the AR-15 handguards to be installed like AR-18 handguard

 

[justin22885]

i have a lot of designs, AR-18 upper you see above, the scar like rifle, my favorite on the bottom of page 1, i have a delayed blowback tube gun using G3 parts, an AR18/AK hybrid where one guide rod is used as a long-stroke piston, a simplified FG42 rifle, i just keep trying to get simpler, and simpler without necessarily taking away from the features

there are so many variables and tradeoffs to decide what is perfect, like gas system, long stroke, short strike, DI?.. caliber? focus on .308, 5.56, or 7.62x39?, which magazines to design around?, try to use pre-existing forearms, or just go monolithic by extending the top half of the receiver? each of these have their tradeoffs, not easy to determine which set of tradeoffs is the best

 

[justin22885]

well, for anyone who's interested, the sheet metal and tube AR-15 upper i feel is finished, so i uploaded the CAD files here

https://grabcad.com/library/ar-15-sheet-metal-and-tube-steel-upper-receiver-1

 

[d2wing]

If you are looking at home built, I think Aluminum is better for most. I think it would be easier to smelt scrap and make a mold from existing parts, and cast anew part. It would require finish work with hand tools but I think is more doable than using steel pipe in an AR design. Might work in a simpler design.

 

[justin22885]

youre going to have an easier time finding decent enough sheet metal than you would finding and smelting aluminum, some guy pounded a shovel flat and folded it into an AK receiver, you could take sheet metal off the side of a truck.. anything you try to smelt from scrap aluminum will likely turn out poorly, plus you cant really weld on it either and any alloy youre going to come across will generally get worn very quickly by steel, cast aluminum made from random unknown alloys will likely yield a very weak result

anyway, for anyone wanting to view the files i posted a link to and get the measurements from i recommend using the free edrawings viewer.. and browse around grabcad and you'll find complete 3D models for all sorts of firearms, i even found the models to the STG44 and FG42 on there recently

 

[lysanderxiii]

Aluminum is very easy to cast.

You can melt aluminum cans in a good hot campfire and pour it into a mold.

I have seen aluminum Army cots melted into puddles after a tent fire.

 

[lysanderxiii]

no gap on my AR-18 mated to the AR-15 lower, but i sized the bolt carrier to fit the AR-15 trigger group, its not exact and even though i have the collapsible stock on there for show if i were to build that id probably put a side folding hinge on it

and to answer MachIVshooter, it uses the dual guide rod with springs on an AR-18 style carrier, and the front of the guide rods retain the upper handguard so ones the rifles field stripped the upper handguard comes off for cleaning the gas system, AR-15 handguards work because i created an adapter that allows the AR-15 handguards to be installed like AR-18 handguard

Making a new bolt carrier?

Now, you are introducing some real heat treating issues for the garage mechanic....

In any case, have fun, and be sure to post pictures when you get your prototype finished...

 

[MachIVshooter]

youre going to have an easier time finding decent enough sheet metal than you would finding and smelting aluminum, some guy pounded a shovel flat and folded it into an AK receiver, you could take sheet metal off the side of a truck

While there's a certain romance about the vision of being able to make guns or other tools in a post-apocalyptic Road Warrior type world, the reality of it is that there's not going to be any shortage of small arms even if it does all fall apart, especially not here in the USA where there are enough to arm 9 out of 10 citizens.

If your concern is really being able to continue shooting when Armageddon comes, I'd focus more on ammunition than small arms. What good is your shovel AK or plumbing pipe AR if there's no powder, primers or bullets to be found?

.. anything you try to smelt from scrap aluminum will likely turn out poorly, plus you cant really weld on it either

Cast aluminum welds just fine, so long as it's clean. On that note, corroded or contaminated steel doesn't weld for poo, either.

and any alloy youre going to come across will generally get worn very quickly by steel, cast aluminum made from random unknown alloys will likely yield a very weak result

That's why it would be important to understand alloys. Even if you're only using steel, you still need to. Yeah, you can make some of the parts out of low carbon hot or colled rolled, A36 cast, 1018, etc. But barrels and bolts? Not if you care about your life. You need to know what properties make certain alloys appropriate and others a very bad choice. You also need to know how to properly heat treat and temper them, unless you wish to have a hand grenade that looks like a rifle.

 

[justin22885]

you have a point about ammunition, it is most certainly the weak link in all of it, and of it the cartridge case itself is the weak link, ive considered things like extended harmonica magazines, trounds which can be 3D printed or easily made from plastics, bimetal cases that use a steel case head crimped to an aluminum or brass body, and straight up caseless,

of these the two pieces cases is probably the easiest to do, trounds while cool require an entirely new weapons system to work, though imagine a rapid firing rifle ballistically equivalent to a .308, but could work on the action of a DA revolver requiring no gas system, and a harmonic rifle designed to use a longer mag is probably the most low-tech rapid fire solution with a significant capacity, though harmonicas will be heavy

 

[Nuclear]

Primers are the hardest item of modern firearms to produce should everything go south. Barrels are difficult too, but they don't wear out very fast.

 

[MachIVshooter]

Primers are the hardest item of modern firearms to produce should everything go south

Not really. There are a number of ways to reload primers, some safer than others. Perchlorate is one that I've personally used with success.

Bullets can be cast, extruded, swaged or machined. Same for cases.

Powder is more difficult. No, it's not that hard to make nitrocellulose. But to make a solid, stable, powerful variety that won't blow up your gun is another matter entirely.

 

[justin22885]

powder isnt even all that hard and can be done safely with relatively basic equipment, nitrocellulose as stated is easy to make and if youre making an expedient smokeless powder youd probably want to stick with a single-base powder anyway, i have some recipes for some of the simpler single based cordite products that can be economically done on a small scale, easier than the machinery needed to extrude brass

 

[d2wing]

Aluminum for a complex AR upper make way more sense. If you can build one out of steel do and post step by step pictures like a real gun builder would do. Otherwise you are just blowing smoke on an untested and impartial idea.

 

[JDGray]

Justin really, really hates aluminum! It can be found in a thread I started on a CZ97, and I think there's another CZ discussion on them too. Aluminum is junk for guns, in his mind.