As a long time user of Instructables, I have yet to actually write one up myself. I got bored the other day, and wondered how hard it would be to design a functioning model of an AR-15 magazine. In light of the current political climate, I've been interested in a lot of these topics, and seen several stories online about printing out functioning magazines, but haven't found files that are actually ready to go, and sized properly, so I decided to look around, and see how hard it would be to draw it up myself. It wasn't too bad, but not having a magazine to reference, it took a while to find accurate dimensions. I also don't have a 3d printer, and don't want to spend around $80 to print one up through an online printer, so I haven't been able to prototype this to ensure that it functions 100%, but it should be close.
This method can be used to design a magazine that would hold 1, 2, 5, 10, 15, 20, 30, 40 rounds. It all depends on what you want, and how bulky you want to make it. Then again most models would replicate real things.
Also note that this design does not include a spring. You could wind one out of wire, or print a flexible plastic spring at the same time. I have seen simple springs printed by designing a curved accordion shape, but again, I haven't physically tested something like that.
I designed this in Sketchup, but obviously there are many ways to go about the design process. All of my instructions will use the naming conventions from SU, so if you use something else, I can't be sure that the functions go by the same name, but SU functions seem to named pretty logically.
Step 1: Choose a Magazine to Design
After you have determined what type of magazine you want to design, you'll need to get the necessary dimensions. For an AR-15 magazine, this means the dimensions of the magazine well, as well as the dimensions of the casing, so that you know how to design the individual parts.
Speaking of which, let's look at the parts I've designed...
Step 2: Components of the Design
Here are examples with an inner base (also includes a top cover, not dealt with here), and no inner base.
Step 3: On to the Actual Design Work
Once, you've determined the interior, remove that portion.
Let's look at what makes the interior shape. I have thickened the walls compared to a stamped steel magazine, as this is to be made of less durable material. If you look at a stamped steel magazine, you'll notice the indents, these help hold the rounds inside firmly, so that they aren't moving around causing jams. My thicker walls take care of the smaller indents, but the two bulges on the left go further, since a 5.56x45 round has a thicker case than the actual bullet. These bumps help in feeding. You could chamfer the front end to cut down further on materials, and possibly remove the need for these protrusions, but that's not what I did here, the process would still be similar.
Step 4: Determine the Profile
We'll make a curve, so to start, we're going to draw a simple angle with the "Line" tool, going perpendicular from one corner of the top. Now, I find it easiest to draw along the Red, Green and Blue axises, this ensures you are keeping things straight, granted with the curve, that goes out the window on that portion, but SU is smarter than we think...
After we've determined the basic curve (with the angle), we'll use an "arc" to actually round it out.
I like to start by drawing equidistant lines from the base of the angle.
Then draw the arc, using the endpoints you just drew, and make the curve of it tangent to your lines (since we made them equidistant).
Now, erase the angle, leaving a nice curve for the shape of your magazine.
In the next step, we'll make life easy with a great tool.
Step 5: "Extruding" the Body
When using the "Follow me" tool, remember to follow the line you want to build off, it'll turn red to show what you're following. Once you follow it to the end, you'll have a body for your magazine. Now, we're not done with it, but it does look like a magazine at this point.
Step 6: Magazine Catch
It's easier to measure from a corner so that you place it properly and remember to snap to an axis.
Now that you've drawn it in there, use the "Push/Pull" tool to "push" into the magazine body to the depth you wanted. This goes almost all the way through.
Draw a small vertical rectangle on the botton of the detent, so we can make a stop there. also draw a rectangle toward the bottom for the size of the stop. Remember to right click on the rectangle at the bottom to remove it, we can't have hidden faces like this to print out. You can also erase the line on the vertical rectangle at this point, since it's not necessary, it just keeps the model clean looking.
After that, draw diagonal lines from top of the vertical triangle down to the bottom corners of the lower rectangle. And go ahead and delete the reference line.
Step 7: Feed Lips
You'll need to draw a profile for these that will be strong, but curved on the inside to the radius of the casing of the round. These dimensions are easy to find if you don't have them to hand. Make sure to do it on both sides, or your rounds will fall out.
Now, using the "Push/Pull" tool push them to the distance you need. Now you can add a back for additional strength, or just leave these as is, either way the opening at the back is for the bolt to come through, and pick up a round.
Remember to clean up your lines again too.
Step 8: Follower Stop
It's as simple as closing the top of the follower guide channel, pushing it down, and cleaning up lines.
Step 9: Inner Base
Push that to the thickness you want.
Then, we'll need a protrusion to lock the base plate in place.
Draw the shape you want and push it to the thickness needed. I used the 3d text feature in SU here, but this probably won't work too well, and you'll be better off with a basic shape, say... a circle.
That's it for this part.
Step 10: Base Plate, and Mount
For the runners, determine the thickness you want, they're pretty easy. Draw a line offset from the bottom of the magazine, not too thick, and do it on both sides. After drawing the lines, go ahead and push them to the desired thickness.
There done, except for the actual base.
Copy the bottom of the magazine, this will include the rails, so it's not the same as the original shape made, and make sure to include the shape off your inner base. Clean up those lines.
Push it to the thickness you want, and then we'll make some tabs to grab onto the rails.
On the outer edge, push them a bit and draw a line at the original position to match the rails, then we'll push them up to go beyond the rails.
After they will cover the rails, do the same thing on the inside surface so that they actually grab onto the rails.
Now your base and inner bases are done. We only need to make a follower. Since we custom did the interior, you can't use a commercial follower, unless that is the shape and dimension set you used.
Step 11: Follower
Start with the shape of the inside of the magazine. This will be very similar to making the inner base. First push it to thickness.
After that, draw some lines on the bottom to make anti-rolling tabs that will extend Then erase the faces on the side we're going to cover.
Draw out the length of them from your lines, then connect the dots. You might need to get a little creative on the back side, but that is one area I think you need to play with physically before you get to a good place.
Now go to the top, we need something to push the rounds into their staggered formation.
Depending on the size of the casing, you can make this different, rounds, triangles rectangles, any shape should work, need physical testing, but make sure it protrudes from the top surface. Then we'll push it to length, make sure it doesn't interfere with your recesses for the guides inside the body.
NOTE: if you made a stop for your follower make sure to recess the back channel guide to account for it, other wise it won't come up all the way, and may leave a round loose in the magazine.
Step 12: That Should Do It
Things to remember:
Wall thickness, you don't want this to fall apart, but you want it to work.
You don't have a spring, so this doesn't work without it.
This isn't a tested magazine, and is intended for use as a model, so don't come to me if you break something.
If you liked this please vote for me in the UP! contest. Then I can get some printed up to show what this really looks like.
Lastly remember the law. Some places are crazy strict on stuff like this, so if it's not legal for you to have, you're on your own, I will not bail you out. This was just an academic venture for me, and is in no way intended to be a definitive guide on the legality or safety of using weapons, or their accessories. That being said, it was fun, and I would love have the chance to work on things like this for real, and have a way to prototype.