Well my friend, since you did ask so nicely I'll attempt to give you something of a tutorial on how I did this, although I must warn you most of what I did was free handed while looking at reference pictures so expect to be doing a lot of that yourself.
Schankerz' Super Rad Halo Reach DMR Tutorial
So the file I used was the sliced DMR file, if you look up "DMR" in the file archive (it's still there on the old site I checked) it's the "Halo Reach M329 DMR (Sliced)" It's pretty hard to miss it.
Now when you take a gander at the file it looks like this:
But you only need a few of the pieces from this file, I've circled the ones you need in red, the rest you can just move off to the side.
Now once you have these pieces organize them so they look like this, the reason being so you can scale the gun to your liking.
Now if your thinking why I onlt have one section of the gun shown here is becasue you're going to use those two front pieces (mid and forward sections) three times, the hollow back section once, and the full back section twice. This gives the gun it's thickness and leaves that hollow space in the middle for your removable mag. shown here:
(side note: That rectangular hole in the front section where the barrel goes is only for the middle section, for the two outer sections just keep drawing straight over that part so it looks like it does in this picture)
Once they're printed just tape it back together to form the full template so you can trace it onto your foam, but do tape the handle guard piece to the full template, that gets added on separately since its a smaller thickness than the gun. It's instead a thickness of two, not three:
Also before you trace the template onto the foam *IMPORTANT* make sure to cut off this top section of the gun shown by the red line here:
It's not accurate to what that section looks like in-game and honestly makes it a lot easier to just add that section later as a separate piece. (you will not be using that cut off template later so you can just toss that away) You can see what that top section looks like in this picture, note that's just the basic shape of it without any details yet, and when you do make that part the thickness I had for it was two, you can change it if you want but that's how i did it.
Now if I've told you how to do this correctly you can start adding a more 3D look to the gun, starting with looking at the above shown picture with the long rectangle piece that covers the length of the gun. It just takes some measuring at refrence pictures to figure out that piece so I won't stay on it too long, just make sure you leave room to put on that butt section at the very end of the gun, again just look at your pictures and trace out where everything goes on the basic template before you start going all willy-nilly with the add on sections.
Now for the bottom front section of the gun, the part where you place your other hand, to make it pop out more you're going to cut that whole bottom part out along these lines:
You're then going to add a fourth layer to your cut out section, then glue it back in place. Now if perhaps you want to make this easier or don't have a good craft blade you can cut that section out of the paper template beforehand then add the section in later but this is how I did it so to each his own.
Now assuming you're still following me heres a few more things to know:
This is the magazine, it's really simple and assuming you do it right it should come in and out of its slot with relative ease once you've done it a few times.
Also I didn't realize this when I first started but the section of the template where the trigger is is a bit off from what it looks like in game. It was a relatively easy fix but if you want to avoid making these changes yourself just update your template accordingly so it looks more like this:
Now for the rest of this I'm going to leave pictures of what I have so far so you guys can figure out the rest, by following these pictures and your own reference pictures it's relatively easy to figure out. Word of advice though, keep those paper templates with you for the whole build, they come in handy when your trying to figure out where details should go.
Again I will tell you mostly everything here was free handed using reference pictures, when doing this yourself I highly recommend getting A LOT of reference pics, they're pivotal in the making of this gun.
Items used so far: EVA foam, craft foam, contact cement, markers, craft knife, dremel, heat gun.
Now of course since this not yet a finished product I can update this tutorial once new progress is made and if there's anything else you want me to add or want to know I will add it in as well.
Thanks for reading everybody and I hope some of you find this useful!
Take care all.