I'll just briefly go over the process I used. To make the molds I used "Instant Mold". Look it up on the Internet, it's great stuff. There are lots of different ways to cast things. I'm using a very simple method of press molding and will be making a 2 part mold. Do some searches for press molding if you're interested in trying it for yourself.
The first thing you'll want is something to contain your molding medium (instant mold) while you press whatever you are casting into it.You can use anything really. I used part of a container that my magnets come in.
I sat the piece of tubing on a flat surface (my work table) and pressed a bit of instant mold in the tubing trying to make it as flat as possible. Then I took my piece and pressed it halfway or so into the instant mold. Next we let it cool. I throw it in the freezer for a few minutes.
After that I took a bit more instant mold and pushed it into the tube, covering the other half of the backpack and leaving a little bit of room at the top.
I then placed the black end piece in the tub and pushed down on it very firmly with my palm. This is to ensure that the instant mold gets into all the little crevices of the backpack.
Threw it in the freezer for a few minutes to harden. Before separating the two sides of the mold, I made a line across the two halves so I can be sure to properly align the mold when I cast my piece.
Finally I separate the two halves and pull out my original piece. I then go through the same process for the boltgun bit.
Now I didn't get any pictures of the actual casting process but it's very simple and much like creating the mold. I used Milliput fine cast as my casting medium. I put one half of the mold back into the tube. After mixing up the putty I started with small pieces and pushed it into the deepest crevices of the mold first and worked my way up to a little over flush with the top of each half of the mold. Then, I put the other half of the mold into the tube and line them up using the mark I made earlier. I used the black end piece once again and pressed hard with my palm. I let it sit for about 24 hours and then carefully removed the milliput from the mold. When I pulled them out they had flash ( extra casting material around edges) all around the edges where the excess putty goes when the two halves are pressed firmly together. This is normal and you want some flash. You have to put in enough putty otherwise the putty will not fill the mold entirely and you will get a bad cast. Here are shots of the two pieces after cleaning off the extra flash around the edges. I made two of each piece. They are not perfect but should do just fine.
And here they are painted up and glued on.
And some comparison shots
These shots are of the actual originals that were used and the casted pieces.
These were my first attempts at casting with a 2 part mold. For a first effort, I'm very happy with how they came out.