I guess I'm overdue for an update.
The first half of the mold was filled. Then I screwed a top onto the box, flipped the whole thing over, and removed the bottom of the box:
Then the parting wall was removed:
After spraying a lot of release agent to keep the silicone from bonding to the cured first half of the mold, it was time to start pouring the second half:
The last thing to do on the main body was to pour a silicone plug so that the castings will have a cutout to fit the separately cast barrel piece:
Once that was cured, the next thing to do was to disassemble the mold box. Here it is with the top and bottom removed:
And with the sides removed:
Then I just had to pull the two mold halves apart:
And remove the prototype:
Once the prototype is out of the mold, it's time to rebuild the mold box. I started by taking the wall parts and shaving about a quarter of an inch off of them with the table saw. Once that was done, I screwed them back onto the bottom piece of the mold. Then I fitted the top edge with hanger bolts so I could use wing nuts to hold down the top of the box.
With that done, it was time to pour the first casting. Since the finished casting is going to be huge, I decided to reduce the weight a bit by adding in a couple of foam blocks. To keep them in place, I started by pouring a small batch of resin into one half of the mold and setting the foam blocks on top of it while it was still not quite cured:
Then I set the other half of the mold into place, screwed down the lid, and stood the whole thing up on end:
Filling the mold took just under a gallon of resin, even with the foam blocks in place:
Once the resin had cured, it was time to open up the mold again:
And then goof around for a minute:
So that's the first casting of the main body. I've still got molds to make for the small parts. Here's the finished prototype for the barrel:
Here it is under the rubber for the first half of the mold:
And the finished prototype for the drum magazine:
I should be molding that piece today. Stay tuned...