Return of the Jedi Proton Grenade / Bunker Buster prop


New Member
Greetings! While researching my Proton Grenade prop (often also called a Bunker Buster) from Return of the Jedi, I kept finding great threads on here, as I always do over the years. Because I am taking photos during the build, and am trying something different in a few places than other builds, I thought I should document it here. The finished prop will be magnetic, and have lights, that are activated by turning the top handle, with a ratchet noise.

The primary kit is one from Van Oaks props (who has posted his things here), which is a 3D printed body and base, and then some really smooth resin-printed detail greeblies. Here is what is in the kit, along with a replacement clip piece I added (kit piece was lost):

And here is what I am building, pics of the original props:


I am replacing a few other pieces, notably two original (but mirrored orientation) vent greeblies I ordered from Wanna Wanga, and the small LED light covers. I am also using my own inner axle for the top knob, which will be part of the internal switch mechanism. Because I wanted to be able to change the battery, I am adding a bolt closure from the bottom. The small magnets it was built for didn't seem that strong, so I modded it to allow for two larger magnets. At the moment of this posting, I have only the electronics to complete, so we will see how that goes.

To start with, I mentioned I lost the resin printed little cable clip greeblie. I decided to just create one from scrap. My first attempt was in ABS plastic, but heating it warped and shrunk the clip, so I went with the next, more obvious choice: Galvanized sheet metal. I took a mending plate, drilled two holes, filed them to meet into a lozenge shape, cut it out with a jig saw, and bent it. Aside from the missing lettering, it has the right look:

Prepping the print: For the main 3D print, I used XTC-3D, a sort of two part mixture that is self-leveling. It works really well in flat places, a little trickier on curves. The trick I have learned with this stuff is to mix very small batches. You have about four or five minutes of really nice self-leveling time, before it begins to thicken. It is tempting to keep going, but I have learned that at this point, it just means more sanding in your future. It takes about 2 hours to dry enough to handle, so this is something I do over several days, mixing about three or four batches over a day. For the main cylinder, I placed it on two chopsticks and only applied to the top. for the flared cuff, I kept the application area level, by propping it up to dry against an object, turning that 45 degree angle into a 0 degree angle. It also will fill in details, so if your prop has grooves or anything like that, this product will not be ideal (the primary issue on this prop are the holes on the lower cuff). On the top details, it sort of filled in the lower corners, so that had to be cleaned up. On the main body, done in about four applications (turning each time), it had a line of drips that needed sanding.


Cleanup: Primarily done with 350 grit sandpaper, it is really easy to sand once cured, and not a huge issue. Sanding the ribbed underside of the flanged piece, and the top depressions were the hardest part. I used a drill bit by hand to sort of re-drill out the 4 or 5 holes that filled in. I used a Dremel stone wheel on the lowest setting to clean up the underside of the flange, and the top depressions:

Magnets: The kit comes with nice slots for some common small rare-earth magnets (two in each hole, and a cover to seal in all 8). I tested the strength of that setup, and knowing I would have a 9v battery in there, I opted to make bigger spots for two larger, stronger magnets. I used a large flat drill bit, and some woodcarving gouges to free it all up, before gluing the magnets in and the cover on (I used a file to score a scratch detail that crossed the cover and lip, so I could line it up when gluing by matching the marks). This may have not been ideal (see next step for why). Also shown here, I planned on opening the prop to change batteries (and probably troubleshoot my switch), so while it did press-fit tightly together, I wanted a strong backup. Not having a tap and die set I opted to take a lamp mount that had those threaded bolt holes, and cut it into a bracket, which I will glue in. It will line up with the center hole, and a bolt will thread into it once it is closed:

Filler Primer: As the next step of prep on the print, I used filler primer. After priming, the pieces are almost "fuzzy" with primer, and I use steel wool all over, and then burnish the parts with a paper towel, to get a polished surface, ready for paint. The downside to this was, the steel wool sheds small iron filings, and those super magnets grabbed them all. I had to use other magnets to pull it clean for painting.

Painting: I had planned to get that nice texture of the original props by using this fine "stone" texture paint, and sanding it off. Turns out, the can I bought was a return, and the ball didn't rattle, the spray nozzle was missing, and the stem was pushed into the can. So I had to try a backup plan I have seen some use for texture: Spray Adhesive.

So I lightly dusted it with adhesive spray, waited a few hours for it to get LESS tacky, and then coated with my Nutmeg Rustoleum. After it dried, I noticed the texture was sort of bubbly, and took a bone burnisher to rock over them and flatten down those bubbles, and then let it cure overnight.

For the silver pieces, I used a base of the Rustoleum Metallic, using a great trick by VanOaksProps of using double-stick carpet tape to keep those super tiny bits stuck while spraying them. The little knurled bolts would have for sure rolled around. Once the silver pieces dried, the next day I used Rub 'N Buff to burnish in a slightly better metallic look.

Once the main body had dried, the texture was too bumpy overall, which I had anticipated. To get the prop's original look, it needed texture that gets sanded down, leaving more plateaus with valleys, rather than mountains. So I sanded it down, especially on the edges, and then re-painted it one last time to get the finished look:

For the stripes, I kept going back and forth weather or not to include the smooth "tape" rectangle on the yellow stripe. In the end, it just seemed right, so I cut a rectangle of yellow adhesive vinyl from my vinyl cutter stock, and adhered that. Then I used fine sand paper to take off the shine, and then mixed some acrylic to make the colors. I used the ones on the left to mix the yellow (a touch of red in it, as it appears a little orange), and then the ones on the right to make the red (but I kept some of my yellow wet, and added some into the red to bring it a tiny bit toward orange as well). I used tape (purple "delicate" tape) to get some edges, but not all, so I could keep some of that brushed look, especially on the lower edge of the red stripes along the flange. There is a red spot under the vent greeblies on the top behind the rectangular slot, so I marked those spots and painted them. It took a few coats of each to get opaque, so in between I put a wet paper towel over my paints and they lasted a few days. After painting these stripes, I did a pass of satin clear coat to help seal it all down for the next vinyl decal part.


Lettering: These props were made well before Aurebesh had ever been codified, and there are several different lettering types. I one one Prop Store prop it has lettering on only one side, but I am not sure about the others. So I created the two you see in the movie, the letters for one side, and the blocky symbol on the other:

I made the in vector using Adobe Illustrator, and cut them out as masks using some "removable" vinyl sheet. They are fairly small, the words are just over an inch long overall. The slight wonky nature of the letters, which I re-created, points to these being done by hand, probably on white tape that was adhered, and then painted over with yellow paint when assembling the originals. I have a few more sets of these, I wasn't planning on making a business of these, but I can send some out if people are looking for masks like these. I adhered the vinyl decals gently, and then taped off the rest, and hit it with some black spray paint:

So that's where it is now. I have some other parts for the internal switch setup that will be added to this thread once it is complete.


New Member
Part 2: Completing the build

The Van Oaks kit came with some cool little red domed LED covers, but looking at the original prop, I realized I had some flat-topped neon bulbs that I could saw off and use as a cover for a small 3mm red LED. I used this same technique when building my thermal detonator, as it also has that same style of flat red plastic bulb cover on the primary light (many replicas have a domed cover or bare 5mm red LED, but it should have the same flat cover). Mine is not exact, as the original appears to have some sort of grid texture, and is a little bit smaller, but it looks close.


Ratchet: One of the exciting parts of my plan was to give the twist knob a ratchet noise when it turned. First I tried to find something small with teeth inside, and ended up trying a bottle cap with a plastic flap. This failed. It was hard to twist, and the noise was dull, and then the tab chipped, as well as the soft bottle cap deforming into a not-quite-round-shape. I thought about it for another day, and then remembered those noise-maker ratchets from cheap new-years party stuff. I swung by the party store, and they had them for $1. The blue piece was a bit too long, as I would need the red handle to exactly line up with the center of the chamber, so I marked and glued the little flap in place with CA glue, and then sawed it off at the correct length.


The sound was perfect, a little twist made a great ratchet noise. I would find out after installation though, that in order to get a full ratchet sound of 4 o4 6 clicks, it needs to make a nearly full rotation. I needed to constrain the twist to allow for room for the battery, and to keep it from "over twisting" and breaking wires, and so with only a 120 degree rotation, it only gets about two or three clicks. Not ideal, but still more satisfying than silence. The red handle was cut down, and inserted with CA glue into the tube handle once the final length was determined. Regarding the brown shaft, it was a plastic tube, that I glued a dowel partway down and marked. This meant that the red handle could go in, but above that point, it would be more solid for the other parts to get screwed in to.

The Twist-Switch: My solution for a rotating switch was to have a sort of springy brass finger, that would rotate onto a curved contact plate. Both would have a small hole drilled in them, and a red wire soldered on to them. For this to work, I needed the curved contact plate to closely match the curve of the outside, to have a sort of curved lip to allow the spring to easily pop onto the plate, but also, it needed to be firm enough to maintain contact, but relaxed enough to pop back off. Not easy, but the bendable metal is tunable to get that result eventually. As mentioned before, the switch area needed to be contained so that it couldn't be over twisted, and would protect that zone from wires and allow for other parts to exist outside of the switch zone. The circuit is overall fairly simple:
9v battery > "twist-switch" > 330 Ohm resister > 3mm Red LED > 3mm Red LED > back to battery

Knob mount: Because I never fully trust glue when there is tension or stress of any kind, I wanted to ensure the knob wouldn't twist off from over-use. Once I determined the length of the rod on top, I drilled a tiny hole, and trimmed a small wire nail down to make a sort of spoke. Then I sawed the collar of the top knob to have a slot to match that spoke. Now when it was glued, the knob would maintain a firm mount that would not break from rotation stress:

Photomultiplier Tube Dynode: I mentioned I bought a pair of these original style greeblies from Wanna Wanga (the mirrored version), and they of course, look perfect because they are the same piece as the prop used. The pieces that were resin printed by VanOaksProps were nearly identical in size and shape, and would work well too, but I have always been fascinated by this greeblie, and was super happy to use it. One trick though, is they have very tiny holes that need to be enlarged. I found some very tiny flat head screws in my screw bin, and determined the new hole size required to get them just through without breaking the hole out. Using a drill press, I carefully enlarged them. To mount these delicate flat greeblies to a round surface was also a little nerve-wracking, but I checked with Wanna Wanga, and he said he just carefully bent them by hand. I did each screw a few turns at a time to help keep an even stress on all of the holes:

One thing to note, on some of the prop photos, there appears to be a sort of round hole in the main body of the grenade behind the vent. There is a round opening on the back of the dynode, and a very fine fabric mesh, but the strange thing is, you can see in the lower right photo, the reflection on the mirror-finish vent blades sort of creates the illusion of a black hole behind them (just like I saw in prop photos), even though there is solid beige plastic behind.

Next post: The completed prop!


Well-Known Member
cool stuff. can you tell me the correct tube for the photo multipliers for the bunker bomb build or a source for parts? I have a 3d print of the body. thanks.


Well-Known Member
How costly are the dynods things. I managed to get a tube, but got got the copper Vader helmet ones. Do I paint, sell trade?

Also, my vents are upside down if using for the bunker bomb. I read they can be taken apart. Any tips?
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Well-Known Member
Has anyone found an alternative to the knurled stereo knobs, besides a 3D print or resin cast?
Anyone know what field the wire clip thing was used in?

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