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Project Highlander


CatgutViolin

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I printed out some graph paper at work a few days ago and spent my lunch break doodling and revising some basic plans. Some parts on this are obviously very rough, the main point of the diagram is to have plans for the frame assembly (which is to scale- each square is 0.5"). The construction will be three layers of 0.5" MDF, with the triggers, latch, and other small parts build from 0.25" MDF and superimposed as necessary. The main thing not on the diagram is the stock, which will be a Mossberg wood stock that I should have access to next weekend. I have never worked with MDF and have some concerns regarding its durability, but I plan on reinforcing the trigger mechanism with brass or aluminum sheeting bent to shape to form a frame and help the pieces resist deformation.

This weekend I will be doing basic prep work. Next weekend I will have my Dremel, drill, and vice, and the real work starts. This is going to be a marathon project to get it done by the deadline.

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I can't even imagine how is it supposed to be made of MDF. Some sheet plastic would be much better, more rigid and resistant to weather. I used 3mm polystyrene for my "cyber ninja sword handle" project and it worked perfectly (plus, it's easily glued using model glue, Revell's Contacta glue managed to hold polystyrene and EVA foam together despite tension caused by the wrap-around design).

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I can't even imagine how is it supposed to be made of MDF. Some sheet plastic would be much better, more rigid and resistant to weather. I used 3mm polystyrene for my "cyber ninja sword handle" project and it worked perfectly (plus, it's easily glued using model glue, Revell's Contacta glue managed to hold polystyrene and EVA foam together despite tension caused by the wrap-around design).

I came to the same conclusion when doing some structural testing the other day, so I got a few sheets of 0.25" (6.4mm) sheet styrene and will be using that instead. I'm a big fan of styrene sheeting as a material- it's easy to shape, easy to sand, doesn't deform under stress (unlike the MDF), takes paint well, and forms indestructible bonds when glued. The main obstacle is really just the price ($35 for just 24"x24"- ouch), but I figured better to get the right materials and do it right the first time. If the stuff was cheaper, I'd use it for everything!

 

So, on Saturday I began a small test of paint method on some scrap PVC, and the results came out way better than I expected. I've always had problems with paint chipping on my creations, and nothing ruins the realism of a prop more than ugly white plastic showing through the paintjob. I was especially concerned about PVC, which has a reputation for not taking paint well. Well, after a bit of research, I found that high-temperature barbecue paint comes recommended for painting gun props, so I thought I'd give it a shot.

 

Here's the overall process I'm going to use. The only part not on the sample below is the very last step.

-Sand thoroughly with 120 grit sandpaper, to give a good surface for the paint.

-Spray with Rustoleum High Heat Black.

-Sand with 200 grit sandpaper.

-Spray again, a little lighter.

-Sand with 400 grit sandpaper.

-Spray again, very lightly, just enough to solidify the color.

-Buff to a gentle shine.

-Rub with graphite. I took some graphite from a mechanical pencil and a small piece of sandpaper, and sanded it down to a small pile of the stuff. I then rubbed it onto the piece with a wadded tissue until I had full coverage, then rubbed it hard with clean tissues until no more graphite came off.

-(Not in picture) Spray with semi-matte sealant. This should cut down on the shine to give a more realistic look, while still allowing some of the metallic tone to come through. I didn't do this on account of not having my spray paint while I'm away from home.

 

So, aside from that last step, which will dramatically cut down the shine, here's the result.

 

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Most important, though, was the durability. Well, even though it's not fully cured (generally takes a week, sometimes two, for most enamel paint to be 100% cured), I am very pleased. Scratching it with my thumbnail doesn't take off any paint, just the layer of graphite, which is only noticeable because the paint is less shiny. I had to scrape it with a knife to get any of the paint to come off, and even then it was minor. I'm calling this a success!

 

Next, here is the barrel assembly, all purple'd up. The purple, for those who don't know, is a priming solvent used for PVC. It eats into the PVC, dissolving away the top layer of protective plastic and finish, allowing glue to secure a stronger bond. For my purposes, getting rid of that top layer makes it easier to sand and helps the paint adhere.

 

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And lastly, a word on ammunition. I have ordered a six-pack of Matrix Eagle Force 40mm grenades from Evike, and am looking forward to seeing how they perform on CO2, as an interesting guide recommended them. However, one thing I want to try working on is the ammunition, as firing footballs is my primary use for this gun.

 

In real life, the Minie ball was developed in the early 1800s as a way to drastically improve musket accuracy. It's a conical projectile that had a flared base, allowing it to be muzzle-loaded easily, but still expanding to fit rifling when fired. What a lot of people don't know is that the design of the projectile itself also improved accuracy. The conical design keeps the weight forward, but still retains enough aerodynamic surface to correct any tumbling in-flight, like a shuttlecock. This effect is also used in airgun ammunition, and modern tank rounds. I believe that by improving the tail surface of a pocket football, which normally provides the same function to a degree, it may be possible to strengthen this effect.

 

The implementation I want to test is using a length of plastic flagging tape to form a tail not unlike that of a kite. The tape, which I have ordered in bright orange coloration, will wad up between the shell and the football in the barrel. When fired, it will serve the dual purpose of acting as an aerodynamic surface (imparting drag to stabilize the projectile) and an additional visual cue to highlight it in flight, as often players don't realize they've been taken out by a rocket.

 

I have no idea whether it'll work or not, but I figure it's worth a shot. Like I said before, this weekend is when the real fun begins.

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I came to the same conclusion when doing some structural testing the other day, so I got a few sheets of 0.25" (6.4mm) sheet styrene and will be using that instead. I'm a big fan of styrene sheeting as a material- it's easy to shape, easy to sand, doesn't deform under stress (unlike the MDF), takes paint well, and forms indestructible bonds when glued. The main obstacle is really just the price ($35 for just 24"x24"- ouch), but I figured better to get the right materials and do it right the first time. If the stuff was cheaper, I'd use it for everything!

Yeah, it's pricey, I remember paying half that for a 0.5m x 0.5 m sheet of 3mm styrene, and 6mm cost around $35 over here as well. Also, IIRC our resident genius RenegadeCow works with styrene too.

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Update time!

First, I had to cut my two sheets of styrene into usable slabs. Each is 0.25", but the core is intended to be 1.5" wide, so I needed six sheets there, plus another two for paneling and details, so eight 12"x6" sheets it is. Cutting straight lines with a jigsaw requires clamping wood as a guide, a time-consuming and laborious process...

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...but the results are well worth it. This is the cut side facing the camera.

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After cutting them all in half again to get eight panels from four, I clamped four panels together to make the outer walls. The design here is very simple- two outer walls, 0.5" each, each composed of two 0.25" panels, sandwiching an inner layer containing all the moving parts. I've roughly cut out the outline with a hacksaw (the jigsaw likes to wander and bend on parts this thick), and I'll be attacking it with a Dremel before assembly.

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Here's a mockup of the gun. I'm going to need to experiment as it comes together to see whether the 'hump' right in front of the stock is going to cause problems with reaching the triggers, but I can always shave it down if need be. Still not sure if I'm going to square off the top, or see if I can shave it down into a rounded top (like the China Lake Grenade Launcher or Browning A5)- collective input is always appreciated. I also will likely include a handguard extending forward of the hinge point, as per the initial diagram.

I'm also set on sanding down the stock and refinishing it. That wood finish does nothing for me.

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Lastly, I carved out the barrels with my Dremel, and cut out extraction channels with a cutting wheel. Extracting spent shells is a piece of cake and they slide in and out freely.

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This was all about two hours of work, hopefully I can dedicate most of tomorrow to getting as much done as possible. All comments appreciated.

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Why I'm not a fan of styrene myself: the cost. I stick to PVC, cheap but a bit harder to use and needs extra precautions when handling. For paint that sticks on plastic, I use acrylic epoxy. Or you can use specific primers for plastic by Krylon. Regarding the ladder sight, you need to make the front sight as high as AR sights (starting from the rail) if you're to use M203 leaf sights.

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Why I'm not a fan of styrene myself: the cost. I stick to PVC, cheap but a bit harder to use and needs extra precautions when handling. For paint that sticks on plastic, I use acrylic epoxy. Or you can use specific primers for plastic by Krylon. Regarding the ladder sight, you need to make the front sight as high as AR sights (starting from the rail) if you're to use M203 leaf sights.

 

I was wondering how long until you'd comment here, since you seem to be the king of homemade grenade launchers (I'm super excited for that China Lake, by the way, whenever ICS gets around to it). I considered sheet PVC but it seems to be the same price as the styrene around here- how does it compare physically? Thanks for the advice on paint, but given that the test I did seems to be more or less indestructible I think I'm gonna stick with what I know, even if it is a bit of a laborious process. At this point I'm thinking I might be able to fashion my own ladder sight after all, since using the Dremel cutting wheel on the styrene is turning out to be a lot easier than I'd feared, it's just going to be a bit of work to fashion a spring-loaded hinge mechanism but I have a few ideas on that point. First priority is to just get the body together and the basic mechanism functioning, then the bells and whistles can come later.

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Well, it's gettin' there! There's been a slight setback as it turns out the wooden stock has a stupid design that means I need a foot-long screwdriver to take it on or off, so I'm going to have to use a different (synthetic) stock for the time being, but the internals are all roughed out (just need to be filled and sanded), the firing mechanism works, the hinge is all set, and the body is held together quite durably by screws.

I know it's looking EXTREMELY rough right now, but that's the beauty of styrene- it's very easy to shape and adhere. The firing pins, for example, started life as two rectangular blocks. I used a Dremel to sand them into octagons (30 secs), then sanded by hand to make them round (2 mins). Once the gun is all together I'm going to alternate sanding and gap-filling until the whole thing is one big, smooth piece. That goes for the internals too.

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I haven't been able to post progress all week, I take it the forum's been down?

 

Anyways, I have a lot of progress. As in, I finished the project. First, Mike, that was something I considered, but I figured the spring on the grenade valve is good enough and the rounded wedge on the frame underneath the lower barrel is designed to move a protruding firing pin out of the way, so there's no risk of smashing a firing pin when loading or unloading anyways, and considering how tough some grenades can be to fire I decided there was no point in extra tension on the trigger.

 

So, pictures! I'll be getting better ones for the official submission. Maybe do a video of ammunition testing tomorrow, since I have done some work on building a better rocket. These are in chronological order, showing the build progress.

 

A few notes on things I did while building:

-The triggers were reinforced with brass sheeting, bent to shape and wrapped around. This gives them durability against bending, which was my main concern from a durability standpoint.

-The ladder sight folds down, but it's back, not forward like on an M79. I figured if I run into something I want the ladder to fold rather than break, so this seemed the most logical choice.

-The front sight is based on an Enfield front sight. The barrel break latch has two vertical prongs that allow it to double as a rear sight for direct fire.

-The paint is as detailed in my first post, except with the matte spray (Testor's Dullcote) at the end. I'm very pleased with how this method turned out.

 

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All questions, comments, etc greatly appreciated!

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Pretty cool! Though I imagined you doing the foregrip in wood.

I've been toying with the idea. I originally went with the metallic tone because my direct inspiration was the China Lake grenade launcher, but I might go back and give the grip a wood paintjob. At the moment I don't have access to my painting supplies though, so either way it'll have to wait.

 

I think this is basically the definition of 'last minute entry' at this point.

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