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Marshmallow Shooter Conversion

I call it, the Stefan Shooter

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#1 SPV999

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Posted 26 July 2009 - 05:31 PM

So, I was at TRU yesterday and saw this Marshmallow Shooter on sale for $12. I figured what the heck, if anything I could use it to actually shoot marshmallows.

It ended up being the simplest, yet most reliable and sturdy secondary I’ve ever built.

Here is the gun stock:

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The whole thing is powered by the forward handle. Ram it forward to fire, and pull it back to prime. The white PETG looking tube is where you load the marshmallow, it acts like a clip.

When you’re using marshmallows, it actually primes itself through suction, as the front barrel has a check valve that only lets air out and the end of the PETG has a check valve that only lets air in, sucking the next marshmallow into the barrel with the priming stroke. This doesn’t work with stefans, as they don’t fit tight enough and they are too heavy, but there are other ways to make it work...

The plunger head has an AIR TIGHT seal, almost unheard of stock anymore. You can literally plug the barrel and the end of PETG and you cannot move the plunger at all.

Now, we need to harness this power into NERF POWER!

First thing, disassemble it. The barrel comes off with a twist, and the PETG pops straight up (it comes off pretty hard).

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There is a small hole at the bottom of the where the barrel sat. This is where the air comes up from.

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CAREFULLY surround it in superglue and sit an O-ring on it. Just about any size would probably work, but I happened to have some #8 (9/16” OD x 3/8” ID x 3/32”) O-rings from my AT1k’s still lurking about.

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Once that dries, sand out the red hole in the back that connects to the PETG. You want the hole just big enough to fit a Stefan in smoothly, without a lot of extra space so it cant wiggle.

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Next, get your ½” CPVC coupler. The ones from Ace work better, as they are perfectly round and straight. I’ve noticed the ones that the Lowes’ near me sell are bowed in the center.

Drill a hole in the bottom of the coupler that lines up with your O-ring inside the gun. You’ll have to guess here, and guess well. Use another O-ring of the same size (they come in freaking 20 packs after all) to measure. The bigger you can make this hole, the better, but too big and it wont seal properly over the O-ring.

Mine’s probably a little under-sized but it works.

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Put some hot glue on the end of the coupler and slide it up against the back of the chamber, lining it up with the red hole, but at the same time pushing down on the O-ring. Give it 30 or so seconds to dry while pushing back and down on it. It’s very fragile right now, so I couldn’t get a picture.

Once it’s dry, fill the gap around the front with as much hot glue as you can.

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Now for the clip. Did I mention this has an 8-10 round (highly dependent on the size of your darts) clip? Well I did now. For the clip to work, you have to blow into the PETG to force the next dart into the barrel. However, as the PETG is positioned right now, it’s really hard to do so.

To fix this, take the PETG and superglue/epoxy a ½” CPVC elbow on the end. For this to fit on the gun, you’ll have to sand down that little nub on the very back end.

When you snap the clip on, be sure to push forward on it a little. It’ll usually go in an extra ¼” or so, and that makes a huge difference in terms of seals.

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Put a ½” CPVC barrel on the front end and that’s it!

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Ranges are very hard to pin. I have never seen a gun so drastically affected by dart weight, length, fit, and especially barrel length. The tighter the fit and the longer the barrel, the more pressure is built up and therefore the farther the dart will go.

What I can say is that using a 6” barrel I had on hand it gets pretty consistent 40-50” with my personal “top grade” stefans. I theorize it might get a little more with a longer barrel, but I dont have enough material right now to test it. Combine this with being able to put out 10ish rounds in a matter of seconds, and easy reloading, I reiterate that this is a solid secondary.... just don’t pass out from asphyxiation priming it....

If you think the clip is too much trouble, it works just as well without it. Use it as an ammo holder.


EDIT: Since there seems to be a little bit of confusion, I made a cheesy diagram of how the airflow of this gun works.

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1) Back handle
2) Front handle
3) Plunger, connected directly to the front handle
4) Plunger tube
5) O-ring I installed
6) PETG clip
7) Little red ring the PETG sits in
8) CPVC coupler
9) CPVC barrel

I forgot the elbow at the end of the PETG, but it’s not really important.

Airflow is thus:

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The air is forced forward as you push the front handle forward down the plunger tube. The PETG clip has a check valve on the end that wont let air out, so the only way out is through the CPVC barrel.

On the “priming” stroke

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Air is sucked back in from both the CPVC barrel and the PETG clip.

The stock gun had a check valve on the barrel that didn’t allow air in, so all the air would be sucked through the PETG clip, which would force the next marshmallow into the barrel. There is no good way to preserve this all-in-one action once converted to stefans.

However, by simply blowing on the end of the PETG clip...

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We can “manually” force the next dart into the barrel, regardless of where the plunger is in the plunger tube.

Edited by SPV999, 27 July 2009 - 07:19 AM.

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#2 Chris is cool

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Posted 26 July 2009 - 07:49 PM

I keep laughing at how many people had the same bed sheets as me when I was a child.

And, let me get this right, the elbow if so you can blow down the barrel easier to advance another dart?

Edited by Chris is cool, 26 July 2009 - 07:49 PM.


#3 spartan062

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Posted 26 July 2009 - 07:57 PM

Could you put up pics of it primed and such?
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#4 SPV999

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Posted 26 July 2009 - 09:10 PM

I keep laughing at how many people had the same bed sheets as me when I was a child.


But did you have a Lego Maniac pillow case?! *dun dun*

And, let me get this right, the elbow if so you can blow down the barrel easier to advance another dart?


Yep. Blowing on the elbow pushes the next dart into the barrel.

Could you put up pics of it primed and such?


In the last picture it's primed. The front handle is pulled back and there is a dart in the barrel (but, the barrel being opaque, you cant see it obviously). Fired, it looks exactly the same only the front handle is pushed forward.

Let me see if I can get a cheezy paint diagram up tomorrow.

EDIT: Digram in first post.

Edited by SPV999, 27 July 2009 - 07:18 AM.

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