NerfHaven: Nerf Stampede "Brass Breech" Mod Guide! - NerfHaven

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Nerf Stampede "Brass Breech" Mod Guide! - 100% Air Seal -

#1 User is offline   SgNerf 

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  Posted 25 January 2012 - 10:27 AM

This mod guide will look into my "Brass Breech" modification for the Nerf Stampede.

--

Introduction:

The stock stampede plastic breech does not have an air-tight bolt to barrel seal, hence the plastic bolt itself is essentially the barrel. Once the foam dart is fired out the bolt, the foam dart already starts losing power and velocity. In addition, most of the air pressure from the plunger is wasted once the foam dart leaves the bolt.

For those new to the brass breech concept, the design objective of an air-tight brass breech system is to create a 100% air-tight seal all the way from the plunger through to the barrel, thereby providing efficient air pressure delivery to propel the foam darts further. This would result in more power within each shot, with greater firing distance and faster dart velocity.

For a stampede brass breech to work, it requires the air-tight connection of matching brass tubes and a guide cover to ensure that all the moving parts are aligned properly.

My design is optimized to work with stefans (short length customized foam darts), although it could be adapted to use normal length foam darts, they usually wouldn't perform as accurately or consistently, and may result in much higher rates of jams.

The following guide will cover my customized version of the "Brass Breech" mod.


Credits:

My brass breech design for the stampede is based on the excellent "PVC guide cover" design by Oxymoron at the OzNerf forum, full credit goes to him for that design.

Link to the original "Oxy's stampede Breech" thread by Oxymoron at the OzNerf forum.


Important Note:

The "Brass Breech" mod is a more advanced mod project that should only be performed by those who are already familiar with modding the Stampede.

For new modders, please refer to my Nerf stampede Mod Guide to get familiar with the modding basics first.

Disclaimer: Modify at your own risk. Modifications may wear out or damage your blaster. Please be careful when using hobby tools!


Lets start...

Step 1: You will need to obtain 3 different sizes of brass tubes (Brand: K&S Engineering) and a suitable PVC pipe for nesting them into.

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The brass tube sizes are: 1/2", 17/32" and 9/16". All of them are 0.014" wall thickness. They are usually supplied at hobby shops in either 1 ft or 3 ft length tubes.

I use a 13mm SingaPlastics brand PVC pipe which can nest the 9/16" brass tube. This pipe will be used to create the PVC guide cover.

For modders in the USA, SCH40 1/2" PVC pipe might be a substitute, i think it could be possible to adapt it to work with this design.

Note that the inner diameters (ID) of PVC pipes often tend to have variations, even within the same length of pipe, so you have to test different sections and make sure it fits the brass tubes before usage.

Its recommended to prepare and polish the brass tubes with some metal polish to remove any oxidization that may have occurred both externally and inside the tubes, this helps smoothen out the surfaces for lower friction and better fit.

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As you can see, the brass tubes nest perfectly within each other and they all form an instant 100% air-tight seal. Those who have worked with brass breech systems will be very familiar with this unique characteristic. :)


Step 2:

Lets start with the PVC guide cover, this is the most essential part of the stampede brass breech system. The guide cover ensures that the moving brass bolt chambers each foam dart into the barrel properly and consistently.

Take the PVC pipe and mount the N-Strike clip on it.

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Use a marker to trace the outline of the clip's shape.

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Use a Dremel with cut-off wheel to cut out the traced lines.

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As the top section of the guide cover ends up being a rather thin strip of PVC (which will tend to flex too much), i cut out another shaped part from a larger 16mm SingaPlastics brand PVC pipe which is then glued on the top to further reinforce and stiffen that section.

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The PVC guide cover is done!


Step 3:

Now we proceed on to the brass barrel section.

In my example, i use a 21 cm length (8+ inch) of 9/16" brass tube as the barrel. It is nested and glued into the PVC guide cover.

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Use a Dremel with sanding bit to bevel the inner edges of the brass barrel, this creates a funnel design to enable smoother chambering of the foam darts and brass bolt.

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I positioned the barrel and guide cover assembly to align with the internal dimensions of the Stampede, an additional PVC pipe was nested at the front of the barrel to help keep it in line with the Stampede's front casing structure piece.

The orange collar piece is also positioned and glued to the PVC guide cover to establish a fixed securing point to the blaster casing.

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The brass barrel section is done!


Step 4:

Next we proceed to the brass bolt section.

Use a pipe cutter to cut away the stock plastic bolt, as shown in this photo.

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To make the brass bolt parts, use a Dremel to separately cut out a set of brass tube sections in the following lengths:

1/2" brass tube: 11 cm
17/32" brass tube: 2 cm (2 x spacer sections)
9/16" brass tube : 9 cm

These are my custom tube measurements for the stampede brass breech system.

These measurements need to be as accurate as possible. Any variations may affect the overall structure and air seal of the breech system.

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Used a Dremel with sanding bit to bevel the outer edges of the brass bolt front section, this will help to further enable smoother chambering of the foam darts and brass bolt into the brass barrel.

Here is my Nested Brass Tubes Cut-Away Diagram:

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Nest the assembled brass bolt into the plunger casing.

Use the strongest glue you can get to glue everything together. I use "Selleys Super Strength" 2-part slow-curing epoxy glue (curing time of 3 days!). Make sure the glue cures completely for maximum bond strength.

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Note that the 1/2" brass tube acts as the air channel and helps to reduce dead space, but not too much to create an air restriction.

The 17/32" brass tube will chamber the foam dart and connect into the 9/16" brass barrel, this is what creates the 100% air seal.

The brass bolt section is done!


Step 5:

Sleeve the brass bolt into the PVC guide cover. Test the parts movement and connection with the brass barrel.

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The brass bolt must be able to move smoothly within the PVC guide cover without resistance.

If there is resistance, use a Dremel with sanding bit to widen the inner diameter (ID) of the PVC guide cover until it fits.

When the 17/32" brass bolt connects into the 9/16" brass barrel, it should have a 100% air-tight seal. Test the seal by closing the breech, then manually compressing the plunger while blocking the barrel exit, there should be resistance felt in the plunger rod.

Next, install all the parts into the Stampede.

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Test the parts fit and test the movement of the brass bolt. Make sure everything moves smoothly.

If there are parts which encounter resistance, either loosen or trim the fit and test again.

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Assemble everything together, keep testing the movement of the parts as you assemble the blaster.

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Its completed!

Here are some close-ups of the breech system:

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Awesome!


Stampede Brass Breech - Demo & Test Fire Video:




Sample Test Fire Results:

PTG: Parallel-To-Ground (Shoulder height, no elevation)
ATG: Angled-To-Ground (Aimed higher, 30 degrees elevation)

Distance is measured at where the dart lands (Average of 6 darts).

Brass Breech Stampede (9kg Load Spring)
Ammo: Customized FBR foam + 1.1 gram soft silicone tip weight
PTG = 95-105 ft
ATG = 120-130 ft

Note that the test was done indoors with customized foam darts and the results are sample estimates for reference (your results may differ depending on materials and mod techniques used).


Important User Tips:

- Short length customized stefans work best with this breech system, make sure that the stefans used are in perfect condition and fit the brass barrel properly (not too narrow or not too wide). In addition, ensure that the back portions of the stefans are rounded without any excess foam sticking out which might get clipped by the brass breech when it closes. Taking care of these various factors will greatly reduce the chances of jamming.

- With the clip and trigger locks removed, do not put your fingers into the breech section when the blaster is in operation, as this can result in injuries.

- The better the foam dart fit in the brass barrel, the better the range results.


Variants:

For fans of minimized Stampedes... check out the brass breech mod done on my "SMG" Variant!

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Note the extra length of PVC pipe and coupler covering the brass barrel in front, it is designed to cover the brass tube edges for safety in Nerf games.

This post has been edited by SgNerf: 08 May 2012 - 07:37 AM

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#2 User is offline   Pause 

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Posted 25 January 2012 - 10:45 AM

This is too cool. ToT
Thank you SG. Thank you so much.
-Pause-

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View PostDaniel Beaver, on 24 October 2012 - 10:56 AM, said:

Heh.

USER WAS BLAND IN THIS POST

#3 User is offline   zx532 

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Posted 25 January 2012 - 12:25 PM

That's awesome, thank you so much

Before ripping my stampede apart though, do you think the design could be modified to fire standard darts just by increasing the pipe size?
Progress: Just a long line of people saying "See? I told you it could be done"

#4 User is offline   gehaga 

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Posted 25 January 2012 - 12:58 PM

SgNerf, you never cease to amaze me. You're a wizard I swear.

View PostDraconis, on 15 June 2012 - 04:10 PM, said:

Send me a PM with your address, credit card info, a scandalous picture of your mother, and your social security number. Okay, I'm kidding about the social. And the credit card.

#5 User is offline   andtheherois 

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Posted 25 January 2012 - 01:32 PM

This is amazing. When i first tried my stampede brass breech I did something similar with 1/2 PVC. However some modifications need to be made in order for it to fit. The biggest obstacle was getting it perfectly centered, since I had to widen the bolt tooth chamber. Would you be able to give us specific dimensions of your pvc? I'm sure we could find something in Mcmaster.

Edit: looking through mcmaster, I found this: 8628K57 9/16 Id, 5/8 OD nylon tube.

This post has been edited by andtheherois: 25 January 2012 - 01:47 PM

The YooToobz
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Gears said:

Winning rounds is rewarding, deal with it. We don't play fucking patty cake over here.

#6 User is offline   SgNerf 

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Posted 25 January 2012 - 02:02 PM

View Postzx532, on 25 January 2012 - 12:25 PM, said:

Before ripping my stampede apart though, do you think the design could be modified to fire standard darts just by increasing the pipe size?

I guess its possible to widen the breech gap just enough to fit standard length foam darts, though it requires even more precise tweaking of the measurements to get the fit just right.

Note that the bolt movement is only approx. 7-8cm, which is a very narrow tolerance for a brass breech system to chamber longer foam darts and also have the brass tubes nest securely to create the necessary air-tight seal.

But if you do manage to successfully make a version what can chamber and fire standard length foam darts consistently and reliably, do post it up too. :)
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#7 User is offline   SgNerf 

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Posted 25 January 2012 - 02:18 PM

View Postandtheherois, on 25 January 2012 - 01:32 PM, said:

This is amazing. When i first tried my stampede brass breech I did something similar with 1/2 PVC. However some modifications need to be made in order for it to fit. The biggest obstacle was getting it perfectly centered, since I had to widen the bolt tooth chamber. Would you be able to give us specific dimensions of your pvc? I'm sure we could find something in Mcmaster.

Edit: looking through mcmaster, I found this: 8628K57 9/16 Id, 5/8 OD nylon tube.

The 13mm SingaPlastics PVC pipe i used have an ID of approx. 14mm and an OD of approx. 18mm... yeah, the printed spec labels on those PVC pipes rarely correspond to their exact dimensions. :mellow:

The nylon tube dimensions you mentioned seem to be a good fit, the OD is a few mm narrower than the pipe i used, so it should just be a matter of wrapping some e-tape or creating some spacer rings to adapt it to the stampede internal parts and casing.
Nerf News & Reviews! >> http://www.sgnerf.blogspot.com
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#8 User is offline   7to9pounds 

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Posted 25 January 2012 - 02:56 PM

I just crapped myself.

This post has been edited by 7to9pounds: 25 January 2012 - 05:09 PM

Nerf in Arizona? pm me

#9 User is offline   Daniel Beaver 

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Posted 25 January 2012 - 02:57 PM

Jesus has come back, and he's a toy gun now.

#10 User is offline   Funky Mutha Facko 

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Posted 25 January 2012 - 03:43 PM

Langley Edit: More like Fucking Image Mackro amirite?

With those ranges and rof, I can't even think of anything else that comes close.

I'm just blown away.
HARDCORE NERF!

#11 User is offline   BillyBones 

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Posted 25 January 2012 - 04:58 PM

Quite possibly the best mod I have ever seen!!!

#12 User is offline   arfink 

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Posted 25 January 2012 - 04:59 PM

All the noobs (correction, every single nerfer ever) will want one, and all the war moderators will have to ban them. Totally awesome!
A2GS + 4 meg RAM + 128 meg CF + 9600 Baud Lantronix = WIN

#13 User is offline   Guitarzan 

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Posted 25 January 2012 - 05:35 PM

That is soooo sick SG. I think it's especially creative that you cut the clip shape out of the original barrel. I want one.

#14 User is offline   blitz 

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Posted 25 January 2012 - 05:50 PM

This is boss.
A sig should be like a woman's dress, long enough to cover the subject, yet short enough to be interesting.

Actually, maybe it shouldn't cover anything at all.

Blitz, member of the FNBS
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#15 User is offline   Curly 

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Posted 25 January 2012 - 06:32 PM

How have the Stampedes with 9KG springs been holding up? Are you getting a full 9KG from the spring? With this combo and 16.8V listed are you experiencing the overheat or the risk of overheat? Anyway, I've soiled myself...thanks for that.

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