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Big Bad Bow Overhaul

Reinforcement, universal coupler, and more!

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#1 Zorns Lemma

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Posted 28 May 2009 - 04:27 AM

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Goals of this mod:
- Coupler system to accept CPVC and PVC/PVC + nested barrel setups
- Attachment point for a removable linked breech
- More reliable plunger head
- Increased draw
- Reinforcements to handle 38+ lbs of draw force
- Air gun integration

I'm not going to bother with the introductory stuff like disassembling the gun and taking out ARs. There's plenty of BBB writeups you can follow. Furthermore, I've done this project over 2 BBBs, so the shell color you see will change.

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Reinforcements

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Let's start with the catch. Add epoxy putty to the catch plate and also the plunger rod:
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You want the catch nub on the catch plate to be enlarged enough such that the plunger rod has no horizontal "wriggle room"

I also found that my catch plate was loose in the catch well itself, so I added some epoxy putty to the guide ridges on the catch plate:
Posted Image
I only had to add the epoxy putty to the ridge that went into the side of the shell that contains the internals (right side, if the front of the gun is pointed away from you). To ensure the catch plate would still fit, I pressed the catch back into the well while the putty was still soft and used a knife to cut away the excess.
In the picture, you can also see how the addition to the catch nub is rounded on one side and more perpendicular on the other. The rounded side faces the front and allows for the plunger rod to still slide back under the catch.

Next, buff up on springs:
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I use McMaster part 96565K36 for all my catch replacement springs. I also had to buff up the trigger spring because I did a crap job cleaning putty off of the catch well so the catch was a bit sticky.

Finally, add a washer to the back of your plunger tube:
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I pushed the washer most of the way down, threw some goop on it, and pushed it the rest of the way in. The washer in question is a 9/16 SAE washer. Actual dimensions are 1-3/16" OD x 19/32" ID. This step serves two purposes. It creates a better force distribution on the back of the plunger tube because the steel won't deform as much as the bare plastic, and it also decreases the ID, allowing use of springs with smaller ID (like the +bow spring) without the spring twisting out of the plunger tube. Blacksunshine solved it by flaring his springs. This is my method.

Because of the smaller ID however, you will also have to shave down the corners of your plunger rod:
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Ignore the cut of peg for now.

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Improved plunger head

--------------------------------

Method 1: Improving the existing plunger head

Bend the "cup" shape of the plunger head backwards, wrap wire (or some other flexible round material) around the base of the plunger head, and add hot glue:
Posted Image
This expands the gasket which helps ensure a solid seal.

You should also cut off the top of the plunger head:
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Also, reinforce the plunger head by adding washers to the orange disc that compresses the springs. This has been done before, so consult b00m13 or Blacksunshine's writeups if you need help.

Method 2: Replacing the plunger head

Materials:

1.5" long 8-32x machine screw
1" long 8-32x 1/4" OD round aluminum standoff (threaded spacer)

Preparing the plunger rod

Start by cutting off the nub that holds the orange disc and plunger head and sanding the tip flat:
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Drill a 1/4" hole 1" deep for you standoff

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Take your 18-32x 1/4" OD aluminum standoff and epoxy that sucker in. Then add epoxy putty around it for extra support.

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The standoff is threaded for a 8-32 screw to screw on the plunger head.

Building the plunger head

Be sure to check out this post too, as it is both lighter and better sealing.

This step is an adaptation of the Longshot plunger head replacement. You want to sandwich a neoprene washer in between metal washers. Here are ideal dimensions:

- 1x 1-1/4" OD x 1/8" ID Neoprene washer
- 1x 1-1/16" OD x 1/8" ID Steel washer (back)
- 1x 1" OD x 1/8" ID Steel washer (front)

Here's what I ended up using, due a lack of materials at ACE:

- 1x 1-1/4" OD x 3/16" ID Neoprene washer
- 1x 1/2" SAE washer (1-1/16 OD x 17/32 ID)
- 1x #10 SAE washer (1/2 OD x 7/32 ID)
- 2x 3/4 OD x 5/32 ID steel washer
- 1x 1" OD x 7/16 ID fiber washer
- 1x 7/16 OD x 7/32 OD fiber washer

The first 3 steel washers create the "back" and the next three create the "front". I nest the washers by putting the smaller one in the larger one, and then glue both of them to the third for support and cohesion. The following two pictures should help enough:
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In the first, you can kind of see the third supporting washer hidden behind the front two through the hole.


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Expanding plunger tube/increasing plunger draw

--------------------------------


If you followed method 1 for the plunger head, you're going to want the white AR piece. Dremel it out fully, and bevel the inner lip a bit:
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Slap it over your plunger head:
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Bam! About .5" of increased volume.

If you followed method 2 for the plunger head you need to do absolutely nothing. The washers will be lying flush against the plunger rod, which gives you the .5".

Notice that method 1 requires expanding the plunger tube out; method 2 reduces the plunger rod in.

To allow for the rear section of shell to move enough for the extra draw, you may also need to dremel down the ridges in the front section of shell that run up along to the front sight. I don't have a picture of this, because you need to dremel down those ridges anyways for a linked breech, so I didn't think it was necessary for the plunger draw expansion. I've been informed it is.

Edited by Zorn's Lemma, 18 September 2009 - 12:32 PM.

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#2 Zorns Lemma

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Posted 28 May 2009 - 05:36 AM

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Universal coupler system

--------------------------------


This consist of an internal CPVC coupler and an external PVC one. If you followed method 2, you will also have the room for an internal section of PVC to act as a "coupler" for 19/32 brass.

Most 1/2" CPVC internal couplers take the CPVC coupler, cut it and then glue inside the orange cap like this:
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However, I prefer to dremel out the ridges, so that my coupler can rest like this:
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When cutting the coupler, and with method 1, be mindful of how much space you have. Ideally, the internal coupler will go to just where the plunger head rests:
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Be sure to leave yourself some room for padding also.

Affixing the internal coupler is easy. Drop it in, center it, and then fill the dead space around it with hot glue:
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Now cut a 1/2" PVC coupler in half and attach it to the outside:
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I center everything by running a piece of brass through (PVC around it to center in the PVC coupler):
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Now if you followed method 2, you will still have a lot of extra room from using 1/2 of a 1/2" CPVC coupler. What I did was take a section of 1/2" SCH40 PVC, and bored out a small section of it to fit 1/2" CPVC (the right side of the picture):
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Drop it through and hot glue it in. Depending on where you cut the CPVC coupler, you may need to dremel out a ridge so the CPVC can slide through:
Posted Image

Don't forget to add a darts stop! Also, padding (not pictured):
Posted Image

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Linked breech attachment point

--------------------------------


Take a rod of spare plastic and glue it into the rear section of the shell like so:
Posted Image
You will also need to dremel out the plate in that portion of the shell so the rod can fit. I used a section of pump handle from the SMDTG pump.

Cut the rod to a little more than an inch, 3/4" down, drill a hole and put in a 5/8" segment of metal rod or wooden dowel. I used a segment of a #6-32 screw. Now wrap etape around the base of the rod such that it has an OD of 1/2"
Posted Image
You can see how this system works. The CPVC used for the linked breech has the L slots cut on each side. Slide the CPVC over the attachment point, and then turn, locking it in place.

Edited by Zorn's Lemma, 28 May 2009 - 06:02 PM.

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#3 Zorns Lemma

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Posted 28 May 2009 - 05:49 AM

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Slide breech that accepts LS mags
--------------------------------


I'm going to assume you're familiar with slide breeches. If not, Angel and Tantum both have great writeups that you should familiarize yourself with first.

The breech consists of 6" of 19/32" brass sheath, 9" of 9/16" brass main barrel, 3/4" of 17/32" brass dart stop with 1/2" of 9/16" brass support, 5.5" + 3.5" of 1/2" SCH40 PVC housing and 4" of 3/4 SDR200 PVC support bracket.

There is also a 1/2" CPVC elbow, 1/2" PVC tee, and a small segment of 1/2" CPVC.

Picture first, to be followed by a lot of words
Posted Image

I wanted my breech to extend 1" into the plunger tube of the BBB. I'd need 1/2" of additional space for clearing the 1/2" PVC coupler, and then another 1/2" for mounting the 3/4" PVC.

This means that the first cut or base cut for the rear of the breech starts 2" up on the 19/32" brass, 1" up on the (5.5" section of) 1/2" PVC, and 1/2" up on the 3/4" PVC.

The BBB has a draw of 3.5". With a dart stop of 3/4" of 17/32 in 1/2" of 9/16 in the rear of the 19/32", that means the 9/16 main brass barrel will be pushed to a maximum of 4" forward of the end of the 19/32" brass. Since the first cut occurs 2" up the brass, that means I have room for 2" of dart slot in the 19/32 brass before sacrificing stability. The dart slot is simply a section of halfpipe cut into the brass. I cut myself 1.75" of dart slot in the pictures, but if I were to repeat this, I would go the full 2"

The LS clip is 3-3/16" long, so from the base cut on the PVC segments, cut up 3-1/4" to fit the LS clip. The cut in the 1/2" SCH40PVC should be a half-pipe, while being slightly less than a half-pipe in the 3/4" SDR200 PVC (probably 150 degree cut out, leaving 210 degress of the 3/4, which amounts to 15 degress on each side when centered symmetrically.)

Next come the cuts to fit the "wings" on the LS mag. These occur 11/16" up from the base cut and last 1-7/8". The cut is fairly deep on the 1/2" PVC piece, as you're only left with a 3/8" strip of material on top, which should fit between the slot in the wings of the LS mag. The cut is much more shallow on the 3/4" PVC, being only 5/16" deeper than the semi-halfpipe mark. The wings of the LS mag will go over the 19/32" brass, lie flush with the 1/2" PVC, and be held by the 3/4" PVC.

Here are pictures of the assembly process after all the pieces have been cut
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Wrap .5" wide of etape around the 1/2" PVC at the two ends of the magazine slot, such that it fits snugly in the 3/4" thinwall. Glue together. Then add your 19/32" sheath. Glue. These 3 parts together form the receiver.

From this point on it's very straightforward.

You want to sand down the 1/2" PVC at the front (marked with the etape in the pictures, but that excess etape shouldn't actually be there). You also want to sand out one end along the main line of the 1/2" PVC tee. Take your 9/16" main barrel and shove it into the receiver. Wrap etape around the exposed end of the brass such that it fits snugly in the 1/2" SCH40 PVC. Take your remaining 3.5" of PVC and shove it into the end of the tee that is opposite the one you sanded. Apply some glue to the etape. Take the PVC and Tee and shove it over the brass, such that the sanded end of the tee goes over the sanded end of the receiver. We sanded the ends earlier so that the system wouldn't stick at this point, thereby reducing stress on the linking mechanism.

Next, shove your CPVC elbow in to the open stem of the PVC elbow. You want it such that the distance from the center of the barrel to the center of the elbow is 1.75" This may require cutting the CPVC elbow if it doesn't fit, and creative use of the CPVC stub shoved into the cut ring of elbow, further shoved into the PVC tee for centering and joining purposes.

Finally, take 15" of CPVC, notch it so it can slide and lock over your linked breech attachment point, and assemble. Note that your length may not be 15" You want it short enough such that the breech fully closes when priming the BBB, but long enough such that the CPVC doesn't pull free of the elbow or tries to close the breech beyond the fully closed point.

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Pump integration
--------------------------------


I started with a BS pump. Cut it from the trigger, shove in some 1/8x1/4" vinyl tubing, superglue for holding strength, and then throw goop over that for seal. To fit it in the shell, I had to do some dremel work:
Posted Image
Also, drill a hole in the shell for the pump tubing. The amount of dremel work you need to do here will depend on the pump you're using.

Put the pump in and add liberal amounts of hot glue to hold it in place:
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Finished rear section of the BBB:
Posted Image

Now, we want to extend the pump handle. Cut yourself an 8" piece of 1/2" CPVC. This next step will vary depending on what pump you're using. With a BS pump, you want to cut the sides of the pump handle down such that it will fit inside the CPVC until you hit the part of the pump where it forms a +
Then, cut notches in the CPVC to fit over this +
Finally, drill 3/16" holes through the CPVC such that the holes also go through the holes where the old pump handle would attach.
Posted Image

Attach the two pieces together via a small amount of hot glue (physical spacing/prevents shiftiness) and 2 3/4" 8-32x screws and accompanying nut. I used 1" screws and then cut them shorter because I got a box of 50 assorted 1" and 1.5" 8-32 screws, so didn't feel like buying the proper parts.
Posted Image

Next, sand out a piece of PVC such that it'll fit over the CPVC.
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Glue this to the front sight. This will help guide the pump shaft.
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And make yourself a pump handle from 1/2" CPVC endcap inside 1/2" PVC elbow and a 1/2" PVC handle.
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Now we're ready for some integrations!
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Edited by Zorn's Lemma, 24 July 2009 - 08:53 AM.

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#4 DrSpaceman

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Posted 28 May 2009 - 06:52 AM

Thanks Zorn! Now I can get to work on mine.
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#5 Chris is cool

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Posted 28 May 2009 - 07:04 AM

My hat is off to you. This write-up is similar to Hereticorp's LS mod. It's lengthy, picture heavy, and gets to the point. I may very well do many of these things to my BBB. Have fun sprayin your friends up ;)

Edited by Chris is cool, 28 May 2009 - 07:05 AM.


#6 xbox180

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Posted 28 May 2009 - 10:39 AM

Amazing, I love the part that has the breech that can accept Ls/Recon Mags.

Best Write-up that I have seen in a while.
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#7 k9turrent

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Posted 28 May 2009 - 10:49 AM

It's prettyful
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QUOTE View Post

That's about it. And thanks Angela who helped me with these pictures.. It looks huge in her hands.


HOLY CRAP!

FU ALL

#8 Forsaken angel24

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Posted 28 May 2009 - 11:14 AM

Keep going buddy. I like where you are taking this.
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#9 mystefansdontflystraight

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Posted 28 May 2009 - 11:23 AM

I'm in the process of doing this. I started it when I saw your post in the mod/pictures thread. I need some kind of substitute for the SDR PVC because they don't sell it up here. Any advice? This thing looks Effeminate. Great job.
EDIT: I looked through my parts bin, and discovered that I had enough materials to do this:
Posted Image
I realize how much I need to cut the back down. IT will be done after school. Hopefully. I can't wait to see what that pump is for coming out the scope.
Thanks a lot Zorn! This is so useful.

Edited by mystefansdontflystraight, 28 May 2009 - 11:59 AM.

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QUOTE(Blacksunshine @ Dec 24 2009, 02:15 PM) View Post

QUOTE(white moonlight @ Dec 23 2009, 01:29 PM) View Post

It's just screaming to be rearloading...

I seen a movie about that once.



#10 veginator

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Posted 28 May 2009 - 11:37 AM

I'm in the process of doing this. I started it when I saw your post in the mod/pictures thread. I need some kind of substitute for the SDR PVC because they don't sell it up here. Any advice? This thing looks Effeminate. Great job.

It is also known as for thinwall or sch. 20 PVC.
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#11 xbox180

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Posted 28 May 2009 - 12:20 PM

Ranges?
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#12 Zorns Lemma

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Posted 28 May 2009 - 12:51 PM

Ranges?


Depends on the springs you put in. I'm running 4.5" of McMaster spring 9637k19 and an NF spring, both stretched to 5.5" and then retempered. The reinforcements are there to handle the 9637k19 with the 9637k26 (+bow), but I found priming the gun to be really annoying.

With the current setup, ranges are "pretty good" Good enough that I might switch to a 10" or 11" barrel, because the 9" just isn't cutting it.
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#13 Salmon

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Posted 28 May 2009 - 04:23 PM

I like how it was almost like multiple mini-writeups, so if someone isn't ready to completely overhaul their gun, they can simply choose some of the easier modifications. And I, too, am interested to see what you are going to do with the pump integration, though I'm pretty sure I have a good guess. :P
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#14 Zorns Lemma

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Posted 28 May 2009 - 06:26 PM

Thanks Zorn! Now I can get to work on mine.


:)

I'm in the process of doing this. I started it when I saw your post in the mod/pictures thread. I need some kind of substitute for the SDR PVC because they don't sell it up here. Any advice? This thing looks Effeminate. Great job.
EDIT: I looked through my parts bin, and discovered that I had enough materials to do this:
Posted Image
I realize how much I need to cut the back down. IT will be done after school. Hopefully. I can't wait to see what that pump is for coming out the scope.
Thanks a lot Zorn! This is so useful.


How stable is the LS magazine in your breech? The picture is a bit dark, but it looks like you had extra room for the LS mag to move around. However, I don't know your materials, so maybe it works well for you.

Also, over the weekend, I will be testing a plunger head with double the the neoprene washers, to see if that will work better.

Edited by Zorn's Lemma, 28 May 2009 - 06:26 PM.

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"In short, the same knowledge that underlies the ability to produce correct judgement is also the knowledge that underlies the ability to recognize correct judgement. To lack the former is to be deficient in the latter."
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#15 diamondbacknf1626

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Posted 28 May 2009 - 08:40 PM

So, so freaking cool. Very good work, and I love this writeup style, as do I hereticorp's longshot, and angel's doomsayer. Clear, concise, and well done. Pictures were taken with purpose in mind, and you pulled it off eccellently. This is a great example to all future write-up posters. Lookin good.

The gun's looking great. I can't wait to see some more.
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QUOTE(TxNerfer @ Nov 13 2010, 12:42 PM) View Post

Hey...I got a crazy idea: how about you stop all that sigging stuff? It's not even my thread and it annoys me.

#16 stuck by stefan

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Posted 31 May 2009 - 12:33 AM

What did you use to cut?
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#17 Zorns Lemma

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Posted 31 May 2009 - 03:15 AM

A rotary tool with sanding and grinding bits, a cutting disc, and a high speed cutting bit.

Really though, if you had to ask that question, you shouldn't attempt the mod(s) described.
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#18 stuck by stefan

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Posted 31 May 2009 - 01:14 PM

A rotary tool with sanding and grinding bits, a cutting disc, and a high speed cutting bit.

Really though, if you had to ask that question, you shouldn't attempt the mod(s) described.

I thoght it was a cut off wheel, but i asked because it looks cleaner than most cuts with cut off wheels.
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#19 Zorns Lemma

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Posted 24 July 2009 - 08:56 AM

I stopped by the McMaster warehouse and picked up some aluminum standoffs:

Posted Image

And figured since there's a war today, I might as well get my primary all the way done. Writeup is finished. Please excuse the shitty pictures, as I used my phone, forgetting to pack a camera.

Also, hotel showers make perfect places to go to town on PVC with a rotary tool, as the shower curtain and damp wall catches most of the dust that flies around.
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#20 Keith

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Posted 24 July 2009 - 05:36 PM

Since this topic is revived I'll go ahead and post this. Thanks for the write-up, man!

Posted Image

Posted Image
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#21 Zorns Lemma

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Posted 01 August 2009 - 09:00 PM

It's nice to see someone actually built one of these. How consistently does it shoot?

Anyways, I have a new plunger head design.
Posted Image

Parts are (from left to right in the picture):
- 1/2" SAE washer glued on top of 3/4 OD x 5/32 ID steel washer
- 1-1/4" OD x 3/16" ID Neoprene washer
- #8 SAE washer
- 1" OD x 7/16 ID fiber washer glued with 7/16 OD x 7/32 OD fiber washer
- 3/4 OD x 5/32 ID steel washer
- #8 lock washer
- #8-32 1" machine screw
Posted Image

The key is that you don't fill in the dimple created by the 1/2" SAE backed with 3/4". You place the #8 on the other side of the neoprene, and thus when the entire assembly is put together, the #8 forces down on the neoprene into that dimple, which helps form the washer into a nice cup shape, while the front washers maintain that shape.
Posted Image

This thus provides for excellent seal.
Posted Image
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"In short, the same knowledge that underlies the ability to produce correct judgement is also the knowledge that underlies the ability to recognize correct judgement. To lack the former is to be deficient in the latter."
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#22 Keith

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Posted 02 August 2009 - 06:23 AM

It's nice to see someone actually built one of these. How consistently does it shoot?


Well, I didn't do a great job on the clip but it's pretty decent with the breech when I use darts that fit just right and the follower doesn't hang up. I couldn't really tell you a number for the range. I mostly just use a cpvc barrel since that's what my current batch of stefans fits. But the fact that I could switch my barrels like that is part of why this mod is cool. I also like all the internal reinforcement, feels rock-solid.
It's not super consistent, from 80 to 100 feet (with cpvc) but it never gets terrible shots. I was having problems with the catch, but I fixed it by doing a bit of filing on the epoxy putty on the catch and putting 3 catch springs in.
It has the BBB (purple) spring, plus a Recon spring. I also just used the cut-down stock plunger head.

Edited by Keith, 02 August 2009 - 06:24 AM.

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#23 Zorns Lemma

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Posted 02 August 2009 - 06:07 PM

Well, I didn't do a great job on the clip but it's pretty decent with the breech when I use darts that fit just right and the follower doesn't hang up.


That's an easy fix. Sand out the notches on the follower that fit over the bars you put into your clip to make it stefan compatible. If you have further issues, PM me.
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"In short, the same knowledge that underlies the ability to produce correct judgement is also the knowledge that underlies the ability to recognize correct judgement. To lack the former is to be deficient in the latter."
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#24 2iko

2iko

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Posted 22 August 2009 - 09:54 PM

I'm having a hard time finding the ID of 3/4" sdr200 PVC if anyone could enlighten me? I know it's the same as sch 20 PVC but I couldn't find that either. I need this because I'm looking on McMaster.
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I have no sig so my posts cut off weird so I'm putting this here. XD


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