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Big Bad Bow - Replaced Internals

Level 4 mod by crossbow conventions

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#1 Zorns Lemma

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Posted 26 January 2010 - 08:44 PM

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I apologize for the lack of assembly and completed gun photos. Most of these were taken in-progress during mod parties, which is great for the writeup; however, photos and a video of the final product were lost somewhere. This blaster was done as a contract and already shipped, so it is up to the client to post final pictures to help convey what words cannot. Also in this vein, a lot of my pictures will be misleading, as they were indeed taken before final refinements. Pay attention to the captions.

Materials
  • 12" section of 1-1/2" sink drain extension pipe
  • 1-1/2" OD rubber washer
  • 1-1/4" OD steel washer
  • 1/8" plastic sheet (I used PVC) #8747k112
  • 1/16" plastic sheet (I used PVC) #8747111
  • 12"+ of 7/16" square plastic rod (I used 1/2" square polyethylene rod and shaved it down...) #8732K14
  • 6-32 machine screws (various lengths)
  • 6-32 threaded rod (4" piece or longer)
  • 1/2" 6-32 set screws #94025a400 or #92311A148
  • 6-32 nuts and wingnuts
  • stronger catch spring #96565K36
  • #9637K25
Also, you will want a saw (I guess cutting wheel works too) to cut/machine plastic, a drill with 7/64" or #35 bit and a 1/8" or slightly larger bit, and a 6-32 tapping bit.

Preparing the Shell

Sand down all the ridges in the rear portion of shell up to the very large ridges that hold the vertical fins of the plunger rod.
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You want your 1.5" sink drain to be able to fit nicely within the rear section when assembled.

Constructing the Plunger Tube
Start by cutting yourself 6.5" of sink drain pipe, starting from the front.
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Build a spring rest by cutting a (1-1/4"?) circle out of 1/8" plastic sheet. In the picture I used 1/2" plastic sheet. 1/2" plastic sheet is complete overkill. Before you have completely detached the circle out of the plastic sheet, drill a 1/2" hole in the center. then finish cutting out the circle. This is easier than completely cutting out the disc and then drilling a hole in it, and I prefer it to pre-drilling the hole and cutting out the circle in case you cut your circle crooked/off-center. Err on the side of a larger disc than a smaller one; you can take a sanding drum to the disc later to get it to fit perfectly inside the sink drain. Dry fit the pieces together, and secure with a few dabs of superglue, and then drill + tap 4 1/2" deep 6-32 holes equally spaced around for your set screws.
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You'll notice that I have also taken the liberty of solvent-welding the spring rest into the plunger tube. This is also excessive, as the set screws will be enough to hold the spring rest against any reasonable amount of springs put in there. However, as the front bushing is removable, there is no harm in doing so. However, you may want to make your front bushing permanent for whatever reason, in which case you will want your spring rest to be removable.

The front bushing is constructed out of a 3/4" to 1/2" slip reducing bushing, solvent-welded inside the rear piece of 1/2" sink drain tail (fron the scrap piece you cut off when you shortened the plunger tube). Sink drain extension is designed to be fluted so the rear end can fit into the front end of the next piece. Depending on the specifics of the tube you buy, you may need to sand down the bushing to get it to fit. You want a long enough piece of scrap sink tail to fit snugly into the plunger tube and also enclose your bushing. Also, add padding at this point for your plunger head.
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Because I lost my original piece of sink drain, I had to substitute, which is why in the following pictures, you will see that my front bushing is severely sanded in, and is not fully enclosed in sink drain tail.

Fit the bushing into the plunger tube and drill/tap a hole straight through. You should place this hole about 1/8" further back than I did.
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The fit is supposed to be like this
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but you can see that sink I drilled my hole too far forward, the bolt that is supposed to run through the shell and the plunger tube and the bushing, securing everything together, is not going to have enough plastic to latch on to. Thus, I had to move everything in my assembly 1/8" back, which puts additional constraints on spring compression, and also reduces draw length slightly.

This is how the plunger tube is supposed to look with the front bushing attached.
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Notice that my bolt use is way too short as it is supposed to extend out long enough to be visible (and thus securable through nuts) on the outside of the front portion of shell.

Preparing the Shell, 2.0

Make the front portion of your shell look like so
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The rear ridge is dremeled out completely so that the rear section of shell can push forward as much as possible (increasing draw). The front ridges are dremeld down to fit the OD of 1.5" sink drain. The green dot is the hole to fit the bolt that secures the plunger rod. To drill this hole, I place the plunger tube into one side of the shell and drill down through the visible portion of the plunger tube into the shell. Then I run a bolt through this half of the shell and the PT, add super glue to the other side of the PT, and press down the other section of shell. I remove the bolt, remove the already drilled section of shell, and then run the drill through the plunger tube and the other section of shell. This ensures that your holes in the shell match up with the holes in the plunger tube so that your bolt will fit nicely through. Also, drill these holes with a larger bit as you won't be tapping them.

Constructing the Plunger Rod

Start with 13" of the square rod. 12" may do if you are buying 7/16" square nylon from McMaster rather than 1" square rod or 7/16" square rod from a different plastic supplier. Notice that in the picture the square rod is less than 12"; this is because of mistakes in previous steps that required me to cut it down to size. However, you want more starting material than less, which is why 13" is preferred.
Shave down the height of your square rod if needed. One of the cross-sectional dimensions must be 7/16" or slightly less; the other doesn't really matter, though it should probably be 7/16" or greater. Cut a catch notch in your square rod. You can use the picture for reference, but it is best to measure carefully against the stock plunger rod. Measure from the back (the end opposite the arrow, in the direction of the arrow), as you will have to slowly cut down the front to get everything to fit in the end.
Also cut a 1/16" wide slit for the horizontal fin. Again, you can use the picture for reference, but carefully compare with the stock plunger rod, and measure from the back. Getting the spacing right here is crucial. To cut the slit, I drilled successive holes and then connected them all together with a cutting disc. Depending on what material you use, your mileage may vary. Polycarbonate and PVC rod will be easy to machine: you can just drill the endpoint holes and cut the slit out with a saw. Nylon and polyethylene will be annoying to machine, if you want to cut the slit with a saw, you will have to be extremely patient.
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Next, cut a fin out of 1/16" plastic sheet. Use the picture for reference in dimensions, but again, compare frequently with the fin of the stock plunger rod.
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Drill and tap two holes to secure the fin.
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The fin will be secured with two sections of 6-32 threaded rod, which will double as the vertical support. You are probably better off repeating this process to cut out a vertical fin as well and solvent-welding it together. I was both lazy, and chose to go with ease of disassembly, so as reassembly is also easier.

Finally, drill and tap a hole in the business end of the plunger rod to secure your plunger head.
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The plunger head is constructed from a 1.25" steel washer as the spring compression piece, a 1.5" rubber washer to seal, and a 1" washer cut from 1/8" plastic to help form the seal. The sides of the plastic washer are beveled to help the rubber washer form a cup shape.
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The plunger rod is assembled like so. Notice the stubs of threaded rod securing the fin. Also, notice the lack of a lock washer on the front. You would do well to add one. You can also see the beveling on the plastic washer.
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Edited by Zorn's Lemma, 27 January 2010 - 04:52 AM.

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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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#2 Zorns Lemma

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Posted 26 January 2010 - 08:47 PM

Reinforcing the Catch

Cut a section of 1/16" plastic sheet and solvent-weld onto the catch like so.
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You will also want to buff up the sides of the catch with epoxy putty. Score up the catch so that epoxy putty will adhere better, and then just apply a liberal amount to the sides. Press into the catch well on each side of the shell to form the epoxy putty, and then scrape off the excess. I don't have a picture of this on the current catch for this project, but I drudged up a picture from my original 3B overhaul writeup.
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You will also want to buff up the catch spring. The small stem that fits into the catch is liable to break. I snipped it off and replaced it with a 6-32 screw by drilling into the place where the stem should be and tapping it for a 6-32 screw. You can't see it in the pictures I have, which is unfortunate. Hopefully I can get the client who now owns this blaster to open it up and take a new set of internal pictures.
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Miscellaneous

Due to the subpar condition of the original shell I used, I had to add external overdraw protection as the stock mechanism was unreliable (due to some parts of the shell vital to it being taken out for other mods irrelevant to this one).
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This is a piece of 1/2" PVC which is secured by a 6-32 bolt to the rear scope, and slides along a 6-32 bolt in the cut down portion of the front scope. Drill holes and cut slots as necessary.

Again, I do not have final assembly pictures for some odd reason. I do have a section of firing video that I will edit in later, but I also lost the assembly video where I disassemble and reassemble the blaster showing how all the parts fit.

Here are random pictures that might help...
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Notes
  • The stock priming (and therefore catching) mechanism is retained.
  • The plunger rod is cut down from 12"+ to whatever length during final assembly and fitting. Ideally, the plunger rod is at a length such that the plunger head sits a small amount into the padding.
  • The spring length is cut after final plunger rod length is determined.
  • The maximum draw without extensive shell mods is around 5". Depending on how far forward you can get the plunger tube before the bushing and the plunger rod to extend, pullback will give you about 1" to 1.25" of space for solid length of the spring. Thus, fitting any spring that has CPI*wire diameter greater than .3 is going to be impossible without modifications to the spring via stretching unless you're willing to accept "rattle room" Between .25 and .3 will depend exactly on how the internals are built.
  • Given that the extended draw from 3.5" of stock to nearly 5" brings most springs to near-solid length, overdraw is a serious problem. Make sure to have a very solid shell and a very solid catch notch, as if you overprime the blaster with the spring at solid length, you are now directly applying a large amount of force to try and yank the catch plate out of the catch well.
  • You can opt out of sink drain and go with 1.5" OD plastic tube. McMaster sells nylon tube with 1/16" wall, which is slightly thinner than the ~1/8" wall of sink drain, if you really want to maximize your volume. However, this method will require a lot more work to a) anchor it to the shell B) attach a front bushing and c) secure your spring rest.

Edited by Zorn's Lemma, 27 January 2010 - 07:52 AM.

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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."
Kruger and Dunning (1999)

#3 JATDO

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Posted 26 January 2010 - 09:09 PM

This is amazing, I have been waiting for the write up for a while.
Just wondering, do you think you will ever sell these? How much would they cost?
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#4 Zorns Lemma

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Posted 26 January 2010 - 09:42 PM

This is amazing, I have been waiting for the write up for a while.
Just wondering, do you think you will ever sell these? How much would they cost?


Given that this was built for someone else, obviously I would sell one. However, given that I have to work in the confines of a shell, and that BBB shells differ a lot between generation, every product has to be a one-off and thus takes me a lot of time. PM me if you're actually interested.

Now, a couple of notes to add based on what people in IRC have commented upon.
  • The stock priming (and therefore catching) mechanism is retained.
  • The plunger rod is cut down from 12"+ to whatever length during final assembly and fitting. Ideally, the plunger rod is at a length such that the plunger head sits a small amount into the padding.
  • The spring length is cut after final plunger rod length is determined.
  • The maximum draw without extensive shell mods is around 5". Depending on how far forward you can get the plunger tube before the bushing and the plunger rod to extend, pullback will give you about 1" to 1.25" of space for solid length of the spring. Thus, fitting any spring that has CPI*wire diameter greater than .3 is going to be impossible without modifications to the spring via stretching unless you're willing to accept "rattle room" Between .25 and .3 will depend exactly on how the internals are built.
  • Given that the extended draw from 3.5" of stock to nearly 5" brings most springs to near-solid length, overdraw is a serious problem. Make sure to have a very solid shell and a very solid catch notch, as if you overprime the blaster with the spring at solid length, you are now directly applying a large amount of force to try and yank the catch plate out of the catch well.
  • You can opt out of sink drain and go with 1.5" OD plastic tube. McMaster sells nylon tube with 1/16" wall, which is slightly thinner than the ~1/8" wall of sink drain, if you really want to maximize your volume. However, this method will require a lot more work to a) anchor it to the shell b) attach a front bushing and c) secure your spring rest.

Edited by Zorn's Lemma, 26 January 2010 - 09:44 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."
Kruger and Dunning (1999)

#5 catmods

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Posted 27 January 2010 - 12:07 AM

What are the ranges? If they are high enough, I will be doing this to Giygas.
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#6 Zorns Lemma

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Posted 27 January 2010 - 12:36 AM

What are the ranges? If they are high enough, I will be doing this to Giygas.


Far. I mean, this close to doubles the existing plunger volume. Use your brain.
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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."
Kruger and Dunning (1999)

#7 Ryan201821

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Posted 27 January 2010 - 03:40 AM

This thing was being worked on for at least four, 8+ hour sessions of modding. Turned out pretty nice, and shoots very hard. Nice work.
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#8 Zorns Lemma

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Posted 27 January 2010 - 04:52 AM

What are the ranges? If they are high enough, I will be doing this to Giygas.




Punching a fairly large hole through cardboard at 15'. Those other holes were made by a PAS, 3k, and +bow.
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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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#9 mystefansdontflystraight

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Posted 27 January 2010 - 07:29 AM

I'm really impressed, I LOVE IT. I hope it arrives today.
I am gonna slap a bitchin PJ on this. I don't think that I have any guns that punch through cardboard at 5ft, let alone 15.
For the record, Zorn is a great person to do a contract with. His pricing seems reasonable (I traded for this, so I may not be the best judge) and as you can see from the photos, his work with homemades is top notch. I am honestly speecheless to see how much work went into it. More than was let on in PMs.

Edited by mystefansdontflystraight, 27 January 2010 - 07:33 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 meatballica

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Posted 27 January 2010 - 11:40 AM

How air tight is the plugner tube to plunger head? Can you stop the plunger head from going forward if you block off the coupler with your hand if your strong enough?
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#11 Zorns Lemma

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Posted 27 January 2010 - 11:51 AM

How air tight is the plugner tube to plunger head? Can you stop the plunger head from going forward if you block off the coupler with your hand if your strong enough?


Air leaks a little from around the bushing and the bolt run through it. However, the plunger head to plunger tube seal is about as perfect as you can get as the rubber washer is 1.5" OD and the tube is around 1.25" ID. If you seal off the coupler you will noticeably slow down the plunger rod though.
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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."
Kruger and Dunning (1999)

#12 meatballica

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Posted 27 January 2010 - 12:15 PM

How air tight is the plugner tube to plunger head? Can you stop the plunger head from going forward if you block off the coupler with your hand if your strong enough?


Air leaks a little from around the bushing and the bolt run through it. However, the plunger head to plunger tube seal is about as perfect as you can get as the rubber washer is 1.5" OD and the tube is around 1.25" ID. If you seal off the coupler you will noticeably slow down the plunger rod though.


But from the looks of the gun I am guessing that it gets way better air seal now since it has a better plunger head. Is there anything you plan on changing to it in the future? It seems worth doing seeing how it improves the guns functionality in alot of ways.
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"You've waged your war on nerves, but you can't crush the kingdom."

#13 Zorns Lemma

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Posted 27 January 2010 - 12:21 PM

How air tight is the plugner tube to plunger head? Can you stop the plunger head from going forward if you block off the coupler with your hand if your strong enough?


Air leaks a little from around the bushing and the bolt run through it. However, the plunger head to plunger tube seal is about as perfect as you can get as the rubber washer is 1.5" OD and the tube is around 1.25" ID. If you seal off the coupler you will noticeably slow down the plunger rod though.


But from the looks of the gun I am guessing that it gets way better air seal now since it has a better plunger head. Is there anything you plan on changing to it in the future? It seems worth doing seeing how it improves the guns functionality in alot of ways.


1) You can probably keep the stock plunger rod and just combine one of the plunger head replacement methods (mine or rork's) with some sort of spacer to get that extra length needed.
2) You can probably ditch the set screws and just go with solvent-weld.

This greatly cuts down on the machining needed making this mod much more accessible. There's not much else that can be done in terms of power optimization apart from extensive shell mods to allow for further draw. However, I experimented with it here: http://nerfhaven.com/forums/index.php?showtopic=17327 however come war day, the end product ended being unreliable. One issue was that I didn't let the epoxy used cure nearly long enough, but a larger issue was overdraw and stability. Perhaps an external pipe like I did here would allow for a extreme full-draw BBB, but I don't really have the time to do a lot of unpaid R/D...
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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."
Kruger and Dunning (1999)

#14 meatballica

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Posted 27 January 2010 - 12:37 PM

How air tight is the plugner tube to plunger head? Can you stop the plunger head from going forward if you block off the coupler with your hand if your strong enough?


Air leaks a little from around the bushing and the bolt run through it. However, the plunger head to plunger tube seal is about as perfect as you can get as the rubber washer is 1.5" OD and the tube is around 1.25" ID. If you seal off the coupler you will noticeably slow down the plunger rod though.


But from the looks of the gun I am guessing that it gets way better air seal now since it has a better plunger head. Is there anything you plan on changing to it in the future? It seems worth doing seeing how it improves the guns functionality in alot of ways.


1) You can probably keep the stock plunger rod and just combine one of the plunger head replacement methods (mine or rork's) with some sort of spacer to get that extra length needed.
2) You can probably ditch the set screws and just go with solvent-weld.

This greatly cuts down on the machining needed making this mod much more accessible. There's not much else that can be done in terms of power optimization apart from extensive shell mods to allow for further draw. However, I experimented with it here: <a href="http://nerfhaven.com/forums/index.php?showtopic=17327" target="_blank">http://nerfhaven.com/forums/index.php?showtopic=17327</a> however come war day, the end product ended being unreliable. One issue was that I didn't let the epoxy used cure nearly long enough, but a larger issue was overdraw and stability. Perhaps an external pipe like I did here would allow for a extreme full-draw BBB, but I don't really have the time to do a lot of unpaid R/D...


I understand. From the looks of this gun it looks really sturdy. Looks like it can hold its own iin a war.
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#15 Blacksunshine

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Posted 27 January 2010 - 10:09 PM

Wow Amazing work! Added this baby to the directory. Somewhere between mod and homemade.
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#16 archangel24

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Posted 14 April 2010 - 08:18 PM

What kind of ranges are you getting with this replacement?
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QUOTE(Talio @ Oct 14 2010, 10:37 PM) View Post

I would much perfer a game that's free of KY. I like it rough. Right, Vacc?

"She went all Ghetto Fab on you."


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