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Crossbow Plunger Head Replacement / Reinforcement


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#1 Soothsayer

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Posted 13 September 2009 - 04:28 PM

This write up is following my needs and my preference, you can/will need to alter the design to fit your crossbows specifications.


This write up will show you how to replace/repair your crossbow's plunger head. You will need the following:

Power drill with assorted drill bits
Two inch bolt (depending on your preference, the diameter of the bolt will vary, and a nut)
Polycarbonate or another strong material capable of keeping your springs compressed
Epoxy putty
dremel (or something to cut through a metal bolt)
rubber washer
a piece of leather


Step one:
Chop off the tip of your plunger rod
Posted Image

Step Two:
Drill a hole big enough to fit your bolt snugly down the center of the front of the plunger rod
Posted Image
Posted Image

Step Three:
Drill 4 (it's actually 8) holes through these spots on your plunger rod
Posted Image
This helps later on, trust me.

Step Four:
Take your 2 inch bolt, and dremel off head of the bolt, then take some pliers and twist it into the hole in the front of the plunger rod
Posted Image
Posted Image


Step Five:
Take your polycarbonate, and cut out 2 circles that fit losely in your plunger tube, making sure they're wider than your spring of choice's diameter.
Posted Image

Final Steps:
Take your epoxy putty and TIGHTLY pack it around the sides of your bolt, making sure the epoxy leaks into those 8 holes you drilled from before. I'm not going to recommend anything else than epoxy putty to do this, because of the constant (and extreme) pressure trying to push the bolt out.

Now, taken your poly. circles, rubber washer, and leather and put them on in this order. The leather provides cushioning.
Posted Image


There you go, you now have a very efficient set up. Like I said in the beginning, with how many different plunger tube sizes and lengths people vary, I can't really give everything the correct answers. I use the same plunger tubes in +bows, so I just used the rubber washers that fit those. I'm sure with some scissors you could make the rubber washer/fashion something to fit your plunger tube.

Any questions?

Edited by Soothsayer, 13 September 2009 - 06:54 PM.

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#2 Draconis

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Posted 13 September 2009 - 06:40 PM

Now, this is just me, but wouldn't it mate more sense to use a screwdriver to insert the screw in to the hole, and THEN cut of the end? Rather than using the wrong tool for the job? Also, if you are doing this, folks, I would suggest using an aluminum screw if it is #8 or larger. 1/4" or larger, nylon is your friend. The extra mass added to the plunger head will lower the acceleration, and thus performance.
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#3 Soothsayer

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Posted 13 September 2009 - 06:54 PM

Now, this is just me, but wouldn't it mate more sense to use a screwdriver to insert the screw in to the hole, and THEN cut of the end? Rather than using the wrong tool for the job? Also, if you are doing this, folks, I would suggest using an aluminum screw if it is #8 or larger. 1/4" or larger, nylon is your friend. The extra mass added to the plunger head will lower the acceleration, and thus performance.

How would you get the nuts on? the last picture shows that you use nuts to secure everything. If you do not remove the bolt head, it would disable you from putting nuts on disregard I read this wrong. Added mass? It barely makes the thing any heavier. If this much extra weight is going to hinder your crossbow, you need to reconsider your choice in springs.



I will say though, with my method of inserting the bolt, you insert the end that you cut /first/, so the clean end makes it easier for the nuts to be put on.

Edited by Soothsayer, 13 September 2009 - 07:01 PM.

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#4 Kid Flash

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Posted 13 September 2009 - 07:03 PM

Just out of curiosity, did you get 2 crossbows out of an ebay auction with broken plunger heads? I like how you did it sooth. As long as it works is what matters. So how many crossbows do you have now?
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#5 Soothsayer

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Posted 13 September 2009 - 07:07 PM

Just out of curiosity, did you get 2 crossbows out of an ebay auction with broken plunger heads? I like how you did it sooth. As long as it works is what matters. So how many crossbows do you have now?

No, these are pictures of frantoinette's plunger rod and plunger head. I have only 2 crossbows. I just got done with redoing one, I'm going to put pictures up some time this week, along with another write up that's gonna really change the way people look at integrations in crossbows.
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#6 Kid Flash

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Posted 15 September 2009 - 06:24 PM

Ah. Alrighty. Not too big of a fan on integrations but maybe I'll change with your writeup.
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#7 CA13

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Posted 15 September 2009 - 07:20 PM

Cool mod. Are the washers of polycarbonate too overkill? I thought they would add too much weight to the rod. You probably could just use a flat-head screw, with a foam disc and rubber washer (washer/bushing seals, while the foam disc softens the plunger movement).
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#8 Zorns Lemma

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Posted 16 September 2009 - 12:47 PM

Cool mod. Are the washers of polycarbonate too overkill? I thought they would add too much weight to the rod. You probably could just use a flat-head screw, with a foam disc and rubber washer (washer/bushing seals, while the foam disc softens the plunger movement).


Yea, solid washers behind the neoprene is complete overkill. It's not like they're needed to effectively compress the spring or anything.
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#9 Soothsayer

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Posted 16 September 2009 - 03:41 PM

I don't know what parallel universe you're all from, but if two polycarbonate disks are going to hinder your crossbow, I pity you greatly. Trust me, people have seen my crossbows in action, they shatter almost all other crossbows they meet in range, most of the time without the addition of bungees. Everything I'm doing is completely efficient. It's not a matter of opinion, it works, it's fact. Christ. Oh, and trust me, they're needed. Just a rubber washer? your springs will claw away at the washer, morph it, bend it, just, slowly destroy. It'll work for a /while/, but why not just add the 2 polycarbonate disks and have it last forever? Cause that would be smart. Huh, imagine that.
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#10 Coop

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Posted 16 September 2009 - 04:05 PM

I really don't think two little polycarbonate disks are going to lower ranges, lol. I don't know why you think it's overkill, CA13, considering many plunger head replacements use metal disks and they do just fine.

Edited by Coop, 17 September 2009 - 02:14 PM.

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On the other hand, the guy who posted before me used the word 'fuck' a lot so he probably knows what he's talking about.


#11 Zorns Lemma

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Posted 16 September 2009 - 04:40 PM

Just a rubber washer? your springs will claw away at the washer, morph it, bend it, just, slowly destroy. It'll work for a /while/


Both your sarcasm sniffer and common sense catcher seem to be loose a few wires. But maybe Mr. Master of Crossbows knows how to get a thin rubber disc to hold more than 3 lbs of force.
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#12 Soothsayer

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Posted 16 September 2009 - 05:32 PM

Just a rubber washer? your springs will claw away at the washer, morph it, bend it, just, slowly destroy. It'll work for a /while/


Both your sarcasm sniffer and common sense catcher seem to be loose a few wires. But maybe Mr. Master of Crossbows knows how to get a thin rubber disc to hold more than 3 lbs of force.

Using sarcasm on the internet is retarded in the first place. Speak with conviction or sit on your hands.
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#13 Draconis

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Posted 17 September 2009 - 10:52 AM

Speak with conviction or sit on your hands.


I believe you've already been convicted in the court of public opinion. I don't think "shatter" is the correct term for "meeting the established average" in terms of performance.
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#14 Soothsayer

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Posted 17 September 2009 - 10:18 PM

Speak with conviction or sit on your hands.


I believe you've already been convicted in the court of public opinion. I don't think "shatter" is the correct term for "meeting the established average" in terms of performance.

"...they shatter almost all other crossbows they meet in range..."

They've met quite a lot, just not groove or split.
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#15 BustaNinja

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Posted 17 September 2009 - 10:48 PM

Because we all know that range tests are all that matters...

This is Nerf, but a dick waving contest.

Could this applied to a 3b? it seems sound, but seriously man, do you really need to defend your plastic that much?
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#16 Soothsayer

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Posted 18 September 2009 - 12:16 AM

Because we all know that range tests are all that matters...

This is Nerf, but a dick waving contest.

Could this applied to a 3b? it seems sound, but seriously man, do you really need to defend your plastic that much?

It'd prolly be a lot easier for a BBB, I'm buying one of the new red ones this weekend to try it out. This'll sound egotistical maybe, or like, conceited, but honestly, I just want everyone to have the most efficient blasters as possible, and add a lot of life to their guns. One of the main, if not the /main/ reasons I'm into this hobby is the community. You can say I'm full of it or whatever, but I mean it, I just want to help out as many people as I can.
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#17 Ice Nine

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Posted 18 September 2009 - 12:37 AM

Could this applied to a 3b?


Not engaging on anything else.

Posted Image

Taken from this thread.

More akin to the original mod Soothsayer posted up for his Crossbow is Zorn's plunger tube replaced BBB, as seen here. I haven't seen or heard him talk or post about it recently so there may have been a problem with it but I also haven't seen him mention a problem with it; if there was you'd hear about it. The UChicago student body is pretty self-deprecating.
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#18 Soothsayer

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Posted 18 September 2009 - 01:21 AM

I've heard mixed results with that. If you do it correctly, and get name brand epoxy putty, and eliminated all dead space in the front of the BBB, it works very very well.
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#19 Zorns Lemma

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Posted 18 September 2009 - 12:47 PM

name brand epoxy putty

Using the aluminum standoff method and loctite epoxy + ace plumber epoxy putty, the plunger head has stood up to my Zorn Spring Combo (k19 + [k26]) well enough that the catch well deformed first.

It also shot on par with +bows and lasted 2 Chicago wards and 1.5 MN wars (catch well shat itself day 2 of the 2-day FAIL-MN war).

Also, the plunger tube replaced BBB shat itself within a few minutes of being assembled. I probably went overboard with the 6" of draw (the rear piece collapses on itself due to weird force transfer through the catch tabs on the side).

As to the OP's mod, I actually think it's a pretty good deal, if not a bit of a copy of what dizzy and rork already did. My only suggestion is that since you're using polycarb washers, you should mold them to form a bit of a dimple and thus help form the rubber washer into that cup shape that make for great seal.

Also, using the nut-on-screw method is a bit risky when you put in a lot of springs as there's a high chance of it shaking loose from the force when primed. impact when fired, and general vibrations. That's why the standoff is the superior method for BBB plunger heads as you have way more effective threads.

Having never opened an xbow, I have no idea if there's enough room for a standoff. Tapping a hole would probably work, but that gets real messy real fast.
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#20 atomatron

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Posted 18 September 2009 - 08:24 PM

Well here's my version (I had already started working on it when you posted your way)-
Posted Image

A 2" bolt put through the front part of the plunger rod (the head is visible) there is a nut in the epoxy putty.
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