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Discussion Starter · #1 ·
Seeing Joerg badassing the Cobra pistol crossbow was fun to to watch, but sadly enough the concept of a magazine was already implemented by pimpmycobra.com. Joerg says he has no other modifications to do and the Cobra has reached its limits to what can be done to it. I disagree - there's a modification which is unique and could go commercial: Make it shoot ball bearings. Ball bearing pistol crossbows already exist, they are "dual purpose" pistol crossbows which have a top guiding rail with magnet to guide the bearing/bolt out. (example of such a bow: http://outdoorhobbies.co.uk/raptor-1377-p.asp) but no one has modded an existing crossbow to shoot ball bearings AFAIK. Adding a "hex-nut shooter"-type magazine would be the cherry on the pie.
 

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Sadly, the mod is two hundred bucks.... Silly for a $30 crossbow.
 

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I did mention the pimpmycobra product in the original video. My mod has several differences. The main difference is that these guys use fance magazine springs to push down the bolts. These springs are expensive, bulky, and awkward to handle.

My advantages:

- Much less bulky
- Easier to load
- Front Weaver rail
- Inexpensive

If I make a product out of this, 19,90 is my target price for the kit, plus maybe another 9,90 for those who want the front handle.

Why not shooting ball bearings? Because it is not powerful enough. 160 fps for a 10mm steel ball means under 5 Joules... less than an air pistol. The advantage of the Cobra is that it can shoot bolts, that have a lot more penetration power.

Bolt shooting Cobra = Serious weapon
BB shooting Cobra = Toy
 

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Discussion Starter · #4 ·
I did mention the pimpmycobra product in the original video. My mod has several differences. The main difference is that these guys use fance magazine springs to push down the bolts. These springs are expensive, bulky, and awkward to handle.

My advantages:

- Much less bulky
- Easier to load
- Front Weaver rail
- Inexpensive

If I make a product out of this, 19,90 is my target price for the kit, plus maybe another 9,90 for those who want the front handle.
You are very right that your implementation of the mod is far superior. And what they are asking for their pimped cobra is criminally high, even if it's all aluminium. I meant that the concept itself was not new, your changes to it are however. I just built an entire pistol crossbow with your magazine (for three bolts, I wanted it to support 5 but liked the streamlined design of a low magazine) and it works perfectly.
2014-05-21 23.50.46.jpg
Why not shooting ball bearings? Because it is not powerful enough. 160 fps for a 10mm steel ball means under 5 Joules... less than an air pistol. The advantage of the Cobra is that it can shoot bolts, that have a lot more penetration power.

Bolt shooting Cobra = Serious weapon
BB shooting Cobra = Toy
You are right in that the power of the weapon goes down and so goes its usability as a serious weapon, but isn't it so that the ball bearing, having less weight, would achieve higher FPS? I saw data on one of those dual purpose crossbows and it says:
Code:
Velocity : 32 Grain 8mm Balls :  410 ft/sec
Velocity : 30 Cal Lead Projectiles 308 ft/sec
Velocity : 361 grain 17" Bolts : 200 ft/sec
Power : 32 Grain 8mm Balls 12ft/lbs
Power : 30 Cal Lead Projectiles 23.3ft/lb
Power : 361 grain 17" Bolts 18ft/lbsWeight : 5.1kg
Still, penetration I presume would be horrible even on the lead projectiles which are supposedly more powerful in terms of energy than the bolts.
 

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thinks TBG smells better than roses
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@MTS--That pistol crossbow you built is cool.
Do you have a post for showing it off? I'd like to see more of it.
 

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I agree with Mike, that crossbow is pretty cool. I'd like to see how you did that and hear how you think yours compares to a mass produced model like the cobra. I've tried making several crossbow like that of my own design but I never like the way they turn out, mostly because my trigger mechanisms are less than perfect. I'd love to see how you made yours.
 

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Im from Holland, isnt that weird?
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I like the idea! But i'm not sure how the bow would hold up shooting those bearings. It might be like dry firing and if you do that a lot you might break the bow (i broke mine that way, i was young and foolish at the time ;) ) good luck with you project!
 

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Discussion Starter · #10 ·
Well, the bolts the thing shoots at 160 fps aren't much heavier than a 10mm steel ball... so the speed won't likely be higher, right?
I doubt it. I don't have a scale handy but you can feel the bolt is much heavier. Granted, I only own aluminum bolts. I'll get the weight stats of aluminium and plastic bolts up today as I know someone with a digital scale and plastic bolts.

@MTS--That pistol crossbow you built is cool.
Do you have a post for showing it off? I'd like to see more of it.
No, but I will make one. These are really easy to build as well, the bow is made from fiberglass tent poles (actually, child bicycle flags from http://www.action.de/ at 2,70 Euros). My "production company" will release a video series I hope will go viral about improvised weapons soon. It's a comedic series laden with special effects and blue screen tech and I'm saving the best, like a How-To on my "The Intimidator" electro-pneumatic 20mm rifle ( intimi.jpg ) for this series.

I recently painted the crossbow too, looks a lot more fierce: finished.jpg

I agree with Mike, that crossbow is pretty cool. I'd like to see how you did that and hear how you think yours compares to a mass produced model like the cobra. I've tried making several crossbow like that of my own design but I never like the way they turn out, mostly because my trigger mechanisms are less than perfect. I'd love to see how you made yours.
Thanks! It's extremely reliable, shooting a bolt every time you cock it. The power was too high initially, I added theraband red to the back of the bow to "increase its power" (the theraband, resting on a wooden pedestal in the middle, pulls the bow forward, when you cock you pull the bow backward, the strength of the combined rods/theraband is synergetic) but I estimate the pull was over 100 lbs and the cocking rods were completely unusable at these power levels (unless you are a gorilla), so I cocked the string manually once, shot, and stuff broke down due to the force. SO now I just use two fiberglass rods and it cocks easily, in comparison with my 50 lbs commercial pistol crossbow it's a bit weaker but comparable. The commercial one will penetrate two sides of a soup can from point blank range stopping at the fletching in the second hole, this home made one will penetrate only one side and puncture a tiny hole in the other side stopping at the fletching at the first hole.

The biggest problem is the tendency of the string to jump the ball. When that happens you truly dry fire the weapon and then something WILL break.
Well, my original post mentions 8mm steel balls for this reason. They seem to fit in a crossbow's slot perfectly, aligning the string just at about the right height. Lets assume an 8mm steel ball weighs less than even a plastic bolt and does get the 400+ fps as some manufacturers of bearing-shooting crossbows claim. As the world's expert on slingshots (according to me), I don't have to explain to you that this would outperform the majority of slingshots with ease. However, it *is* like dry-firing. But on the other hand, my commercial pistol crossbow dry fires on 20% of the shots because the string jumps the bolt and it survives to this day. I built a pump-action magazine-based marble shooter two weeks ago and the para-cord string takes away the marble, which is 16mm in diameter, every time. But in all fairness, I did use three pieces of para-cord with a small amount of duct-tape wrapped around the center. I will add a guiding rail to one of my crossbows and try bearing shooting out. Too bad I don't have a chrony to test the results, but I will use the inflicted damage as a comparison method instead.
 

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Discussion Starter · #11 ·
Alright the results are in;

Code:
9.5mm steel ball - 3 grams
16mm marble - 6 grams
6.5" Plastic bolt - 6 grams
6.5" Aluminum bolt - 10 grams
The scale has a one-gram precision but it is clear the bolts have more weight.
 

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You are very right that your implementation of the mod is far superior. And what they are asking for their pimped cobra is criminally high, even if it's all aluminium. I meant that the concept itself was not new, your changes to it are however. I just built an entire pistol crossbow with your magazine (for three bolts, I wanted it to support 5 but liked the streamlined design of a low magazine) and it works perfectly.
View attachment 11611


You are right in that the power of the weapon goes down and so goes its usability as a serious weapon, but isn't it so that the ball bearing, having less weight, would achieve higher FPS? I saw data on one of those dual purpose crossbows and it says:
Code:
Velocity : 32 Grain 8mm Balls :  410 ft/sec
Velocity : 30 Cal Lead Projectiles 308 ft/sec
Velocity : 361 grain 17" Bolts : 200 ft/sec
Power : 32 Grain 8mm Balls 12ft/lbs
Power : 30 Cal Lead Projectiles 23.3ft/lb
Power : 361 grain 17" Bolts 18ft/lbsWeight : 5.1kg
Still, penetration I presume would be horrible even on the lead projectiles which are supposedly more powerful in terms of energy than the bolts.
Could I pay you to make a magazine kit for a cobra rifle and ship it? I'm in California.
 
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