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Cobra Pistol crossbow modding


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Old 11-02-2015, 12:57 PM   #11
allu
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First shots fired!!!

Made two arrows out of 8 mm aluminium pipe I had. Conveniently a 6 mm bolt could be screwed into them so making a simple field tip was no problem. Picture of the shorter arrow (20 cm ~8 inches):

Cobra Pistol crossbow modding - Slingshot Crossbows

Tried them out first with the original cobra pistol crossbow and nope, not enough power for those. They flew alright up to 30 meters, but after that they quickly dropped down. Ended up losing the arrow when trying to shoot at 35 meters, I guess it buried itself into ground. To increase the chance of finding the arrows the next arrow was 25 cm long and about the longest the crossbow can handle. They flew even worse at range due to even more weight.

Encourage by the lack of power on the commercial one wanted to try out my design. Quickly wrapped the bow in place (going to do it better later on). Cocking it by hand turned out to be way easier than I thought it would be, honestly there's no need for cocking mechanism but it's definitely more convenient for one's fingers! The first time cocking it had to be really careful as I had no idea how the trigger would behave. It worked well apart from misfiring twice after I didn't cock it all the way. Was dying to give it a shot and man a few extra centimeters of draw length make a big difference! It shot very well and even all the way from 35 meters the bolts didn't drop short not once. Up close the velocity difference didn't seem that big but at range it definitely helps you squeeze some extra distance. I'd estimate the maximum distance at which you can still hit something is around 40 meters, but no room to test that far at my yard. Besides, accuracy suffers and I don't want to put too many dents on my house's wall, so going to stay at 30 meters maximum Didn't have proper plywood to waste for penetration tests, but an old rotten piece (9 mm thick) was snapped in half by the force of the arrow (the longer one)!

Cobra Pistol crossbow modding - Slingshot Crossbows

The trigger still needs some work. It works very well as it is, but the rubber bands could be changed to coil springs because it seems the rubber doesn't provide enough pull when it cools down. Got the string on my fingers once and not wanting to experience that again! Maybe some sort of safety for the lever could work, because it's honestly pretty scary to take your fingers off the string and hope for the best!

The cocking mechanism is the next step, hopefully my design will work and provide at least some leverage and therefore advantage. Some pics of the current state of the weapon:

Cobra Pistol crossbow modding - Slingshot Crossbows

Cobra Pistol crossbow modding - Slingshot Crossbows

That's all for today. Thanks for reading

-allu


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Old 11-02-2015, 04:08 PM   #12
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Quote:
Originally Posted by allu View Post
First shots fired!!!

Made two arrows out of 8 mm aluminium pipe I had. Conveniently a 6 mm bolt could be screwed into them so making a simple field tip was no problem. Picture of the shorter arrow (20 cm ~8 inches):

Cobra Pistol crossbow modding - Slingshot Crossbows

Tried them out first with the original cobra pistol crossbow and nope, not enough power for those. They flew alright up to 30 meters, but after that they quickly dropped down. Ended up losing the arrow when trying to shoot at 35 meters, I guess it buried itself into ground. To increase the chance of finding the arrows the next arrow was 25 cm long and about the longest the crossbow can handle. They flew even worse at range due to even more weight.

Encourage by the lack of power on the commercial one wanted to try out my design. Quickly wrapped the bow in place (going to do it better later on). Cocking it by hand turned out to be way easier than I thought it would be, honestly there's no need for cocking mechanism but it's definitely more convenient for one's fingers! The first time cocking it had to be really careful as I had no idea how the trigger would behave. It worked well apart from misfiring twice after I didn't cock it all the way. Was dying to give it a shot and man a few extra centimeters of draw length make a big difference! It shot very well and even all the way from 35 meters the bolts didn't drop short not once. Up close the velocity difference didn't seem that big but at range it definitely helps you squeeze some extra distance. I'd estimate the maximum distance at which you can still hit something is around 40 meters, but no room to test that far at my yard. Besides, accuracy suffers and I don't want to put too many dents on my house's wall, so going to stay at 30 meters maximum Didn't have proper plywood to waste for penetration tests, but an old rotten piece (9 mm thick) was snapped in half by the force of the arrow (the longer one)!

Cobra Pistol crossbow modding - Slingshot Crossbows

The trigger still needs some work. It works very well as it is, but the rubber bands could be changed to coil springs because it seems the rubber doesn't provide enough pull when it cools down. Got the string on my fingers once and not wanting to experience that again! Maybe some sort of safety for the lever could work, because it's honestly pretty scary to take your fingers off the string and hope for the best!

The cocking mechanism is the next step, hopefully my design will work and provide at least some leverage and therefore advantage. Some pics of the current state of the weapon:

Cobra Pistol crossbow modding - Slingshot Crossbows

Cobra Pistol crossbow modding - Slingshot Crossbows

That's all for today. Thanks for reading

-allu
Looks good so far


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Old 11-04-2015, 06:33 AM   #13
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Great build Allu! I was looking forward to what it was going to look like in the end. Also, thanks for your idea on screwing bolts in the aluminum shaft. Up til now I've been very painfully inserting commercial arrow bullets in the shaft. Now all I have to do is screw it a bolt or glue it in if needed and sharpen the tip with an angle grinder. Why didn't I think of it before??
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Old 11-04-2015, 08:18 AM   #14
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@ slingshot_lover: Thanks!

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Great build Allu! I was looking forward to what it was going to look like in the end. Also, thanks for your idea on screwing bolts in the aluminum shaft. Up til now I've been very painfully inserting commercial arrow bullets in the shaft. Now all I have to do is screw it a bolt or glue it in if needed and sharpen the tip with an angle grinder. Why didn't I think of it before??
Yeah it's a really simple way, was surprised how well they actually fit in there. Also if you want to make a broadhead you can make one simply by adding a wing nut. Leave 1-2 cm of the bolt extending from the tube, screw the wingnut tightly in place and sharpen the bolt and the "wings" of the wing nut. Simple broadhead done in no time! Will try it out myself once I get my hands onto some M6 wingnuts, currently I only have M8 ones.
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Old 11-04-2015, 08:33 AM   #15
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Excellent idea! I never would have thought of that! Like I mentioned before, most stores here are like you walk up to the store and there's a guy there and you have to ask him specifically want you want and he'll go get it. You can't browse inside! Other shops are just too messy to find anything. And mall hardware stores don't have all you need. I like to look around for myself to get inspiration. I'll try to get pictures if I can haha.

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Old 12-02-2015, 03:01 PM   #16
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Dealing with personal issues and looking for job has taken its toll, so my time or interest for this project has been kinda of gone. Feeling better now and accepting my fate as unemployed for now made some time for crafting.

Well here's where we got at first:

Cobra Pistol crossbow modding - Slingshot Crossbows

Just a simple cheek rest and arrow rest besides little fine tuning here and there. Also cut of the excess material on bolts and this is how it looks like on top:

Cobra Pistol crossbow modding - Slingshot Crossbows

Then we get to the reload mechanism. Well where should I start from... It makes the weapon look pretty weird to be honest and unfortunately is full of issues. Didn't finish it yet, but not sure if I will even. First off here are the pics:

Cobra Pistol crossbow modding - Slingshot Crossbows

Cobra Pistol crossbow modding - Slingshot Crossbows

So the good things first:
-It does make cocking it easier, at least with low poundage (tested with rubber).

And the downsides:
-Ruins the ergonomics, very little space around the pistol grip and the arms pulling the string lessen that space even further.
-Major difficulties having the loading arms staying apart from each other instead of being squashed against the body. Properly made metal arms would help with this, but still unsure if it would help all that much.
-I thought it could be used by pressing the stock against the ground and using your body mass to pull down the string. Sure it works, the lever just hits the ground before the weapon is spanned, forcing you to tilt the weapon forward.
-Looks pretty weird.

So I'm pretty unsure if I should put time and effort into trying to fix something that may never work or just leave it be as it is now, without the whole cocking mechanism thing. It would make it pretty useless though, because cocking it without any sort of aid is painful and I could just go back and use the original Cobra pistol crossbow body. Another design that worked in theory but not in practice, I guess this happens when building stuff!

-allu
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Old 12-02-2015, 04:31 PM   #17
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Hmm, yes, looks a bit awkward. A cocking mechanism is nice to have but not so easy to implement. What about a wippe style lever, stored underneath but swinging around the front end?
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Old 12-02-2015, 06:00 PM   #18
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Quote:
Originally Posted by RalphG View Post
Hmm, yes, looks a bit awkward. A cocking mechanism is nice to have but not so easy to implement. What about a wippe style lever, stored underneath but swinging around the front end?
Honestly I think I'll just finish this design without any sort of cocking aid. It's just too much of an hassle to implement a new design into something designed for a completely different mechanism. Well I learned about working with aluminium, nice material and will definitely use it more one day. On my next build I'll just go medieval, maybe I can finally actually finish the build and have it working as intended.

-allu
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Old 12-03-2015, 10:11 AM   #19
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Would you be interested in selling the original cobra without the spring?
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Old 12-03-2015, 11:38 AM   #20
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Would you be interested in selling the original cobra without the spring?
Sure I could but honestly the postages would cost more than buying a new one from ebay/amazon/local store. Not sure where you're living at, but unless you're in Finland then there's no point in it, just go get a new one that's not scratched up and used like mine (Just sent a package to my gf living abroad and it cost 24 for less than 1 kg package so it'd be way over 30 for the whole cobra, which is rather heavy). So I have to say no, not wanting to waste your money


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