Cobra Pistol crossbow modding

Discussion in 'Slingshot Crossbows' started by allu, Oct 16, 2015.

  1. allu

    allu Junior Member

    133
    0
    0
    Hi there!

    For a long time I've been planning on getting a cobra pistol crossbow, but never got it done until now. I'd have bought two straight for the extra prod and string, but unfortunately they weren't half price anymore, just -25% :( So had to go with one and see what can be done with it.

    It came dark before I had a chance to take too many test shots with it, but so far it seems good for now. Performance is decent, but I have to say the trigger is pretty bad. The trigger pull is not too heavy, but being a pistol it easily throws off your aim. Also the safety will be the first thing to break, it wobbles already out of the box and feels really badly designed overall. Getting the string off was a pain at first, but using a rope to simply pull back the ends of the prod allowed stringing it relatively easily. Original iron sights weren't too great, but were surprisingly zeroed in pretty well out of the box. Though I replaced them with a red dot sight I had lying around and added a rail and flashlight. I was impressed by the built quality, honestly the aluminium parts felt great. However the plastic parts were a bit squeky. The included bolts and the ones I bought are way too light, I thought they'd be a lot heavier than what they are. They are hollow though, so gotta see if something could be fitted inside them :p Overall a nice little toy for it's price.

    What I'm planning to do is to improve it with the original body and eventually build my own version of it. It definitely needs a stock because I simply hate aiming with stockless weapons, my hands are too wobbly for them. Also something needs to be done for those bolts, they're just too light weight. Something else that needs to be changed will come up at some point for sure, but can't list anything else right now.

    -allu
     

    Attached Files:

    Last edited: Oct 16, 2015
  2. slingshot_lover

    slingshot_lover New Member

    479
    0
    0
    Looks good so far :D Please do a shooting Video :)
     

  3. allu

    allu Junior Member

    133
    0
    0
    Finally got some proper shooting done. At 10 meters it seemed really good and all the way up to 20 meters the performance was good enough, but after 20 meters the struggle starts. At 30 meters hitting the target gets difficult as bolts drop a lot before hitting it and some bolts just nosedive and hit the ground near the target, never to be found again. it's a close range weapon, but had to try it at range :p Not exactly impressed with it, I expected a little bit more power but the lightweight bolts slow down fast.

    Not too much can be done with the crossbow itself to increase it's performance so I've been designing a model with 2-3 cm extra draw length. Do you think the prod could handle a little bit of extra stretching as it doesn't exactly look all that maxed at it's current state. That extra draw would give a nice boost in performance for sure!

    Also the bolts are pretty cheap trash, maybe a few bolts from a dozen fly well, half of them fly with a bit unexpected path and a few just nosedive or otherwise fly incorrectly. I started with 27 bolts and ended with 17, mostly due to long range shooting. Those little bolts disappear damn well into the ground :/

    -allu
     
  4. allu

    allu Junior Member

    133
    0
    0
    Trying to make bolts heavier failed miserably. Took one of those completely hollow arrows, jammed some bolts (with the head cut off) and secured them with glue. Well the glue didn't hold and they started pushing the arrow tip off of the shaft, but before that the whole shaft bend. Like probably 20-30 degrees. Well I guess it was too heavy after that, probably over twice as heavy as a normal bolt and flew already quite slow, so impact force seemed to have decreased instead of increased. I guess the short power stroke and relatively low poundage can't launch much heavier arrows at decent speed.

    So I decided to start building my version of this crossbow. Well it's not really a pistol anymore, but so far I only have a few parts of the trigger ready. This time I decided to start from the trigger and build the stock around it. Of course I have plans for the stock too, but with limited tools the diameters of the parts always varies a little bit making the trigger always the trickiest part. And the trigger in the commercial product was pretty bad, so I wanted to try if mine could have a better one! Most likely not, but at least I tried :D Hopefully tomorrow I have more time for this, today I wasted half of my day off for some bureaucratic crap, gotta hate being unemployed... :rolleyes: A few pics of the trigger system so far (the actual trigger piece is still to be done and the piece holding the string will be centered and polished more):

    [​IMG]

    [​IMG]

    There already are tons of shooting videos of the cobra pistol crossbow on Youtube, but if my design shoots well I may consider uploading a video. But just consider, not promising anything yet. But first I gotta build it! :D

    -allu
     
    Last edited: Oct 19, 2015
  5. allu

    allu Junior Member

    133
    0
    0
    Have been busy lately but finally tonight I had some time for crafting. Got to a good pace and a lot of progress happened. Without further introductions this is how it looks like now:

    [​IMG]

    So got some parts cut out a plywood. First concentrated on building the front section of the gun and the trigger to make sure everything is working just fine. A pro tip: if you ever wonder what kind of trigger design to go with when you have only limited tools available go with the simplest one. Man it takes eternity to fine tune this kind of trigger (which is still very simple), first it's impossible to make the trigger nut turn into the loaded position and after adjustments it doesn't want to release it anymore. Spend a good few hours filing and adjusting the position of those parts but finally it's starting to feel good. A picture of how it behaves with some pressure on it:

    [​IMG]

    It still takes some effort to make the trigger nut turn into a loaded position with a string (just to simulate spanning it with actual bow on it), but with a bit more polishing it should be good to go. Now it stays cocked even if the spring fails, so no chance of misfires on that part. I tried to make the trigger sensitive and the stroke short but I think I kinda overdid it :D Pulling the trigger just a few millimeters is more than enough to make it go off and it doesn't really have a feel on it. Though might be just a matter of getting used to it, at least it's not heavy to pull. That's what I was looking for with it anyway, so I guess I succeeded :p Glad I got it working eventually, it was getting frustrating when it still wasn't working after an hour but at least now I can use it as a sling x-bow if the cobra pistol crossbow prod doesn't work well with it. It's pretty noisy though because the "rolling nut" hits the pipe in front of it that prevents it from spinning around, but a little bit of rubber or some other soft cushioning should fix the problem.

    It's still missing lots of parts, so this is no way the finished product. It still needs the cocking lever, some flat steel parts and the stock piece needs some plywood pieces around it to keep it in place. And a scope mount, arrow holder etc etc, so a lot needs to be done still. But this is all for tonight.

    -allu
     
    Last edited: Oct 23, 2015
  6. allu

    allu Junior Member

    133
    0
    0
    Of course the whole body ended up being a complete failure. The loading mechanism just doesn't work well with it. The body is way too wide and too many bolt heads sticking out of it. This is how the spanning mechanism was supposed to work:

    [​IMG]

    And spanning would happen like this:

    [​IMG]

    Tried it out with some rubber and it does offer some leverage over stretching the rubber by hand, or then it just feels lighter because it's more comfortable. No idea, maybe it works or not can't really tell. Oh well, it seems it's time to go back to the drawing board and try to keep the body width down (max 2-3 cm), because the hooks pulling the string back can't be too far apart. Damn it, I thought it could be made that way but apparently not. Wasted time and resources to a useless failure, I guess this is what crafting is all about! Can't always win but never give up... :rolleyes:

    -allu
     
  7. allu

    allu Junior Member

    133
    0
    0
    While looking for flat steel in the local hardware store I came across some really nice aluminium parts. Had to buy 40 x 3 mm and 25 x 3 mm flat aluminium bars and an 8 mm aluminium tube. Finally I can make arrows at least :D

    I have always tried to make things too complicated for what can be done with the tools and materials I have available, so this time I went as simple as possible. After 4 hours of crafting it looks like this:

    [​IMG]

    Simplicity at its best, the whole trigger mechanism is attached to the main body, so basically all the other parts could be taken out of it and it could still fire. Although it sounds simple the trigger turned out to require a lot more work than I could have ever imagined. The flat steel I have is sold as 2 mm thick, but in reality it's slightly over 3 mm. On the other hand the aluminium bars are slightly less than 3 mm thick. So fitting the trigger parts that are made out of flat steel between those outer panels requires a lot of filing and sanding, because the gap is slightly less than 3 mm and there's no way to change that. Spend two hours on that and still one part doesn't fit well. Sigh, if I just had a fancy tool that could do that in five minutes. Angle grinder would take too much material off and weaken the build, and on the other hand a hand file is so damn slow. But still gotta go with the latter one, this build is really getting on my nerves :rolleyes:

    There's something positive too. It's nicely compact and light weight thanks to aluminium parts, and it only requires a few more parts before it's fully operational. Re-designed the cocking mechanism shown in the earlier post and it should work just fine with this build, the body is only 9 mm thick with bolt heads adding extra few millimeters. Trying my best to work on this tomorrow, we'll see how this is gonna end up... :rolleyes:

    -allu
     
  8. Petebacardi

    Petebacardi New Member

    127
    0
    0
    Hey Allu!

    Nice job so far! Don't give up! The first build is always the most frustrating but once you get the hang of it, it should all fall into place easily.

    I also thought and tried all sorts of complicated systems but being limited in tools really stops you from progressing further. Sometimes sticking to the old fashion methods work the best ;)

    What power tools do you have so far? I managed quite well with a power saw, jigsaw, power drill, power sander and angle grinder.

    I found that working with wood work out pretty well for me for making sling rifles/guns since its easier than working and shaping metal.

    I haven't tried those tiny bolts for the crossbow pistols yet and I doubt I can find them in shops here neither but from what you say and from what I heard, they get lost easily and don't have that much power. Was more satisfied with commercial fiberglass arrows and homemade aluminum bolt, had more "oomph" if you know what mean!

    Hang in there and keep going!
    Cheers
     
  9. allu

    allu Junior Member

    133
    0
    0
    Thanks for the post! :)

    It's not exactly my first build, but definitely the first more advanced one :D

    I have the same tools to use as you have apart from the power saw because the blade snapped last year and still haven't found a replacement one as it's probably 15 years old. Power sander is missing too but instead I have some sanding rolls (or whatever they're called, basically just a wheel attached to a drill bit and a sanding paper around it) for the power drill. Have managed so far, but some extra tools would be nice to have and would also speed up building a lot.


    Aluminium is actually really nice material to work with on small builds (too pricey for big builds though). Steel is just too hard to work with with the tools I have and that's why I stay away from it unless it's necessary to use like in a trigger for example. But wood and especially plywood are still far easier to work with than any metal.

    Yeah those tiny bastards definitely get lost without leaving a trace! Have lost over 10 of them after having shot about 100 shots and just can't get my head around where did they go. There must be some black magic going on in here :rolleyes: That's why I got that 8 mm aluminium tube that will make nice arrows with proper arrow heads. Still need to get those, the homemade ones always fail sooner or later, let alone how impossible it is to make them identical. No idea how long and heavy the arrows should be, but luckily testing stuff is always fun :D

    And back to the build. Spend a good while working on it and here's the result:

    [​IMG]

    So much more comfortable to hold with an actual handle instead of just that flat bar. The main body is starting to be almost ready, still needs a few parts but it's functional as of now. Although the damn trigger still wants to get stuck if all the bolts are tightened all the way. The nut rolls freely, but the lever connecting the trigger and the nut still wants to stop co-operating every now and then, so more filing in sight, sigh. Besides that it works great and the trigger pull is really light, way lighter than what it was before. Haven't tested how well it holds with a heavy load yet, but with theraband blue tubes it holds no problem:

    [​IMG]

    That's all for tonight, thanks for reading! :)

    -allu
     
  10. allu

    allu Junior Member

    133
    0
    0
    Okay let's say that I'll never ever try building a trigger inside such a narrow body. 3 mm is not a whole lot and that ended up being exactly the reason why the trigger jammed as soon as you tightened the screws. I thought it was the linkage arm between the trigger and the trigger nut, but nope it was the return spring. Didn't even realize to think about how compression springs widen as they are compressed and that made the whole thing jam. There's just too little room inside the body so had to make a design change and move the return mechanism outside the body. This is how it was originally:

    [​IMG]

    And after moving the return mechanism (in this case a rubber band pulling a lever) outside the body this is how it looks like:

    [​IMG]

    Also improved the stock and added the piece that will later on hold the crossbow prod in place. It's still missing a cheek rest, rail for the red dot sight and the whole spanning mechanism. But after those it's pretty much finished. Thank god I don't need to worry about the trigger anymore, really started to get on my nerves... :rolleyes:

    -allu
     
  11. allu

    allu Junior Member

    133
    0
    0
    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):

    [​IMG]

    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 :p 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)!

    [​IMG]

    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:

    [​IMG]

    [​IMG]

    That's all for today. Thanks for reading :)

    -allu
     
  12. slingshot_lover

    slingshot_lover New Member

    479
    0
    0
    Looks good so far ;)
     
  13. Petebacardi

    Petebacardi New Member

    127
    0
    0
    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??
     
  14. allu

    allu Junior Member

    133
    0
    0
    @ slingshot_lover: Thanks! :)

    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.
     
  15. Petebacardi

    Petebacardi New Member

    127
    0
    0
    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.

    Cheers
     
  16. allu

    allu Junior Member

    133
    0
    0
    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:

    [​IMG]

    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:

    [​IMG]

    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:

    [​IMG]

    [​IMG]

    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
     
  17. RalphG

    RalphG Member

    218
    0
    16
    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?
     
  18. allu

    allu Junior Member

    133
    0
    0
    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. :rolleyes:

    -allu
     
  19. Isakpettersn

    Isakpettersn New Member

    40
    0
    0
    Would you be interested in selling the original cobra without the spring?:)
     
  20. allu

    allu Junior Member

    133
    0
    0
    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 :D (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 :)