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Old 12-05-2015, 08:38 PM   #1
allu
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Hi all!

Decided to start one universal thread for my projects as I don't feel like having several threads covering the same area: crossbows. So I'll post all my current and future projects here, easier to find and easier for me too.

Earlier threads:

Flipper style crossbow
Flipper style crossbow version 2
Cobra pistol crossbow modding

Yesterday I challenged myself to turn my cobra pistol crossbow into some sort of flipper. Well that kind of failed before it even started, couldn't find any suitable materials. Plywood was too flexible at required dimensions and didn't have small enough steel square pipe. Could have worked with different design, but didn't feel like stopping there. The parts from my old version 2 flipper were still intact and available, so decided to build a simple survival crossbow flipper thing instead

allu's projects - Slingshot Crossbows

allu's projects - Slingshot Crossbows

Made it as simple as possible, and while it looks ugly it functions just fine. Well, as fine as it can, the trigger is really primitive and the whole thing is kinda clumsy due to its sheer size. Draw length is around 70 cm (~27,5 inches). About the performance, well, it did fire once before the arrow bounced of the target and disappeared into the snow -facepalm- Man I never learn, sharpen the point and make them stick to the target instead of having them bounce off and zip into the snow. So the performance testing gets to wait for a new arrow

-allu


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Old 12-07-2015, 01:21 PM   #2
allu
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After a long time took my trusty cobra pistol crossbow and went out to shoot with it and had a blast! It's so much fun to shoot even if it doesn't pack that much of punch. But that's what I'm going to change next. Found a perfect sized piece of fiberglass pole (from an old kids' bow) and we'll see if that can be fitted behind the original prod. Probably won't do much but you never know!

Just to make comparison possible arranged a quick test, shot from 10, 15 and 20 meters with the lighter bolts and then at 20 meters with my homemade bolt. Took a few tries to hit with the homemade one, it's so heavy that at 20 meters the bow really struggles to launch it that far. Aiming point moves like 1 meter upwards compared to the lighter bolts. Target was a piece of 7 mm ply and here's the results:

allu's projects - Slingshot Crossbows

Original bolts:
-Lowest pierced and went through, shot from 10 meters.
-Middle pierced but didn't go through, shot from 15 meters.
-Highest, barely pierced, shot from 20 meters.
Homemade one:
-Straight through with ease, mass really helps with penetration. Would penetrate even better with a sharper tip.

Hopefully the mod works and I can start shooting bigger bolts out of it, because who doesn't like extra power? If the results are encouraging maybe I'll even make a stock for this to increase stability and accuracy. (Just turning my thread into a blog, oh well I like writing down my thoughts )

-allu


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Old 12-07-2015, 06:04 PM   #3
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Watching this study closely. Enjoying the results.
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Old 12-08-2015, 12:42 PM   #4
allu
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Quote:
Originally Posted by bigdh2000 View Post
Watching this study closely. Enjoying the results.
Glad to hear, always nice to get feedback!

Well it turned out the fiberglass pole wasn't ideal after all. It was shaped more like a circle than a flat piece, so it didn't want to bent too well. It was possible to place it behind the original prod, but when I tried to string it it let out a loud cracking noise and I forgot the idea altogether.

Next idea was to use pvc. Well I got it working:

allu's projects - Slingshot Crossbows

But there's some weird black magic happening. It loses most of its power after a handful of shots but next morning it was fine again for another few shots. I guess it rather changes shape than works as a spring, so I guess it's time for a third try. But I have to say the bolts were speeding out of it while it was working well, and crashed straight through that 7 mm ply. Well it was fun as long, or should I say short, as it lasted

Although pvc didn't work out too well it still gave it a small but noticeable performance boost. This time I was testing at 10, 20, 25 and 30 meters. Using three different types of bolts: original full aluminium and aluminium with plastic fletching bolts and of course my homemade one. Again target was the same 7 mm ply but this time I also paid more attention to accuracy. Here's the results:

10-20 meters the heavy homemade one dominates, the lighter bolts are no match.
20-30 meters the second heaviest original bolts with plastic fletching are the best.
+30 meters the lightest bolts win.

This is pretty confusing My theory for this is that after 20 meters the heaviest bolt requires such a high launch angle that it loses most of its kinetic energy on the way up and on the way down gravitational pull isn't enough to make up for the lost speed. At 30 meters the same happens to the second heaviest bolts and that's why the lightest bolts carry most kinetic energy at range, but not up close. Just my idea, feel free to correct me if I'm completely wrong!

When it comes to accuracy the original bolts can't compete with the homemade one. Those cheap bolts just can't fly straight, they're fine at short range but at 30 meters it takes like five bolts to hit the target. Not because of my bad aim but just the inconsistent flight pattern. On vertical axle they pretty good, but on horizontal axle they just fly left or right, maybe three of my 17 original bolts fly dead straight, made in china quality But I'd still pick them over my homemade bolt simply because it's ridiculous to have the arrow flying like 3-4 meters high in the air on the peak point, and while it flies straight on both axes, it's still really hard to compensate for the drop

Any suggestions for how to increase its performance? Feedback is always appreciated

-allu

Last edited by allu; 12-08-2015 at 12:46 PM.
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Old 12-08-2015, 06:42 PM   #5
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Can you get a replacement prod for the cobra? Over here these are between 10-12€. Cut it short, about where the arms begin to make the outward curve and use this instead of pvc. Make sure to round off the ends of the short one properly, other wise the longer prod is prone to break at where the inner, shorter one ends. This should almost double the power at least rise it a considerable amount. Since the trigger is just pushing the string out of a groove AFAIK it can take the weight. If the spanning mechanism can take it, I don't know.
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Old 12-08-2015, 08:55 PM   #6
allu
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Yeah I've seen someone add another prod on their Cobra with great results! He got like 235 fps out of it. But I'm so short on money right now that can't afford to buy anything, but hopefully I'll manage to land a job tomorrow (going to a job interview, eek) and one day I can afford it

I have too many projects going on at the moment. It felt wrong to see my first flipper just lying there in the corner unused simply because the stock doesn't really stay together. The mechanism itself had nothing wrong with it, so I got this crazy idea to combine the swing arms and the failed cobra pistol crossbow stock. Though that sounds like awfully lot of work, so most likely I'll make a super sturdy survival crossbow out of it, mount it on a piece of 4 by 4 wood post. So a pretty similar concept to what was shown in the first post, but this time with a bit more sophisticated trigger. Either medieval or something a bit more modern. Something similar to what Joerg used in his Leach trench catapult could work too, since it would allow the arrow to be separated from the stock making any sorts of rails unnecessary. That'd be a big plus since I don't really have any tools that could carve such rail into a wood post easily.

-allu

Last edited by allu; 12-08-2015 at 11:13 PM.
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Old 12-09-2015, 11:58 AM   #7
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Surprisingly the flipper was able to shoot the bolt I made for my Cobra pistol crossbow. Accuracy wasn't the greatest since the bolt had some play on horizontal axle (the bolt groove was too wide for it), but still accurate enough to hit the target at 30 meters. Man the bolt flew fast requiring minimal launch angle, definitely faster than my cobra These good results really encourage to built a new stock for it, some parts should be reusable too. But tonight I won't have time for that, job interview is more important and as Joerg said, in life you have to set your priorities

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Old 12-11-2015, 09:32 PM   #8
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Having got a job now I'm able to spend a little bit on my projects as well. Cobra pistol crossbow was on sale for 20€ so I bought another one

allu's projects - Slingshot Crossbows

Obviously I had to try using the old prod behind the new one to boost performance. Everything went fine until I had to string it. Man it took me a frigging two hours to get it done and lots of frustration, such a pain in the ass, seriously. But finally I got it done and realized the edges of the old prod are cutting into the string slightly. No idea if it's enough to actually snap the string or does it just make it wear faster, no idea but time will show. Cocking it was a lot harder than before but still manageable, although the rail, in which the foregrip was attached, was torn off on the process. Chinese quality aluminium, oh well Luckily I was able to attach the rail again.

I got it working around 10.30 at night, so obviously wasn't going to do any outdoor shooting. But at point blank range the results were promising:

allu's projects - Slingshot Crossbows

allu's projects - Slingshot Crossbows

7 mm ply was no match anymore so had to go up to 9 mm. Even that was pierced by both bolts! Can't wait to shoot it at distance tomorrow, just hoping it won't snap the string anytime soon. But if it does then I'll modify the second prod slighty, just by cutting of the tips all together so that they won't get on the way of the string. It should still give a nice boost. The reason why I'm not doing it now is simply I have no interests to fight with the string again, it's seriously a pain to take off and put on lol. That's all for now, more tomorrow!

-allu
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Old 12-12-2015, 08:24 PM   #9
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Approximately 50 shots fired with the new configuration and everything is working fine! So far so good. Apart from my red dot sight that had its battery die at the very moment, so had to switch to original iron sights, they're quite terrible honestly.

Man this thing is on steroids right now The speed difference is huge, original bolts fly with a super flat trajectory up to 30 meters and hit way harder than earlier. Not sure if that's a good or bad thing though, 7 bolts were killed in action today Most had their tip torn off while trying to remove them from the plywood, or my house's wall, whoops

Well some pics of destruction, first 7 mm ply from 15, 20, 25 and 30 meters:

allu's projects - Slingshot Crossbows

Then 9 mm ply. Was only able to hit it up to 20 meters due to it's small size (and the lack of red dot sight):

allu's projects - Slingshot Crossbows

Again same 9 mm but this time with the homemade bolt from 20 meters:

allu's projects - Slingshot Crossbows

Then a trick shot, managed to hit a rope (from clotheshorse) and the fletching stopped the bolt there

allu's projects - Slingshot Crossbows

Also the rail for foregrip didn't hold up so no foregrip anymore, hence even more inaccuracy. It shoots beautifully, but I have to say it's pretty inpractical at the moment. It's just painful to load, not bad for dozens of times but once you start reaching 50 shots in a row your hands and elbows are burning. A stock is a must now, maybe even some sort of fore grip if it's just possible to attach one to it. Hopefully I can find batteries for my red dot sight and do some more accuracy testing!

-allu
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Old 12-13-2015, 08:34 PM   #10
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Got this done today:

allu's projects - Slingshot Crossbows

So much more comfortable to shoot and feels much more stable too. The iron sights are way too low though requiring quite an awkward position to actually see through them, but a red dot sight will solve the issue. Also figured out a new way to cock the crossbow without killing your arms: press the shoulder stock against your chest sideways, take a firm grip of the upper section of the stock, press the lever to release the cocking mechanism and pull from the "grip" (in front of the prod) with your left arm. Absolutely no effort at all and real quick Going to paint it black once I have time from work, most likely not until Wednesday. More about this then.

-allu


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