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Oodalump's guide to performance K'nex guns Answered

I just think this needs to be brought up again and seen some more.  Lots of very useful information in here for both new and experienced knex gun builders.  And no this is not outdated, do not look at the post date.  That is irrelevant.  

Here you go, read through all of it.  All of it.

This guide helped me a lot, and should help everyone else as well.


Can someone with access to KI Ctrl+C Ctrl+V ?

Idea time: On the swag boss try putting a black rod then tan rod as the two firing pins then make the rest default. wouldn't that be like a two shot burst? Keep in mind I havent built the swagboss. This will work if the rod goes out long enough. I think the turret will have to be modified a little or else turn it into a double sided mag. Its worth a try. A war worthy BURST assault rifle.

Depending on if you blocked the pins in the same spot, it wouldn't make a difference.

Did you mean to put this in Zak's thread? And if I remember correctly, it already had a two stage trigger that allowed the shots to be separate. If not, it wouldn't be hard to implement. But making different length pins would not be the best way to do it.

Kk. I am posting MY version of something like that. Spent a few hours doing it. Pretty nice actually.

The swag boss already had the ability to be "burst fired", although could always be improved on.

The only thing that I really found incorrect is the statement that heavier pins add range. I discussed this in my concept automatic chambering weapon. Basically, an object with less mass than an object hitting it will only ever travel roughly as fast as the object hitting it. Now, there are factors such as compression and elasticity that also come into play, but for the most part are negligible (especially with stiffer black rods) because faster moving firing pins (or heavier rounds) will actually cause more compression anyway. Anywho, if you imagine a pin and a round coming into contact in slow motion, you'd see the pin hit the bullet and slow down ever so slightly (probably not noticeable depending) because it's transferring energy into the round. Then the round would start accelerating. Now, it really depends on bands and other factors, but at best, the round will speed up to the speed of the pin and then they fall out of contact as the pin hits the gun. There isn't any magic where all the energy of the pin is transferred into the round.

That was a long post so let me just get to the point if you'll trust me without reading:
Lighter, quicker pins are better. In fact, having a pin that is lighter than the bullet (but don't use a heavy bullet) would be optimal because it'd transfer all of its momentum. If someone could build a rail gun to test this for me, that'd be great. Make a rail with a pin as light as possible. Then also make a pin, without affecting its length to the bullet, that's a bit heavier.

I see what you're saying, but that just doesn't seem right. A bowling ball would go farther if you swung a sledgehammer slowly into it instead of quickly hitting it with a regular hammer. I want to go to the hardware store and buy a metal dowel that is the same width as a knex rod and make a firing pin out of that just to see if my guns would work any better with it. Would be interesting to see.

Do so.
And you're thinking with too many other variables. For example, is gravity assisting you? Or are you swinging perfectly horizontal? Also, a human can only swing a regular hammer so fast, probably not with the same momentum as a sledgehammer.

Either way seems plausible to me, having a heavy/light pin being better. I guess I should find out if I do the metal dowel thing.

force x time = mass x change in velocity.

As far as Knex guns are concerned, "Time" is how long the pin and ammo stay in contact. This time comes from the compression/elasticity of the materials. A metal dowel doesn't compress as much as a plastic rod. The time would be less for the dowel, so I wouldn't expect it to shoot farther than a gun with a black rod.

And just for the fun of it, more Knex gun science!
But by this logic, a gray rod should be better than a black rod. A few years ago I did this experiment and tested both. The black rod won despite the math. A gray rod should be traveling faster than a black rod because it weighs less. The impact time should be greater because of the higher speed, and because the plastic is more elastic. I came up with an explanation for why those factors didn't help the gray rod.
It comes back to the F x t = m x dV. Both rods travel the same distance, but the gray rod moves faster. That means that the rubber bands don't apply force for as much time as they get to with a black rod. The gray rod doesn't get as much energy.

Coming up with a formula to find the best weight + elasticity would be a waste of time when we only have a few rods to choose from. Everybody already knows that black rods shoot stuff the best, so that is why we use them.

In the end, we were never having opposing ideas, only trying to explain why it is we shouldn't have heavy pins. Yes, I agree black rods are the best. And I retract my statement that lighter pins are better because they flex less and would probably reach a maximum velocity given that bands can only retract so fast.
I was, however, trying to hypothesize whether having a short pin with a lot of bands to accelerate as quickly as possible was also viable. I assume you tested that, though. And even though it'd make for a tedious pull, it'd be a short one which then could possibly be aided via leverage such as with a lever action, something that isn't as viable with longer pins. This would offer increased RoF without sacrificing much range. But I don't truly know whether this would work out or not. Still, I'd like to see someone try it out. Maybe I'll give it a shot just because I'm curious enough and have free time next week.

when I was first going to make a chain gun out of K'nex I wanted it to shoot fin ammo and I wanted it to shoot hard and fast. So the idea was to create a "bullet" with the projectile and firing pin primed that was a yellow rod contained in a gray rod length "bullet" With a ton of bands I did achieve decent velocity however It was kind of a pain but with a pump or something it may work good. Or in the case of preloaded "bullets" like on a mg the idea isn't bad to conserve on the size of the chain use to propel the chain gun. I still want to build a chain gun one of these days lol I never finished the project due to the limited number of pieces I had but I always thought it would be awesome to see a K'nex gun shoot fin ammo 250ish feet fully auto! lol
The chain would have to be 50 rounds long or so with quick and easy reload but man one of these days I'll make an awesome MG.

Well again, a lever would probably be best because it's using the exact principle needed--leverage. Turning a small distance with a lot of force into a larger distance reduces the force required. That should make a small pin with a lot of bands much easier to cock. Also, it would allow for a gun with a great RoF.

And the MG sounds pretty cool. Even if it's impractically large or somewhat unreliable, the idea of sending 50+ rounds down range would be awesome. I remember when Gatling guns were the rage but they all had subpar range.

Another idea I had a while ago that could be similar was a sort of K'nexsayer Ooda gatling gun hybrid. Several barrels but one pump that can cock a barrel and then revolve the cylinder. So in effect you have a sort of "water gun" action where you can pump multiple times for multiple shots. It would probably be a complex mechanism, and it'd still require manual loading of rounds, but it'd offer an excellent balance between RoF, rate of charging, and range.

Not really what I meant. For sake of simplicity, I'll use 8 barrels in my example. Well, I pretty much want an 8 barrel Gatling gun. Except instead of having to prime each barrel separately, you could use a universal pump that charges an individual barrel and rotates the barrel so you charge a new round with each pump until you've pumped 8 times or any number of times less than that. Then unleash them semi or fully automatically.

I don't get your goal here... But no. His charges three shots in one pump and no more. My idea is 8 separate charged shots and you could charge them one at a time via a pump. The idea is to still get good range. The pump is more of a convenience in reloading the weapon after firing all the shots.

I get a lot of those ideas. You first experienced that when I proposed to SK a bottom loading bolt action weapon built specifically for range. You seemed to like that idea, though, yeh? Wasn't too crazy. Kinda practical actually. You build anymore, Zak? Should really if you don't.

Oodalumps/piot and I had a skype call going where we were going to bust out the plastics and build something but it didn't really happen, ended up just playing games haha. I'm thinking about it.

Awesome. I'll admit, your ego bothered me for a time, but you're sounding fine again. You were a great builder. And to answer your other comment in this one, I'd suggest making a V3 of your ZKAR. I know Mepain essentially did that for you, but see if you can make your own removable magazine version that's a little more compact. Redesign the trigger to not need hinges and to hold a good amount of power as well as just a general tune up. Just a suggestion, do whatever.

I'm not really sure if removable magazines have a place in wars but perhaps I can try that again. I dug up an old pic of mine too: http://i386.photobucket.com/albums/oo306/ZaKnex/Picture397.jpg

If oodammo fast mags have a place in wars I don't see why normal removable mags don't.

Well the thing about oodammo mags is that they're very compact and low maintenance. Magazines, especially yellow rod ones, can be a bit more cumbersome. So, Zak, this is actually a tactic rather than just a gimmick, make yours hold a magazine in the stock like my BAW did. And if still possible, you can make it have a quick loading side gap to load individual rounds. Another idea if you want to be more daring and get the best of both worlds is keep the fixed magazine, but instead have a side either mostly open or swing open and then have a K'nex speed loading clip of yellow rods all lined up so you can insert them all in one go.

The first 2 actually are easily feasible by today's standards I think, I haven't knexed in a long time so I'm rusty and wouldn't actually be able to design it myself though.

Ok I think I get it now. That sounds really big and complicated.

And it is. But that's what the K'nexsayer was too when it's much simpler to just use a pump TR weapon. I wouldn't ever attempt it and I'm not at all surprised if no one else ever tries. It has potential, though. Just a concept.

Yeah but I wouldn't want a gun much bigger than a TR for a war anyways because then I would be sacrificing a lot of speed/maneuverability, as well as having it probably be less reliable. From what I've seen of the wars on youtube, it's all about running and gunning, for which the TR is perfect for.

Well yeah, the gun would be mostly for fun. However, I do feel like a small enough version could be made. Anywho, the TR feels like overkill. You're correct, it was a lot of run and gunning, so what's the point of trying to squeeze every little bit of range out of the weapon? A pistol would offer the best mobility and ease of use. Or rather we should develop more shotguns and high RoF weapons.

IDK about you, but I wouldn't want to be within 30' of someone else with a gun unless I snuck up on them to shoot them. Range is always a good thing. My backyard is 55'-60' long or so, and my TR with 4 bands will just shoot oodammo across it with a slight angle and still hit hard enough to feel. And my backyard looks pretty small. Less power wouldn't be that great. Indoor wars though, I could see a TR being awful.

I hope I can make it to this war just to test out whether it's that important or not. Instead of preparing a long comment on range, I decided I'm just gonna make a forum post eventually about my thoughts on war weapons. I'm busy tonight, but I'm gonna test some ranges with my pistol with different bands when I'm free this weekend. I'll compare these to TR ranges I here. If you want to help, I want you to take some very specific, very accurate measurements from a TR-like weapon:
Measure the distance of the bands to the pin as well as how you attach them (single or double stretched). And then increment the amount of bands you use. Then fire flat measuring from the front of the ammo to where it lands down to the inch. Measure the extremes (minimum and maximum) and then the average of all the shots. You can just do them in sets of 8 just to be simple. This is just range which is mainly what I need accurate data for, but if you want to go the extra mile, then time how long it takes for you to fire off 8 shots in rapid succession accurately. I don't care what definition of accurate you use, I'll use the same. Finally, time how long it takes to fully load the TR from an empty state with ammo in your pocket or however you'd carry them in war.

At a war, you're almost never going to hit someone at 50feet. But the point of a gun shooting that far is that at 35-and-under, the targets are much easier to hit if what you're using shoots 50 or so with oodammo, which is what's important. If you're 50-60 feet away, you're not going to be having fun anyways.

I would say 50ft was average engagement range considering in testing the other day the TR was shooting fin ammo about 100ft or more it really comes down to the ammo but given oodammo is a common war ammo 50ft is minimal war gun range outside.

The other reason they are good is just that they are so reliable. Most other guns that I have built tend to jam/have trigger issues much more commonly than the TR. The only gun that doesn't do it nearly as much as others(but still not as good as a TR) is my modded ZKAR. And I would like to do a lot of those measurements, but I'm going to be gone for a week and a half at my aunt and uncle's starting today, and then school starts, so we'll see. And with reloading, I wouldn't fire until empty and then reload, I would just be constantly reloading and winding the turret whenever I have the chance. I feel like it would be pretty rare for you to have to fire off all 8 shots without a chance to reload at all.

The main problem with something like my zkar is the reloading during a round of a game for sure.

I don't know if this is just a problem with mepain's bullet lock, but sometimes the rod won't get pushed all the way up flush with the top of the barrel and the ramrod won't hit it. And yeah reloading is slow.

His that uses hinges instead of a grey connector and broken Y clip. Idk if it's worse or not, but it doesn't use broken parts, which I like.


Hm okay, never had any problems with mine. That picture I linked had a faster on-the-fly reloading system and stuffs.

Yeah I thought of that once just never got to building it so many other cool things I would rather build I guess


I agree with this for the most part. Lightweight pins traveling at high speeds will shoot further than a heavier pin. Less force to move the lighter pin and transfer a greater amount of energy.

Ah, I remember this guide. 'Tis very good.

I am fully aware that I'm necroing a month old post. :I  I was just that bored.