Bullet bow with a rifled barrel - Discussion & Project planing

First topic message reminder :

I'm stuck at work guys..and just happen to be stuck at the computer

A bullet crossbow has been on my mind for a long time and we've discussed the various types with their pro's and con's, so a barreled bullet bow is what stuck in my mind. There are active discussions on the net regarding the rifling in these bullet bow barrels, but no one seems to know for sure whether rifling will be useful in a crossbow and even further from actually attempting to cut some rifling to test it out.

So I decided to give it a try by starting out with the assumed to be "the hardest part" - Barrel rifling jig.

Here is the jig drawing...nothing revolutionary...just a rod with a cutter secured at the tip and a piece of aluminum or steel tubing with a guide slot cut in it...it is a pull through design since pushing it can get things flexing and I don't want that.




The first problem I encountered was kinda pathetic, but damn it ...how the hell do you plot the guide slot on a round surface...well you know what they say...if you can't do with any other tool...there is always "ductape".

Well...masking tape will do just as well...so plot the slot outline on a piece of tape and just roll the tube in it..then dremel the hell out of it...that's my solution.



The cutter head and the connector are still in question since I have to account for metal chips that might clog things up and make my life very difficult, so suggestions are welcome.

How about something like a screw in choke like some shotguns use. Screw it off to reload, screw it back on, 6 inches or rifling.

Interesting thoughts guys!
Basileus...do you mean a turbine?

I took apart quite a few dental air turbine powered high speed hand pieces for maintenance and repair. I agree - consistent airflow is a must.

Thinking perhaps the aggressive rifling isn't such a bad idea...as the deeper grooves will supply the necessary flow of air for the turbine blades/air tunnels to take advantage of. Hmmm...very cool stuff!

As for connecting it to the string...I think a ring to house the turbine assembly with "tear drops" on both sides of the ring for the string to attach to.

Spoiler:

Mmmm...I'm thinking super aggressive(almost falt) turbine blades....sounds so high tech. Thumbs up basileus!

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I was going through another interesting variations, in fact one that was very similar to the offset string slots you guys mentioned. A "hop-up" barrels used in paintball/airsoft guns. An example here is "Flat Line" barrel used with Tippmann paintball guns.



...and perhaps a somewhat exaggerated, but still decent example of the idea.


Instead of a spiral spin indused by the rifling, the barrel gives the projectile a backspin that keeps it gliding on body of air.



There is an interesting article I found online about this effect being tested with airsoft guns using hop up barrels:

http://mackila.com/airsoft/ATP/03-a-01.htm

Just throwing out yet another cool bit of information.

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Warhammer1,

About the string angle...do you mean using angled lever axis to change string angle/hight as it travels along the track. This does make sense in a hop up/spiraled groove system and actually sounds like a viable solution to string wear.

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I know I kinda made a mess here trying ot combine everything into one post, but what do you guys think?

Regards,

Ivo

the hop up barrel might be a good idea. I think the results of rifling would be a little bit of a let down, as you would need to have the ridges bite into the bullet to get much use, or use a patched ball like in a blackpowder gun. I think it might eat a little to much of the energy from the cross bow. If you are going to try it, try to get your hands on a book called guns and gunsmithing tools of southern apalachia. it has many photos of home made rifling setups. it also has a section on crossbows in the back that is interesting. the book was written by a man named John Rice Irwin who runs a small frontier culture museum in Tennessee. I also recall that one issue of the fox fire book series has a good set of articles on gun making. Used to be a hobby of mine, but the guns were to loud. I just stick with archery these days.
Jamie

Thanks for the info vabowyer,

I know rifling is a bit useless with crossbows, but rifling a barrel is still an interesting subject and might come in handy in this project one way or another, so I'll see if that book is available through my library.

Reading up on Magnus Effect, it seems to be way more applicable to crossbows than rifling is. However I'm a bit stumped after reading this bit of info: "Rifling is better for horizontal accuracy, hop up is good for vertical accuracy." Would that mean the weapon will have to be perfectly level for hop up to be accurate...if at all useful?

Ivo

PS: I love guns...I hate how loud they are...and what upsets me the most about the whole situation is that silencers are illegal.

Spoiler:

Ivo wrote:Would that mean the weapon will have to be perfectly level for hop up to be accurate...if at all useful?

Any crossbow is more accurate if it is perfectly level, so that doesn't sound like much of a hardship.

Mac

In my humble opinion:
I think the point is hop up barrels put a back spin on the projectile corresponding to the pitch axis, like a basketball. Good for low speed projectiles because it dials out some of the correction for gravity. Rifling spin is around the yaw axis so it dials out horizontal variables but you still have to correct for bullet drop.


"Any crossbow is more accurate if it is perfectly level, so that doesn't sound like much of a hardship."
This means the crossbow tips must be kept level, along the roll axis. Allow some roll and your shot will wander off to the downhill side.

Where would I be without you guys.

mac wrote:Any crossbow is more accurate if it is perfectly level, so that doesn't sound like much of a hardship.

Mac

Mac, that one really made me smile. +1 Rep for you Sir.

8fingers wrote:I think the point is hop up barrels put a back spin on the projectile
corresponding to the pitch axis, like a basketball. Good for low speed
projectiles because it dials out some of the correction for gravity.
Rifling spin is around the yaw axis so it dials out horizontal variables
but you still have to correct for bullet drop.

Yep, that's what I'm talking about and couldn't put it better.

The level issue I'm talking about is with hop up the spin axis must be level with the ground for the Magnus Effect to be beneficial to accuracy. Since I don't have much experience with aerodynamics calculations and have to go by feel here, I believe if the spin axis is not perfectly level with the ground...the differing air pressures surrounding the projectiles will also be offset and reduce or even cancel the benefits of hop up. Here is how I "see" it...

If we take a back spun projectile and compare it to an airfoil, we will see that there is quite a few similarities. Now we picture that the perfectly level to ground axis of the back spun projectile is the same as the wings of a straight gliding plane wings. For the plane to glide straight, the wings must be level to the body of air that it glides on...as soon as one wing is lower than the other the plane will begin to slope and start to lose altitude...this same phenomena I imagine with a back spun round. If spin axis is not level, the projectile's trajectory will change dramatically as the projectile will fall faster and to the left/right depending on the degree of cant of the weapon.

Of course it would be cool to develop a completely independent self leveling mechanism that would induce back spin on the projectile as it is being accelerated traveling down the barrel , but this is all jibber-jabber...mambo-jumbo...talk yourself into a corner approach...and perhaps it's time to try it out on a more realistic level.

I guess I'll start with a concave plunger with a magnet embedded in the center to keep the projectile from interacting with barrel wall, a simple bubble level for reference, and a hop up barrel choke that uses a rubber lip to induce spin on the projectile.

Sounds doable?

Ivo

I'm with ya' as far as the bubble level. I think the Swiss target shooters use them all the time.

Mac

My sons play paint ball and use hop up barrels. By rotating their weapons horizontally, they can shoot around corners.
Anybody up for some trick shooting?

Hmmm...I don't know about curving around corners...that basically means that there is toooo much hop-up , but certainly a cool trick and with an adjustable hop-up it would simply be a shame not to try this out.

Can't remember when was the last time I played paintball, but I do remember being the only guy left on my team, running low on co2/ammo and starting to freak out as I was being cornered by three people into a ditch full of crap. Came home polka-dotted with welts and happy to boot - just the though of taking as many of em out as I could before they finally got me jammed in that ditch...hated those full auto's they had , but loved the last shot I got in on them(oh, did the paint spray through the mask and into your mouth?)...bitter stuff that paint is.

OK...To get back on the subject of hop-up module...I did a bit of digging and thanks to good people I found a few interesting videos showing the:

assembly



testing/research



And finally a very inspiring bonus...titled: "Golf ball Shot Across Canyon - Hop-Up"



The question that comes up is - In airguns the hop-up is right at the beginning of the barrel, but how about crossbows?

...I'm thinking the end of the barrel makes the most sense ...any thoughts?

Ivo

Found this video and thought it might be inspiring.

Nice video 8fingers. Makes me want to learn Russian, though I think I could pick out the word for crossbow. (Arbalet? or something similar, my spelling is going to be way off)

So at around the 5:30 mark was that crossbow a convertible crossbow? Add a top piece and it can fire bullets, remove it and its back to a bolt firing crossbow?

That is what I thought I saw, remove barrel and driver from stock, screw into place and shoot ball bearings.

I've heard about that crossbow. Unfortunately the video is a bit misleading.

The barrel that slides on top of the arrow track is in fact a "magazine" that holds the ammo. Once the crossbow is loaded, a ball drops from the mag onto the arrow track right in front of the string...or perhaps it's fed under a retainer clip by a slightly more sophisticated mechanism as the crossbow is spanned....but in the end, little was done to make this bow an accurate bullet-bow. The ball is brutally pushed along the arrow track by the string. God knows where the string jumped when contacting the ball...can be under the ball *bringing it in contact with the mag* and the ball will be rotating backwards - getting lift...or...string jumped higher and the ball is now pushed along the track and is rolling forward - making it drop faster.

I mean...I just read it's not very accurate and I'm trying to understand why.

It is a pretty cool crossbow though. The platform chosen for this bow is a simple pipe...starting at the riser and housing/or in any other way helping retain every other component, ans even ending as a cheek rest.

http://talks.guns.ru/forummessage/55/391789.html



- Not Resized



- Not Resized

Still... there might be a chance that they had the right idea of not using an actual barrel to push the ball along.

Maybe a few small additions will make that bit actually beneficial...gotta let that roll around in the head a bit.

Ivo

This does not use a barrel but you can shot lead balls with it.




Todd

Wish I had found this some years ago, and sorry to post to such an old one, but...

Regarding rifling cutter depth:  I saw a rifling cutter supposedly used for making Kentucky Rifle barrels in a museum about 35 years ago, and the placard said bits of paper were added under the cutters after several passes to increase the depth of the cut.  

Regarding the bullet engaging the rifling and friction, a lubricated patch would be most probably work, and the right combination of precise balls/bullets/projectiles and fine cloth should help reduce friction.

Regarding the string engaging the projectile, many airguns use a plunger.  Why couldn't the barrel and breach be mounted more forward, and the bow (prod?) mounted behind the barrel and the draw kept to a minimum, so that a plunger could be used.  That would eliminate the need for a "pass through" design for the string within the barrel. The plunger should also have a freely rotating head to reduce friction.

The design I'm thinking of would need to be loaded from the muzzle with a rod, like my black powder rifle.

Some years ago,a language arts teacher in the Appalachians started a magazine,using his students as reporters and editors.The result of this,was extensive interviews by the kids with local old timers on country crafts,and ways of making and using everything from toys to rifles.This program was so successful,that it resulted in a series of books titled Foxfire.The books were numbered from 1 to 10.Foxfire No.5 is the one you want,it covers 'ironmaking,blacksmithing,flintlock rifles,and bear hunting.there is extensive info. on how to rifle musket barrels using tools that you can make yourself,mostly from wood.
                                  Hermit.

Geezer here, commenting on rifled bullet-bows.  Not that I'm terribly interested in making such a bow myself, but you don't HAVE to use steel for a rifle-barrel on a bullet-crossbow.  One could drill and then rifle a billet of hard, greasy plastic, like Delrin... same process as with a steel barrel... drill it on a metal-lathe, then cut grooves.  Then you make your projectiles with a special studded collar that fits the rifling precisely.  Perhaps that could be cast, or even machined, again in a hard plastic.  That way you'd get a precisely fitted projectile running in a low-friction and low-weight track.  What a challenge, non?

Interesting thread though I didn´t have the time to read it carefully.

But I need to say that there will be no barrel rifling needed with crossbows.

Rifling is to bring a bullet due to tight into rotation.
Every projectile would benefit from this point. (see spin of bolts arrows and projectile ballistics)

But against the Gunpowder powered systems a crossbow does not benefit from/or need counter pressure after release.

So a barrel should only prevent your crossbow projectile from leaving its way for a relative short amount of time. This evolved by the difficulty of building proper working splitstring bullet crossbows (italian and german "schneppers" for example) and come along with a loss in firepower due to the barrels friction.


You would not want anything that slows down your projectile with a crossbow.
The barrels of the original guided crossbows will have a relatively loose fit I bet.

The plunger idea as another problem, too.
Unless you build your planned barrel a lot longer than your "bolt-track" you will be loosing acceleration distance.
Second con is that plunger will weigh something, which leads automatically to a loss of energy that can not be transferred to the projectile again.

Hope I expressed my thoughts well enough to be understandble in these early morning hours, gotta go to work.
Bye Rizzar

Rizzar:  your points are indeed clear, and right on the money.  Adding rifling with a tight bore to a crossbow, particularly with a plunger, only costs energy, whereas a properly fletched bolt/arrow already has the spin without the obvious cost.  Still there's a group out there who still toy with the concept, so I thought i would provide a little thinking outside the box.  If you're not subjecting the 'barrel' of a bullet-bow to high internal pressures, it's not necessary to make it of steel, and since studded projectiles were used in some 19th century artillery, making studded, low-friction projectiles might help overcome some of the obvious friction-problems.  If the projectile is properly shaped, it wouldn't need a plunger. 
Then again, how about a discarding-sabot projectile for a bullet-bow? Again, we have lost energy through the sabot, but the internal dart could be a hum-dinger! 
Geezer, just thinkin'

I think you guys are correct in the above posts. I will just add that I have made my own rifled barrels from scratch for Black Power rifles including boring out the barrels, reaming and rifling, and building the rifling machine. It was a major project to say the least that went on for several years.
And as stated above by others I don't think it would be practical for Xbows. Just think about the relative forces involved. Even BP rifles have working pressure around 10,000 PSI. So for a 50 cal barrel, that is close to 2000 lb of force on the bullet!  It actually deforms the bullet (or round ball/patch) and forces the lead into the grooves, and engraves the bullet. I cut my grooves about .012" for patched round balls. For my tight fitting round balls with lubed patches, it took about 30 LB of force just to push it down the barrel. That kind of tight fit and deep (compared to jacketed bullets in modern guns) was needed to keep the ball/patch from "skipping the rifling" because the spin up was so fast the inertia of the bullet was huge. Like from zero to 200 RPS in 4 Msec. Or an acceleration of 43,000 RPS /second.   
We just aren't going to get those kind of forces out of a an xbow. In fact I guesstamate that it the BP rifle uses more power just to spin the bullet than we get out of a Xbow!
And at the relatively low velocity we get with Xbows, it would have very little effect. Some but probably not noticeable.
Just my 2 cents. . .
John

Yep,does',nt matter which way you cut it,there is more power obtainable from expanding gasses,than from a spring.If this was not the case,development of bullet firing crossbows would be much further along.Personally,I would think that adding rifling,even shaped sabots,would take away so much power that the performance would be at best,dissapointing.
                                                                Hermit.

jaeger22 wrote:
We just aren't going to get those kind of forces out of a an xbow. In fact I guesstamate that it the BP rifle uses more power just to spin the bullet than we get out of a Xbow!

Well, usual "UK-legal" air rifles have only 7 Joule muzzle energy. Friction issues should not be exaccurated.

And of course crossbow barrell does not need to be gas tight. I have been thinking about these and IMO the way to go is square or oval barrell with slight twist at the end.

As far as "plungers" go- one possible and quite effective approach would be medieval bat-springald: string does not push bullet, but instead the bullet sits in a slot at brace height and the string just snaps it off. This will work- I have tried it with this

- https://thearbalistguild.forumotion.com/t689-paleo-legal-compound#6411 - airgun pellet placed at forward end of bolt track was kicked its width deep sideways into pine board- so speed was decent. String was destroyed after couple dozen shots though.

It is just matter of finding right materials for the striking surfaces.

Geezer wrote:
Then again, how about a discarding-sabot projectile for a bullet-bow? Again, we have lost energy through the sabot, but the internal dart could be a hum-dinger! 

We could allways loose the sabot and mount the dart straight against string.
Darts are quite commonly used with crossbows. I believe professionals call them "bolts" .

Here is interesting solution to the problem by member Fiddler
http://paleoplanet69529.yuku.com/topic/59648/Hickory-board-cross-bow-tested-my-ball-rock-shooting-arrow

He uses cup pointed arrow as a sabot .