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    Bullet bow with a rifled barrel - Discussion & Project planing

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    Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Ivo on Tue Jan 18, 2011 5:31 pm

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

    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". Laughing

    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. Razz



    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.






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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Geezer on Wed Jan 19, 2011 9:10 am

    Geezer here with comments on rifled bullet-bows. It seems to me that the biggest difficulty with rifled bullet-bows would be to make the projectiles 'take' the rifling, without an excess of friction.
    Back in the 19th century, various gun-makers, like Armstrong and Whitworth, experimented with artillery shells fitted with studs to ride in the rifling. If you could make darts, equipped with thin plastic ribs that would ride in the grooves... or a barrel with pronounced spiral ridges that would fit into a grooved projectile, that might be a reasonable way to proceed. If the projectiles could be cast to shape out of some inexpensive resin, you could probably keep costs fairly low... just thinkin' Geezer

    ********

    Or how about inventing some form of magnetic rifling? If we can get
    mag-lev lift and accelerators, why not a system that imparts spin? Too
    weird? Geezer


    Last edited by Ivo on Sun Jan 23, 2011 12:31 am; edited 1 time in total (Reason for editing : Merging a double post)
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Regerald on Wed Jan 19, 2011 11:56 am

    Interesting idea about the magnets.. But it means that bullets themselves have to be magnetic too, which make some expense. And also, barrel material has to be paramagnetic, better if insulator (pvc tube?)

    How about to use as a bullet shortened vertion of those?

    Could be made of full metal by casting or something..
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Basilisk120 on Wed Jan 19, 2011 12:41 pm

    Hey Ivo, it looks like a decent simple solution. cheers
    Now for some questions:
    1. How are you controlling the cutter depth?
    2. What materials are you looking at for the barrel?
    Couple of ideas:
    for chip removal. Extend the cut where the mounting screws are for the cutters then add a groove in front of the cutters that goes to the extended side cut. Make sense?
    Depending on the barrel material and lenght of the barrel extending the coupler to going more over the barrel might not be a bad idea to prevent bending. Depending on the cutters depth it could put a decent compression load on the barrel which could lead to bending or binding of the cutters shaft.

    I second Geezers comment on projectile selection. I have anouther idea to think about. using some kind of sabot or soft driving bands.
    You might want to make your grooves wide and deep. the bullet in a soft sabot could engage the lands but not have to bottom out on the grooves. For a firearm a tight fit of bullet and barrel is a must but for this a tight fit would be detrimental. Basically think about engaging the lands but not filling the grooves. or just minimize surface contact



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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by kiwijim on Wed Jan 19, 2011 5:55 pm

    Hi Guys, Geezer is right. In order for the projectile to engage the rifling excessive friction is generated.

    Also, as the projectile is usually small, round and heavy, (say a 0.50-0.60 cal. lead round ball ) and is not traveling at particularly quickly its momentum will keep it on track - making it very accurate to the distances such a weapon is useful.

    If you have your heart set on putting some spin on the bullet how about devising some kind rifled choke, like shooters use to spin shotgun slugs. This will keep the friction down and projectile speed up.

    Something else to consider is that the barrel does not need to be round, infact a round barrel would generate the most friction with a round bullet scratch . The barrel could have a square or diamond section. Making a bullet spin in a square barrel without generating excessive friction is an much easier problem to solve. Very Happy

    Regards James

    ********

    Something else to consider is that in order of the bullet to spin around
    it's axis it must overcome the friction between itself and the string. I
    don't think this would be possible without fitting a (cast robbing)
    spinning attachment onto the string. With this in mind, the most
    effective rifling will be placed at the very end on the barrel- like a
    rifled choke


    Last edited by Ivo on Sun Jan 23, 2011 12:29 am; edited 1 time in total (Reason for editing : Merging a double post)
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Pavise on Thu Jan 20, 2011 10:43 am

    Yes, kiwijim is right about the effect of the string-pressure-to-base-of-projectile. But I really wonder why folks don't bother to read the works of others who have gone down this path before and have left a trail that we can easily follow. Again I suggest the "Practical Guide to Manpowered Bullets:" by Richard Middleton. Search Google books for a sample of what this man has discovered and made available to us. According to him, the "rifling" doesn't have to be very agressive at all in order to impart resistance and thus spin to the projectile. But, I am not convinced that the string slots on either side of such a barrel would not have more influence and thus negate any rifling effect. Not unless these slots could be cut in such a fashion as to not interfere with the sides of the moving projectile.
    And welcome to latest member Wendy Allen too.
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Geezer on Thu Jan 20, 2011 10:57 am

    Geezer here on rifled bullet-bows. I agree wholeheartedly that the level of discourse would be raised by actually referring to expert sources, but that isn't the nature of the beast. The gang are having arguing the question, and in a social sense, that's what important here.
    In fact, I abandoned bullet-bows and stonebows years ago, thanks to personal misfortune. I have no intention of revisiting the decision to cease experimentation on bullet-bows. But the guys are having fun, so why not keep the ball rolling? Geezer, the Gadfly.
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Geezer on Thu Jan 20, 2011 10:58 am

    Hmm, I meant to say the gang are having FUN, arguing the question... but perhaps that was obvious anyway. Carry on. Geezer
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Pavise on Thu Jan 20, 2011 12:30 pm

    Geezer wrote:Geezer here on rifled bullet-bows. I agree wholeheartedly that the level of discourse would be raised by actually referring to expert sources, but that isn't the nature of the beast. The gang are having arguing the question, and in a social sense, that's what important here.
    In fact, I abandoned bullet-bows and stonebows years ago, thanks to personal misfortune. I have no intention of revisiting the decision to cease experimentation on bullet-bows. But the guys are having fun, so why not keep the ball rolling? Geezer, the Gadfly.
    It is my understanding that Ivo is wanting to build a bullet shooting crossbow "with a barrel" and I respectfully suggested that if he and others would read and heed what Mr. Middleton has written for guidance then Ivo and perhaps some others would be less likely to learn the hard way!
    Fun is my middle name but I temper that with a degree of respect for those who go or went before me. Thus I will continue to reference your works too.
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Ivo on Sat Jan 22, 2011 7:02 pm

    Looks like...I'm getting my butt kicked here. Anyone have a smoke? Laughing Laughing Laughing


    You guys are reading my mind and I only did a rough jig drawing. I remember once seeing a patent for a "shot bow", a barreled bow or crossbow assembly shooting sabots that opened like a clam and were filled with shot or small darts/nails. ...[now got to get home to finish up the post]

    Geezer wrote:Geezer here with comments on rifled bullet-bows. It
    seems to me that the biggest difficulty with rifled bullet-bows would be
    to make the projectiles 'take' the rifling, without an excess of
    friction.
    Back in the 19th century, various gun-makers, like
    Armstrong and Whitworth, experimented with artillery shells fitted with
    studs to ride in the rifling. If you could make darts, equipped with
    thin plastic ribs that would ride in the grooves... or a barrel with
    pronounced spiral ridges that would fit into a grooved projectile, that
    might be a reasonable way to proceed. If the projectiles could be cast
    to shape out of some inexpensive resin, you could probably keep costs
    fairly low... just thinkin' Geezer

    ********

    Or how about inventing some form of magnetic rifling? If we can get
    mag-lev lift and accelerators, why not a system that imparts spin? Too
    weird? Geezer

    Regerald wrote:Interesting idea about the magnets.. But it means
    that bullets themselves have to be magnetic too, which make some
    expense. And also, barrel material has to be paramagnetic, better if
    insulator (pvc tube?)

    How about to use as a bullet shortened vertion of those?

    Could be made of full metal by casting or something..

    Magnets?...not impossible Smile ......a magnetic arrow rest is already old news on the archery market...a bit pricey, but real non the less.



    the use of a power source other than human muscle power can already be
    seen in commercially manufactured pneumatically spanned crossbows, so it's possible that
    electricity is on it's way too.

    Basilisk120 wrote:Hey Ivo, it looks like a decent simple solution. cheers
    Now for some questions:
    1. How are you controlling the cutter depth?
    2. What materials are you looking at for the barrel?
    Couple of ideas:
    for
    chip removal. Extend the cut where the mounting screws are for the
    cutters then add a groove in front of the cutters that goes to the
    extended side cut. Make sense?
    Depending on the barrel material and
    lenght of the barrel extending the coupler to going more over the barrel
    might not be a bad idea to prevent bending. Depending on the cutters
    depth it could put a decent compression load on the barrel which could
    lead to bending or binding of the cutters shaft.

    I second
    Geezers comment on projectile selection. I have anouther idea to think
    about. using some kind of sabot or soft driving bands.
    You might
    want to make your grooves wide and deep. the bullet in a soft sabot
    could engage the lands but not have to bottom out on the grooves. For a
    firearm a tight fit of bullet and barrel is a must but for this a tight
    fit would be detrimental. Basically think about engaging the lands
    but not filling the grooves. or just minimize surface contact

    Thanks for the good words Basilisk...a few years ago I got a glimpse at a
    similar rifling setup and just now it surfaced in my mind...I can't remember
    how it was completed and/or if it worked at all, so every design detail
    is being reinvented.
    I
    didn't decide on the barrel material yet, but considering the
    application I Didn't the need for a steel barrel...I was leaning towards

    aluminum tubes about 1/2" OD that I've seen at the hardware store
    or a combination of this tube with a composite outer shell(fiberglass)
    and/or a plastic(castable resin) inner lining to cut rifling in.

    Funny, I went picking in the hardware store and it's the same story as with board bows...with bows it's grain run
    out, here it's irregularity in wall thickness/center...4 out of 5 I didn't
    even bother getting the caliper out and same thing with caliper in hand
    4 out of 20 were only marginally acceptable. Finding the more or less
    decent tube was just part of the story...the steel rods I was thinking
    of using for the cutter don't match the ID of the tube by about .7mm
    ....suddenly I remember Tomas Edison's words >>> "To invent,
    you need good imagination and a pile of junk" Razz

    As for the cutter design...I'm ashamed to say...I was just going to wing
    the cutter position and bolt it in place, Just couldn't think of
    anything and left the cutter pressing against the bolts and the inner
    wall of the slot.

    There is a possibility that I will take a steel
    rod, cover it with some sort of insulator, give it a few layers of
    resin, let dry and then make the barrel around it by rolling the resin
    covered rod in fiberglass cloth...then just heat it a bit and slide the
    rod out....then cut the rifling in the resin.Think this might be the
    most accurate match that will eliminate the cutter rod rattle.

    kiwijim wrote:Hi Guys, Geezer is right. In order for the projectile to engage the rifling excessive friction is generated.

    Also,
    as the projectile is usually small, round and heavy, (say a 0.50-0.60
    cal. lead round ball ) and is not traveling at particularly quickly its
    momentum will keep it on track - making it very accurate to the
    distances such a weapon is useful.

    If you have your heart set
    on putting some spin on the bullet how about devising some kind rifled
    choke, like shooters use to spin shotgun slugs. This will keep the
    friction down and projectile speed up.

    Something else to
    consider is that the barrel does not need to be round, infact a round
    barrel would generate the most friction with a round bullet scratch
    . The barrel could have a square or diamond section. Making a bullet
    spin in a square barrel without generating excessive friction is an much
    easier problem to solve. Very Happy

    Regards James

    ********

    Something else to consider is that in order of the bullet to spin around
    it's axis it must overcome the friction between itself and the string. I
    don't think this would be possible without fitting a (cast robbing)
    spinning attachment onto the string. With this in mind, the most
    effective rifling will be placed at the very end on the barrel- like a
    rifled choke

    Pavise wrote:Yes,
    kiwijim is right about the effect of the
    string-pressure-to-base-of-projectile. But I really wonder why folks
    don't bother to read the works of others who have gone down this path
    before and have left a trail that we can easily follow. Again I suggest
    the "Practical Guide to Manpowered Bullets:" by Richard Middleton.
    Search Google books for a sample of what this man has discovered and
    made available to us. According to him, the "rifling" doesn't have to be
    very agressive at all in order to impart resistance and thus spin to
    the projectile. But, I am not convinced that the string slots on either
    side of such a barrel would not have more influence and thus negate any
    rifling effect. Not unless these slots could be cut in such a fashion as
    to not interfere with the sides of the moving projectile.
    And welcome to latest member Wendy Allen too.
    Pavise

    Kiwijim, Pavise, you guys. Smile

    I want to comment, but I'm held in suspense...I have a copy of
    Middleton's book in e-book format...started reading it from the
    middle(one of my countless bad habits), I have to scramble through my
    hard drive and take a look at what the man said about these barrels...I
    really
    do want to build this thing or perhaps even a few...so we'll see if the
    Middle ton can shine some light on it and I will quote what ever I
    can to add to the conversation.

    Also I was thinking about the
    rifling on my own and have to agree with all of you...there is too much
    interference from other grooves, the string, perhaps even the angle at
    which the crossbow is held, so the choke idea is reallylooking
    awesome....Loving it since the ability to shoot the earlier mentioned
    shot filled sabots and when necessary simply snap on a rifled choke for
    bullets...brilliant! That and rifling a choke and rifling a barrel are
    like night and day.
    Again I'll look into the book in hopes of finding something good.

    Geezer wrote:Geezer
    here on rifled bullet-bows. I agree wholeheartedly that the level of
    discourse would be raised by actually referring to expert sources, but
    that isn't the nature of the beast. The gang are having arguing the
    question, and in a social sense, that's what important here.
    In
    fact, I abandoned bullet-bows and stonebows years ago, thanks to
    personal misfortune. I have no intention of revisiting the decision to
    cease experimentation on bullet-bows. But the guys are having fun, so
    why not keep the ball rolling? Geezer, the Gadfly.

    Sorry to hear about your eye Geezer, that really sucks.

    I
    remember talking about these bows a while ago on another forum and when
    we stated talking about shooting shot out of then...a red flag went up
    in my head and despite how cool they look with that pouch bow string
    assembly - I've decided to never (or at least not in the near future)
    try building one of these and took up this project from the maximum
    containment standpoint...plus it's an added challenge since we are
    technically building a low power slug/shot shooter combo while
    attempting to maintain maximum efficiency...I'm too excited to sleep on
    it... Laughing

    Definitely,
    let's keep the ball rolling!...book is good, discussion is good, a
    discussion with book material set as ground = Great! I'll try to grab as
    much as possible from the book and will add a the illustrations of the
    more refined (and hopefully final) design of the rifling jig and a sketch of the rifling profile I've decided on.




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    Rifling machine

    Post by 8fingers on Sat Apr 09, 2011 1:11 am

    One of the Foxfire Books had an article on a homemade rifling machine. A piece of drill rod with a cutter made from a piece of a file, attached to a large diameter wooden rod. Made a paper triangle representing ratio of rifling. Wrap this onto the wooden rod. Cut a groove on the spiral. Wooden frame has pegs that ride in the groove causing it to turn. Rotating handle on end of the wooden rod. Make x number of passes with the cutter, go to next peg until you have cut all the grooves you need. Fresh cutter, finish the rifling. Lap the barrel to smooth out rough or tight spots.
    Considering using discarding sabots available for black powder guns from your local gun shop.
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Ivo on Sat Apr 09, 2011 3:04 am

    I've done some more reading on the subject as Pavise suggested - Man powered bullets book.

    Not much on the good news side regarding the use of rifling in crossbows Neutral ,but there is an interesting bit on the fabrication of the rifling jig Very Happy ...similar to what 8fingers is talking about, only instead of a tooth/cutter it uses a metal saw blade embedded into a dowel rod...I'll get back to it a little later with a picture.
    OHhh...and I found this awesome video online picturing a "traditional" gunsmith rifling a forged barrel the "old way"...and seeing that it's so damn similar to what we came up with here - blows my mind. drunken cheers cheers cheers



    I'd love to post a bit more on my discoveries, but It's late as hell right now and my eyes are probably like a pair of strawberries. drunken Razz


    Ivo




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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Warhammer1 on Mon Apr 11, 2011 2:37 pm

    With inswingers it is easy to get a very acute string angle. It is a simple thing therefore to give it a quarter twist before release on my torsion slingshot shooting either blunts or sharps. I have toyed with a few designs of that nature.
    The rifled barrel design I came up with also has a slot running the length of it through which the string passes. Attached to the string within the barrel (same diameter)is a device to push the arrow out. This device is able to spin. It would be simpler to have the arrow nock against this little device snugly and have the device do the rotating. The arrow would release the same as an archery bow except it is now spinning when released. The amount of twist need not be sigificant, a quarter turn or less would do, so one rotation every seven or eight feet. Would help if fletched to aid this action.
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Warhammer1 on Mon Apr 11, 2011 2:50 pm

    An even easier way is to just offset the string slot near the end of the stroke. Not much, one side one eigth up the other one eigth down. Be hell on the serving tho. Impart twist right at end of stroke to minimize string wear.
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by basileus on Fri Apr 15, 2011 2:36 pm

    Here's an idea... have a barrel cut in two, the bowstring passing through the halves. Attach a two-part "pusher" device to the middle of the bowstring. The outer part of this device would rotate freely, and would be shaped so that when the bowstring starts moving forward, the device starts rotating due to air pressure - and the projectile with it. Of course, the projectile's shape would have to allow air flow to the device.

    Alternatively one could skip the rotation altogether, make the "pusher" magnetic, slightly concave and from one part. It would then automatically center any size of steel ball one throws at it. It could probably take slightly elongated projectiles too, in which case making it from two parts (as above) would allow it to rotate and thus stabilize the projectile. So, in this case the barrel would only serve as a "track" for the device holding the actual projectile. Kind of a pouched bullet crossbow with a single string and a barrel.


    Last edited by basileus on Fri Apr 15, 2011 2:38 pm; edited 1 time in total (Reason for editing : Clarified a few points)

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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by 8fingers on Sun Apr 17, 2011 12:06 pm

    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.
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Ivo on Sun Apr 17, 2011 8:59 pm

    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. scratch Hmmm...very cool stuff! bom

    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:

    "Tear drop" is a component known in archery that is used to connect the cable to bowstring in compound bows. There is two different tear drops that I know of...one is a solid part of the cable -singe tear drop

    ...and the double sided tear drop - a separate component to which the cable and bowstring connect independently.

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


    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. Smile


    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. Smile



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

    Regards,

    Ivo




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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by vabowyer on Tue Apr 19, 2011 6:19 pm

    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.
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Ivo on Wed Apr 20, 2011 10:47 pm

    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.
    Laughing

    Spoiler:




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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by mac on Thu Apr 21, 2011 7:31 am

    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

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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by 8fingers on Thu Apr 21, 2011 8:54 am

    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.
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Ivo on Fri Apr 22, 2011 8:31 pm

    Where would I be without you guys. cheers


    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? Smile

    Ivo


    Last edited by Ivo on Sat Apr 23, 2011 7:14 pm; edited 2 times in total




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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by mac on Fri Apr 22, 2011 10:43 pm

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

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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by 8fingers on Sat Apr 23, 2011 10:43 pm

    My sons play paint ball and use hop up barrels. By rotating their weapons horizontally, they can shoot around corners. Twisted Evil
    Anybody up for some trick shooting? flame thrower
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    Re: Bullet bow with a rifled barrel - Discussion & Project planing

    Post by Ivo on Tue May 31, 2011 3:21 am

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

    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 Mad, 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. Laughing

    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 scratch ...any thoughts?

    Ivo




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