Does anyone use anything to "lube" the bolt track? Use silicone on the track or a wax on the bolt to reduce friction? Or would such a thing wear off too quickly to actually help. Or worse attract dust and grit.
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+6
Pavise
Regerald
basileus
Geezer
Lightly
Basilisk120
10 posters
Greasing the track
Basilisk120- Moderator
- Posts : 548
Join date : 2010-03-01
Age : 45
Location : Arizona
- Post n°1
Greasing the track
Just thought I would throw this out to the group.
Does anyone use anything to "lube" the bolt track? Use silicone on the track or a wax on the bolt to reduce friction? Or would such a thing wear off too quickly to actually help. Or worse attract dust and grit.
Does anyone use anything to "lube" the bolt track? Use silicone on the track or a wax on the bolt to reduce friction? Or would such a thing wear off too quickly to actually help. Or worse attract dust and grit.
Lightly- Master Crossbowyer
- Posts : 199
Join date : 2010-01-12
Age : 64
Location : Austin, Tx
- Post n°2
Re: Greasing the track
Couldn't sleep?!
This is a good question...
According to Geezer, the bolts are quicker when we use a micarta or bone groove rather than just the groove in wood, the former being 'more slick'... he has also mentioned that a groove that is well finished with the Tung Oil or maybe lacquer? may also be a bit faster.
If the grooves are anything like bicycle chains (yeah, not so much...) than anything that attracts dust WILL cause drag (I used to be a bicycle mechanic/instructor of classes re rebuilding all hubs, bottom brackets, headsets before they were all one piece that gets pressed in...) so if one DID use a lube; silicone before something else, likely.
But, Geezer will know this better.
Best!
Lightly
This is a good question...
According to Geezer, the bolts are quicker when we use a micarta or bone groove rather than just the groove in wood, the former being 'more slick'... he has also mentioned that a groove that is well finished with the Tung Oil or maybe lacquer? may also be a bit faster.
If the grooves are anything like bicycle chains (yeah, not so much...) than anything that attracts dust WILL cause drag (I used to be a bicycle mechanic/instructor of classes re rebuilding all hubs, bottom brackets, headsets before they were all one piece that gets pressed in...) so if one DID use a lube; silicone before something else, likely.
But, Geezer will know this better.
Best!
Lightly
Geezer- Master Crossbowyer
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- Post n°3
greasing the track
Geezer here: As Lightly said, in my experience, it helps immensely if you have a hard, slick track to begin with. Years ago, a fellow crossbow maker replaced the wooden self-groove in his 125 lb (Alchem prod) medieval-style crossbow with a Delrin one, then reassembled everything exactly as before. The unmodified bow was getting 195 fps with his target bolts (11/32nd Cedar shafts, about 15 inches long, with 125 grain heads, as I recall). The new track gave him 215fps with the same bolts. That's a 20 fps improvement, or just over 10% increase in velocity which showed up clearly on the target range. So a slick top will definitely improve things.
Lubrication should help even more. Beeswax is pretty sticky, and will attract foreign-material. It may help prolong string-life, but probably won't help velocity. Some people use graphite, which works well, but it will leave a dark residue atop the stock, on bowstring and bolts. I recommend silicone, which dries clear and leaves no residue. Try it, you'll like it. Geezer
Lubrication should help even more. Beeswax is pretty sticky, and will attract foreign-material. It may help prolong string-life, but probably won't help velocity. Some people use graphite, which works well, but it will leave a dark residue atop the stock, on bowstring and bolts. I recommend silicone, which dries clear and leaves no residue. Try it, you'll like it. Geezer
Basilisk120- Moderator
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- Post n°4
Re: Greasing the track
Makes sense. I was playing around with some different things I had lying around the house trying to find some way to reduce friction of wood to wood contact. And well to sum it up: A good smooth polyurathane finish is hard to beat. Granted I don't have anything cool like a chronograph to measure speed so it was just a rough 'feel' test.
i will have to try Silicon, I don't have any at home and to be honest I didn't even think about it till I wrote it down in the first post.
i will have to try Silicon, I don't have any at home and to be honest I didn't even think about it till I wrote it down in the first post.
basileus- Crossbow Building Wiki
Founder & Curator - Posts : 86
Join date : 2010-06-18
- Post n°5
Re: Greasing the track
This 10% increase in speed interests me . My crossbows have wooden bolt tracks which are treated with linseed oil followed by beeswax. That kind of surface is really sticky, especially until beeswax is dry. However, my bowstrings only barely touch the top of the stock even before being draw. So the only source of friction is the bolt itself.
Would I still benefit significantly from making the bolt track from metal or ivory?
Would I still benefit significantly from making the bolt track from metal or ivory?
Lightly- Master Crossbowyer
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- Post n°6
Re: Greasing the track
Yes.
Take a look at this:
http://www.flickr.com/photos/swifthoundbows/4012783743/in/set-72157622262033595/
This is a maximilian bow, and the bolt groove inlet is of micarta, and that will be faster than wood. However, Geezer says, that bone or especially Delrin, (which is slick) will be even faster; it was the Delrin inlay that his friend installed that gave that 10% increase...
This photo shows the inset more clearly, at the tip of the bow.
http://www.flickr.com/photos/swifthoundbows/3998209017/in/set-72157622262033595/
Take a look at this:
http://www.flickr.com/photos/swifthoundbows/4012783743/in/set-72157622262033595/
This is a maximilian bow, and the bolt groove inlet is of micarta, and that will be faster than wood. However, Geezer says, that bone or especially Delrin, (which is slick) will be even faster; it was the Delrin inlay that his friend installed that gave that 10% increase...
This photo shows the inset more clearly, at the tip of the bow.
http://www.flickr.com/photos/swifthoundbows/3998209017/in/set-72157622262033595/
Regerald- Master Crossbowyer
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Join date : 2009-11-30
Age : 38
Location : Finland
- Post n°7
Re: Greasing the track
I don't believe that bolt itself cause any significant friction.. Only string, which is usually strongly pushed against stock in medieval type of crossbow. My argument - simple physics. If nothing is pushing bolt against it's groove, friction is caused by it's own weight. Friction constant (wood/wood) is about 0.25-0.5, so energy loss can be easily calculated. For a steel crossbow that basileus has, I've got about 0.15 Joules of energy lost by bolt friction. Which is insignificant, I think..
If something is pushing down a bolt during it's acceleration, problem isn't in a friction.. I think that can be checked correct stiffness of a string or something else..
Am I correct or is there any other facts that affect a bolt friction?
If something is pushing down a bolt during it's acceleration, problem isn't in a friction.. I think that can be checked correct stiffness of a string or something else..
Am I correct or is there any other facts that affect a bolt friction?
Basilisk120- Moderator
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- Post n°8
Re: Greasing the track
Pesky, pesky friction. The bane of simple dynamic equations everywhere.
The coefficent of friction that you posted Regerald is technically the coefficient of static friction. Coefficents of dynamic friction are generally lower so that gives us a decent upper bound. I was supprised that they were as low as they were.
For those that are interested a quick friction primer:
http://en.wikipedia.org/wiki/Friction#cite_note-engHandbook-6
Friction force = Mu * Fn; Were Mu is the coefficient of friction and Fn is the
Normal Force
This also means that contact area is irrelavant with reguards to friction force. Though Total work lost to friction depends on the distance traveled.
Coefficients of friction are all experimentally determined and, unfortunalty, change with a great number of variables including speed. At high velocies the coefficent of friction decreases.
All that said. Did some quick math based on the work done by friction and found at worst a 5.6 ft/sec drop in speed from friction (assuming a constant wood to wood coeffient of friction of .5 and a 1 foot track)
I could see the string loosing more to friction as it could have a higher normal force due to it pulling down on the track. and a possible higher coefficent of friction so anything that would lower help with that could be more useful.
So basically all that to say that experimental results are more reliable than quick mathmatical models. expecially with so many variables like surface finishes, fletching drag, string contact force and high speeds. and friction is a complex area of study.
The coefficent of friction that you posted Regerald is technically the coefficient of static friction. Coefficents of dynamic friction are generally lower so that gives us a decent upper bound. I was supprised that they were as low as they were.
For those that are interested a quick friction primer:
http://en.wikipedia.org/wiki/Friction#cite_note-engHandbook-6
Friction force = Mu * Fn; Were Mu is the coefficient of friction and Fn is the
Normal Force
This also means that contact area is irrelavant with reguards to friction force. Though Total work lost to friction depends on the distance traveled.
Coefficients of friction are all experimentally determined and, unfortunalty, change with a great number of variables including speed. At high velocies the coefficent of friction decreases.
All that said. Did some quick math based on the work done by friction and found at worst a 5.6 ft/sec drop in speed from friction (assuming a constant wood to wood coeffient of friction of .5 and a 1 foot track)
I could see the string loosing more to friction as it could have a higher normal force due to it pulling down on the track. and a possible higher coefficent of friction so anything that would lower help with that could be more useful.
So basically all that to say that experimental results are more reliable than quick mathmatical models. expecially with so many variables like surface finishes, fletching drag, string contact force and high speeds. and friction is a complex area of study.
Basilisk120- Moderator
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- Post n°9
Re: Greasing the track
I was trying to figure out how much velocity would be lost due to the slightly lower acceleration due to friction but that was not as simple as string drag would play a decent part of that.
I could see that adding up to a 15 to 20 ft/sec drop itself.
I could see that adding up to a 15 to 20 ft/sec drop itself.
Pavise- Dear Friend, You will be Greatly Missed.
- Posts : 128
Join date : 2010-02-07
- Post n°10
Re: Greasing the track
Wow! The things one learns on this 'site eh. Simply amazing.
Robin always said that one should be just able to lift the string from the deck with one's little finger when in the unspanned position. Any more effort needed than this means that you'll have too much friction. And friction means heat. So be considerate about what you use for a barrel (plastics) and serving material on the string, as well as the "lube".
Pavise
Robin always said that one should be just able to lift the string from the deck with one's little finger when in the unspanned position. Any more effort needed than this means that you'll have too much friction. And friction means heat. So be considerate about what you use for a barrel (plastics) and serving material on the string, as well as the "lube".
Pavise
Lightly- Master Crossbowyer
- Posts : 199
Join date : 2010-01-12
Age : 64
Location : Austin, Tx
- Post n°11
Re: Greasing the track
Pavise, that is terrific advice that I will keep in mind... I just had to spend some good amount of time fixing a client bow that had too much string drag. I had improperly calculated the angle of the prod. Or rather, the prod socket. Lucky for me, the prod was attached by bow irons, so, I did not have to cut the prod off and re tie it back on two or three times... I corrected the angle, finally...
Thank you!
Lightly
Thank you!
Lightly
Regerald- Master Crossbowyer
- Posts : 67
Join date : 2009-11-30
Age : 38
Location : Finland
- Post n°12
Re: Greasing the track
That doesn't matter. Even if we have a friction constant as large as 2 or 3, energy loss still remains insignificant. And, at last, coefficients for dynamic friction (sliding in this case) are always smaller than for a static friction. I took the largest as "worst case scenario"basilisk120 wrote:
The coefficent of friction that you posted Regerald is technically the coefficient of static friction. Coefficents of dynamic friction are generally lower so that gives us a decent upper bound. I was supprised that they were as low as they were.
Can you expose this math? 5.6 ft/sec drop at which initial velocity? Velocity dependence of bolt's kinetic energy isn't linear, so velocity drop strongly depends of an initial velocity, while the energy drop can be assumed (more or less) constant. In my case: work done by a friction W = C*m*g*s, where weight of a bolt m*g is this "normal force" (if you shoot horizontally). By substitution of a values for one fit draw length, 50gramm bolts (0.05kg in CI), friction constant "C" ,say, 0.5, we getbasilisk120 wrote:
All that said. Did some quick math based on the work done by friction and found at worst a 5.6 ft/sec drop in speed from friction (assuming a constant wood to wood coeffient of friction of .5 and a 1 foot track)
0,5*0,05(kg)*9,81(m/s^2)*0,3048(m) = 0,074 Joules. At initial velocity 50m/s this energy loss corresponds to velocity loss of ~0.03 m/s or near 0.1 fps
If something isn't possible even in theory - even for any possible values of variables - there is no need for a practical experiment. Otherwise you'll find yourself constructing a perpetual.. out of bolts with a huge frictionbasilisk120 wrote:
So basically all that to say that experimental results are more reliable than quick mathmatical models. expecially with so many variables like surface finishes, fletching drag, string contact force and high speeds. and friction is a complex area of study.
But, a practical think: one can put some pigment on a bolt (like pencil graphite), and check, does it even leave the trace on a groove (does bolt even touch the groove, or is it "lifted" by acceleration)..
Pavise- Dear Friend, You will be Greatly Missed.
- Posts : 128
Join date : 2010-02-07
- Post n°13
Re: Greasing the track
Wow!
Now I wonder why Robin Allen never talked about all this mathematical theory.
But he was a practical man and could truly shoot well with any of his crossbows.
And I'm honoured to be able to pass along what I learned from him; especially to you Lightly.
Pavise
Now I wonder why Robin Allen never talked about all this mathematical theory.
But he was a practical man and could truly shoot well with any of his crossbows.
And I'm honoured to be able to pass along what I learned from him; especially to you Lightly.
Pavise
Basilisk120- Moderator
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Location : Arizona
- Post n°14
Re: Greasing the track
Regerald wrote:
But, a practical think: one can put some pigment on a bolt (like pencil graphite), and check, does it even leave the trace on a groove (does bolt even touch the groove, or is it "lifted" by acceleration)..
I unintentionally did that. My first set of bolts were painted red and they left a strip of paint on the top plate. Though when I switched to a new set of arrows with different fletching the new bolts left a paint mark in a different place. i should add my crossbow has a ramp on the front ent with the track in it so the bolt only touching in a small area makes sense as compared to a bow with a full length track
So here is the math I was using. Maybe a case of me trying to be too clever.
(Reginald just spelling it out so it obvious and I'll rember how I did it next time I read this topic)
W= F * x (Work = force * Distance)
W = .5*m*(v2^2 - v1^2) (Work = delta E or E2-E1)
F= C *Fn (Force = friction coefficent * Normal Force )
Fn = m*g (Normal Force = mass * gravity - assuming same assumtion about bolt being horizontal or close enough)
so
W=W
C*m*g*x = .5*m*(v2^2-V1^2) were V1 is the intial velocity so it is 0 and masses cancel
2*C*g*x=v2^2
sqrt(2*C*g*x)=v2
assuming C = .5 g =9.81m/s^s x=.3048m (1 foot) v2 = 1.73 m/s
hence slowing by 1.73 m/s
This was making the assumtion that friction was doing work for the entire distance. It was not as the paint marks will attest and only the rear of the bolt will travel the entire track.
Well geezer put some results from testing that showed that changeing the tarack material resulted in a decent jump in speed. Though you are right that it appears that unless something else is going on then most of that speed jump is from something other than just bolt friction.
Pavise- Dear Friend, You will be Greatly Missed.
- Posts : 128
Join date : 2010-02-07
- Post n°15
Re: Greasing the track
Does anyone have plans for a cheap wind tunnel?
Pavise
Pavise
Basilisk120- Moderator
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Location : Arizona
- Post n°16
Re: Greasing the track
Here are some from NASA: http://www.grc.nasa.gov/WWW/k-12/WindTunnel/build.html
Seems like something that should be realativly easy in theory to do. As long at its a sub sonic wind tunnel, making a supersonic wind tunnel would take more work as the compressablity of air makes it tricky.
Seems like something that should be realativly easy in theory to do. As long at its a sub sonic wind tunnel, making a supersonic wind tunnel would take more work as the compressablity of air makes it tricky.
Pavise- Dear Friend, You will be Greatly Missed.
- Posts : 128
Join date : 2010-02-07
- Post n°17
Re: Greasing the track
Thank you basilisk. I will probably build such a wind tunnel to test my theory about aerodynamic losses due to poor limb design.
Now as for frictional losses due to the bolts contact with the barrel, there are some basics to consider. No matter what we do: the bolt will bend before it starts to move! (See any high speed video of this to verify.) It is the resulting slight wobble from side to side and up and down that leaves the varying and incomplete signatures we see from painted or crested bolts etc. The slot width should be made with a certain bolt in mind and again the late Robin Allen covers this well on his website, under Track Dimensions I believe it is. And it is well to note that dedicated target crossbows invariably have very long tracks or barrels. This is in order to stabilize the shaft for as long as is practical and thus improve intended accuracy; not unlike a long gun barrel in effect. Delrin is a good material but UHMW is even better as far as coefficient of friction is concerned, but it requires special techniques and adhesives to fasten it to wooden stocks. None of this is new. Crossbow makers were doing it years ago and had to work with what they had available for the most part. And as dear Robin always used to say, "Try it mate and see if it works. That's how we learn!" God, how I miss my friend.
Pavise
Now as for frictional losses due to the bolts contact with the barrel, there are some basics to consider. No matter what we do: the bolt will bend before it starts to move! (See any high speed video of this to verify.) It is the resulting slight wobble from side to side and up and down that leaves the varying and incomplete signatures we see from painted or crested bolts etc. The slot width should be made with a certain bolt in mind and again the late Robin Allen covers this well on his website, under Track Dimensions I believe it is. And it is well to note that dedicated target crossbows invariably have very long tracks or barrels. This is in order to stabilize the shaft for as long as is practical and thus improve intended accuracy; not unlike a long gun barrel in effect. Delrin is a good material but UHMW is even better as far as coefficient of friction is concerned, but it requires special techniques and adhesives to fasten it to wooden stocks. None of this is new. Crossbow makers were doing it years ago and had to work with what they had available for the most part. And as dear Robin always used to say, "Try it mate and see if it works. That's how we learn!" God, how I miss my friend.
Pavise
Last edited by Pavise on Fri Aug 27, 2010 2:15 pm; edited 1 time in total (Reason for editing : Typo)
Lightly- Master Crossbowyer
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- Post n°18
Re: Greasing the track
Pavise, I looked up UHMW material, and it looks interesting...
You mention special adhesives for that material, do you know which? We use Gorilla Glue for the micarta (in addition to pinning it) for when we use it for a bolt groove inset. And, scratch it up, to help it grab.
In your opinion, (altho not traditional, of course!) would it be worth trying some of the UHMW stuff for bolt grooves, like we use the micarta? For personal bows...
We use the micarta on client bows as it somewhat resembles bone, and even, has a tendency to 'yellow' with age, like bone...
Thanks!
Lightly
You mention special adhesives for that material, do you know which? We use Gorilla Glue for the micarta (in addition to pinning it) for when we use it for a bolt groove inset. And, scratch it up, to help it grab.
In your opinion, (altho not traditional, of course!) would it be worth trying some of the UHMW stuff for bolt grooves, like we use the micarta? For personal bows...
We use the micarta on client bows as it somewhat resembles bone, and even, has a tendency to 'yellow' with age, like bone...
Thanks!
Lightly
Thee Apprentice- Fresh Blood
Doesn't mean
I'm new to crossbows - Posts : 4
Join date : 2010-08-23
Age : 48
Location : Oregon
- Post n°19
Re: Greasing the track
Why not go all out for performance and put a PTFE/Teflon track in place? Its white typically and tends to be very soft and easy to machine. Not sure how well you could glue it in because its so slick but you could probably pin it.
http://www.mcmaster.com/#plastics/=8l7qc6
http://www.mcmaster.com/#plastics/=8l7qc6
Pavise- Dear Friend, You will be Greatly Missed.
- Posts : 128
Join date : 2010-02-07
- Post n°20
Re: Greasing the track
Hello Lightly,
If you Google "gluing UHMW" you will find several answers, but I always use G2 epoxy and flame heat the surface (3 sides) of the plastic insert first. I also provide strategically placed recesses in the plastic where a mechanical bond will be generated as the epoxy sets and adheres to the more accepting wood. Again, I learned this from Robin who himself learned it from the Samurai. Some say that Loctite 401 in combination with their 770 Primer works well for this application too. I see no reason, other than what you have raised, why UHMW would not work for common bolt grooves except that it is vulnerable to accidental impact damage despite its extreme resistance to wear. As well as being easily chiselled and planed, UHMW may be machined and shaped with router bits and end mills but is almost impossible to sand without overheating and spoiling the desired finish.
Kind regards,
Pavise
If you Google "gluing UHMW" you will find several answers, but I always use G2 epoxy and flame heat the surface (3 sides) of the plastic insert first. I also provide strategically placed recesses in the plastic where a mechanical bond will be generated as the epoxy sets and adheres to the more accepting wood. Again, I learned this from Robin who himself learned it from the Samurai. Some say that Loctite 401 in combination with their 770 Primer works well for this application too. I see no reason, other than what you have raised, why UHMW would not work for common bolt grooves except that it is vulnerable to accidental impact damage despite its extreme resistance to wear. As well as being easily chiselled and planed, UHMW may be machined and shaped with router bits and end mills but is almost impossible to sand without overheating and spoiling the desired finish.
Kind regards,
Pavise
Basilisk120- Moderator
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- Post n°21
Re: Greasing the track
Pavise wrote:Thank you basilisk. I will probably build such a wind tunnel to test my theory about aerodynamic losses due to poor limb design.
Now as for frictional losses due to the bolts contact with the barrel, there are some basics to consider. No matter what we do: the bolt will bend before it starts to move! (See any high speed video of this to verify.) It is the resulting slight wobble from side to side and up and down that leaves the varying and incomplete signatures we see from painted or crested bolts etc. The slot width should be made with a certain bolt in mind and again the late Robin Allen covers this well on his website, under Track Dimensions I believe it is. And it is well to note that dedicated target crossbows invariably have very long tracks or barrels. This is in order to stabilize the shaft for as long as is practical and thus improve intended accuracy; not unlike a long gun barrel in effect. Delrin is a good material but UHMW is even better as far as coefficient of friction is concerned, but it requires special techniques and adhesives to fasten it to wooden stocks. None of this is new. Crossbow makers were doing it years ago and had to work with what they had available for the most part. And as dear Robin always used to say, "Try it mate and see if it works. That's how we learn!" God, how I miss my friend.
Pavise
You must have read my mind Pavise. I was just wondering about the bolt flexing. I was just looking at the paint marks on my bow and noticed that the tail end of the bolt is what is dragging and leaving paint. It also takes a bit of force and speed to leave that much paint. So it does look like the normal force on the bolt is greater than merely the weigh of the bolt.
Three Apprentice:
I noticed that McMaster Carr has sticky back PTFE film. Hmm wonder how that stuff would hold up to repeated use on a crossbow .
Basilisk120- Moderator
- Posts : 548
Join date : 2010-03-01
Age : 45
Location : Arizona
- Post n°22
Re: Greasing the track
I ordered some of the sticky backed PTFE film to try on my crossbow. I figured it can't do anything to the bow that I can't fix Besides if all else fails I have a new crossbow on order with New World Arbalist Soo can't wait.
But I'll let everyone here know how it turns out and how it takes to repeated abuse.
But I'll let everyone here know how it turns out and how it takes to repeated abuse.
Pavise- Dear Friend, You will be Greatly Missed.
- Posts : 128
Join date : 2010-02-07
- Post n°23
Re: Greasing the track
Don't forget to patent and register your findings too.
Pavise
Pavise
Lightly- Master Crossbowyer
- Posts : 199
Join date : 2010-01-12
Age : 64
Location : Austin, Tx
- Post n°24
Re: Greasing the track
Wait! You DO?! Which one?! Just want to see if *I* have that order!
(At Basilisk!)
Best!
Lightly
(At Basilisk!)
Best!
Lightly
Basilisk120- Moderator
- Posts : 548
Join date : 2010-03-01
Age : 45
Location : Arizona
- Post n°25
Re: Greasing the track
Lightly
Walnut Maximillian with steel prod, bow irons and micarta track. Its going to be my Christmas present. My wife was threatening that when it arrives she was going to wrap it up and make me wait till Christmas to open it.
Walnut Maximillian with steel prod, bow irons and micarta track. Its going to be my Christmas present. My wife was threatening that when it arrives she was going to wrap it up and make me wait till Christmas to open it.