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a new type of wadding?

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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a new type of wadding?

Unread postAuthor: rathunter » Wed May 28, 2014 7:59 pm

So I was messing around with lead wheel weights and potato guns. Not a good combo, my gun (1.5" bore) can put a lead wheel weight through 1/2 inch of plywood(i meant that it was dangerous...). I just spray some propane slightly upside down, and it makes a mist. when I can see the base of the ammo I screw the cap on. Point at me target and pull the trigger. Any more than 1/2 potato makes my hand hurt a bit.
Basically I was going through too many potatoes. Potatoes are a bit... expensive.
So I came up with a (maybe) new ammo: use wet paper towels for wadding. They are cheap... and REUSEABLE.
Also the make an AMAZING seal, and the water lubricates the barrel. Propane is so clean burning it it doesn't gum the barrel. I suppose you guys already know that.

Well, if you are an airsofter like me, take 1 wad of wet paper towel, shove down barrel, pour ~3" of .12g BB's down the barrel, then a DRY paper towel wad. It will literally blow a 10" hole into a cardboard box(one side) at 10 feet.
Also you can use wet paper towel wads for just about ANYTHING that requires wadding. they are VERY cheap.
Wet newspaper works almost as well but has a tad bit more barrel friction and is harder to soak.
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Last edited by rathunter on Thu May 29, 2014 6:16 pm, edited 1 time in total.

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Re: a new type of wadding?

Unread postAuthor: jackssmirkingrevenge » Thu May 29, 2014 1:24 pm

When the burning gas meets the water, it cools, reducing pressure and therefore power.

Personally I would take you concept a little further, wet the towel, jam it into a length of PVC pipe the same as your barrel, let it dry and then use it as a wad.
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Re: a new type of wadding?

Unread postAuthor: rathunter » Thu May 29, 2014 6:13 pm

Really, that isn't much of an issue. What about the water content of a potato?
I see your point, but I have noticed that wet paper towels go much, much, much further than dry paper towels. Much better seal.
Here is why I don't think it is an issue:
1. Wet goes further than multiple dry
2. when I put a ~2 oz spud in the barrel it goes pretty far.
3. when I put a 1/2 oz wet paper towel in+ an apple core it goes signifigantly farther, depending on how good my propane/air mix is.
4. it is much louder with a wet paper towel VS a potato: better sealing, plus some of the water evaporating generates more pressure(remember, when water turns to steam it expands almost 100x depending on temp). There are several reasons there were water injectors on some WW2 aircraft- it generates more power. I think this more than overcomes the slight cooling of the gasses.
Also, the slightly higher friction of a wet paper towel gives more time for the burn to complete.
Let us put it this way- I really like wet paper towels compared to potatoes.
If you carefully roll a handful of wet paper towels into a ball, and cover it with a single dry paper towel(that rapidly gets wet)it will go pretty far before breaking up.
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Re: a new type of wadding?

Unread postAuthor: jackssmirkingrevenge » Fri May 30, 2014 5:03 am

rathunter wrote:There are several reasons there were water injectors on some WW2 aircraft- it generates more power. I think this more than overcomes the slight cooling of the gasses.


Not quite the same, water injection in an engine is there to cool the fuel air mixture and therefore increase its density, meaning more fuel and air can be pumped in the same volume, in the same way intercoolers function. It also prevents premature ignition due to compression and therefore reduces knocking.

some of the water evaporating generates more pressure(remember, when water turns to steam it expands almost 100x depending on temp).


This might be true in the high temperature and pressure environment of an internal combustion engine, but I can guarantee it's not happening in your potato gun ;)

Also, the slightly higher friction of a wet paper towel gives more time for the burn to complete.


You would think wet slides easier than dry hehe

Let us put it this way- I really like wet paper towels compared to potatoes.


Noted. I will quote my current favourite show, "gubba nub nub du rocka" :D

It would be cool to see some video comparison of wet vs dry so we can judge the difference for ourselves if you have the time and inclination.
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Re: a new type of wadding?

Unread postAuthor: Ragnarok » Fri May 30, 2014 8:38 am

rathunter wrote:I see your point, but I have noticed that wet paper towels go much, much, much further than dry paper towels. Much better seal.

That's an aerodynamics issue (and very little to do with the seal). Wet paper towels are a congealed lump with mass, instead of the lightweight sail that dry paper towels are.

remember, when water turns to steam it expands almost 100x depending on temp

Definitely a net loss.

Boiling a single cubic centimetre of water from 20 Celsius takes nearly 2600 Joules. Now, in theory that expands to 1700cc of steam (water has a density of ~1kg per litre at 20C, steam at 100C is ~0.6 grams per litre), but it took the energy of (assuming perfect and instant heat transfer) 670cc of Propane-Air mix to do.
670cc of Propane-Air mix would instead normally expand to somewhere about 5000cc, about three times the volume of the steam.

There's some circumstances in which it works (mostly those where the fuel-air mixture needs to be cooled to increase its density), but this is not one of them.
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Re: a new type of wadding?

Unread postAuthor: Brian the brain » Fri May 30, 2014 2:55 pm

Would injecting watervapor at high temperature ( close to boiling) just prior to ignition work??
Just wondering...
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Re: a new type of wadding?

Unread postAuthor: Ragnarok » Sat May 31, 2014 4:31 pm

Brian the brain wrote:Would injecting watervapor at high temperature ( close to boiling) just prior to ignition work??
Just wondering...

Hot water would make little difference.

A calorie is how much energy it takes to heat a gram of water by one Celsius, so heating water from room temperature to boiling point takes about 75-80 calories per gram. It takes 540 calories to convert one gram of liquid water at 100C to gaseous water at 100C.
This is why pans of water don't suddenly reach boiling point and suddenly go "whoompf", completely turning into steam in an instant.

There is a marginally similar effect that could be worth investigating, which is helium as a buffer gas.
The thing about helium is that it's a very low density gas. Adding it on top of a fuel mix shouldn't significantly increase the mass in the chamber, so in turn shouldn't much reduce the temperature (and pressure) post combustion, but does drastically lower the density.
Lower density fluids have a lower kinetic energy at any given velocity, meaning that at high velocities the dynamic pressure remains higher (see the Bernoulli equation), and in theory so does the projectile acceleration - even in spite of a lowered peak pressure.

However, we are talking about serious velocities where this would start to come into play, and only hybrids could possibly capitalise on such an effect.
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Re: a new type of wadding?

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Re: a new type of wadding?

Unread postAuthor: rathunter » Sat May 31, 2014 11:11 pm

I realize your point. But I'm theorizing on why a wet wad pushes lead weights out of the barrel much faster than dry. They aren't equel weight, the wet is heavier, so it should go slower.
Here is the differences-
the wet is MUCH harder to push down the barrel(I usually just pound it in a few inches, then put the loading stick slightly in the ground, then ram the cannon on top. Else it takes several mins just to get it down the bore.
Once you get the wet moving, it is a LOT easier than it was to get it moving.
the wet has a MUCH better seal for a given bit of paper.
the wet doesn't catch on fire(yes, that is a problem).
the wet shoots harder. Lead wheel weights go a lot farther with wet than dry paper towels.
Water injection on some aircraft engines was actually to boost power- and it wasn't always due to increased fuel density.
the water injection system made the fuel-air mix leaner. then added water in the carburetor. This did slightly cool down the fuel, but the MAIN benefit was the water droplets would reduce peak cylinder temp and their vaporization increased power significantly. Enough to allow an overloaded bomber to take off on a short runway.
However, if I were to spray a fine mist of water into the combustion chamber, I doubt it would have much benefit because the peak temperature is pretty low.
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Re: a new type of wadding?

Unread postAuthor: Ragnarok » Sun Jun 01, 2014 6:14 pm

rathunter wrote:I realize your point. But I'm theorizing on why a wet wad pushes lead weights out of the barrel much faster than dry.

I'll admit to some poor phrasing on my part before.

I'm not doubting that a wet paper towel will seal better and certainly a good seal is important to muzzle velocity - but when talking about how far something flies, such a huge difference in ballistic coefficient (probably a factor in the tens or hundreds) is a far more significant factor than how much the seal might have improved the muzzle velocity (probably a factor of less than two).
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Re: a new type of wadding?

Unread postAuthor: jimmy101 » Tue Jun 03, 2014 3:52 pm

It has nothing to do with vaporizing the water, or water injection or anything like that.

All the wet is doing is letting you pack the wading much tighter and that is giving higher static friction between the barrel and ammo. Higher static friction is, in a combustion gun, paradoxically better than lower static friction. Indeed that is why a double-beveled spud cutter works better than a single outer bevel.

Combustion is a pretty slow process. So slow that with a low friction ammo the ammo will exit the barrel long before combustion is complete. By increasing the static friction you let combustion proceed farther, and the pressure to rise more, before the ammo starts to move.

By the description of how hard it is to ram home the ammo the static friction has been boosted by a fair amount and that is why the ammo flies farther.

As to how far the wading flies, Ragnarok hit the high point. Try to throw a piper towel. Then soak it in water and wad it up and throw it. There's a reason why there is spit in a spit-ball.

BTW HGDT will model the effects of high versus low static friction. Light ammo is particularly sensitive to the level of static friction, whereas massive ammos are less so.
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Re: a new type of wadding?

Unread postAuthor: mobile chernobyl » Tue Jun 03, 2014 5:40 pm

jimmy101 wrote:It has nothing to do with vaporizing the water...


Very nice summary! It's very easy to look too deeply into a topic and ignore the larger picture.
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Re: a new type of wadding?

Unread postAuthor: dart guy » Wed Jul 23, 2014 10:24 pm

I have designed an almost shot gun like wad for a 2" bore, I took a paper towel Rolland 4 peices of corrugated cardboard and I cut a one inch cylinder from the towel roll and then I made a 2 disks that would fit inside it one for each end, then I cut 2 bore sized disks one for over the bottom and another to be modified, after that I cut out a hole in the middle of the 1 bore sized circle that would fit around the tube section (sometimes I used 2 circles and glued them together for a thicker ring). At this point I would glue together the tube to the tube fitting peices and the bore fitting circle to the one end of the hollow cylinder and at the other end I glued the ring to the top so that it was 1/2 of the way over the top. Now depending on the amount of ammo, I would cut the towel roll 1/2" above the fill point and then cut 3-6 slits down to 1/2" of the bottom then I would some times glue a paper towel over top of the tube to hold the ammo. When fired the air pressure would rupture the towel, expand the slit tube, and fling the load and the wad would slow down. Those where one time use, but if you filled the cylinder with crumpled paper it would make the bottom re useable.
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