Touch hole location-----just have to know why

[hhughh]

Before I start this, let me say: This is NOT bragging, boasting, or anything of the sort. I am well aware that it is purely luck that caused this, but I'd like to know the technical details behind the "luck", so I can continue to duplicate this.

I built a Tn/Southern style flinter in the summer of '96. I've built a couple of "kit guns" in the meantime--a GPR, etc--and have just completed a NE Fowler from Chambers.

What I have to ask about is touchhole location. On that first rifle, there are more mistakes than I care to talk about, and I simply "good-eyed" the touchhole, and drilled it with a drill press. I never installed a TH Liner.

(Now, I'm going to knock on wood, and please remember what I said at the beginning.) In ten or so years, I have had one flash in the pan. I occassionally try a flint one shot too long, and it doesn't draw enough sparks to touch off the powder, but if the priming ignites, the gun goes off.

On the new fowler, I basically attempted to duplicate my location (changed slightly because of barrel proportions, of course) from that first gun. Did not use a TH liner. After drilling, I fired a few powder only rounds, and no flashes in the pan. Now I've had a day of shooting for working up loads--see my other post; that has not gone all that well, YET--and, still, if the priming charge ignites, the gun goes off.

I've seen several posts on here about TH placement, guidance, etc., and, of course, that's appreciated by all, myself included. And, as I said, I'm no "builder", by any means. Still several guns away from that. But I would like to know the science behind where I placed my TH. I'm just not that lucky very often.

I can say, studying on pictures of others' guns, it seems I place my hole just a tad higher.


Sorry for being so windy.

Hugh

 

[Slamfire]

Good idea, fire goes up. :v

 

[George Holton]

:thumbsup: You got it right the first time, Mine are placed just aa whisker above the top line of the pan, cant hit for manure but ther gun goes bang .

 

[nchawkeye]

I put mine where the frizzen covers when closed...

 

[paulvallandigham]

Slamfire has it right. The reason you locate the touch hole above the flash pan is because fire rises, or " goes up !" Have you ever really sat and looked at a candle burning? The hottest part of the flame is at the top, not the bottom. The reason fires rise, is because to become fire, you have to combine fuel, heat, and oxygen. Up is where more oxygen can be found.

Fire actually draws oxygen in from the sides and bottom, and causes drafts, whether the fire is big or small. In a flashpan, The construction of the device prevents much oxygen from coming in from the bottom( where the pan is), and the barrel prevents oxygen from coming in from That Side. So, if you want to fill the pan with powder, you have to leave a space above the powder for oxygen to move in under the flame, to get enough heat going to ignite the main charge in the barrel.

Put the touchhole, lined or not, about .030" higher than the top edge of the pan. If your happen to own a gun where the touch hole is lower, or like my rifle, was drilled so that the top edge of the pan divides the hole in half, half below, and half above, then you put less priming powder in the pan, and bank the powder away from the touch hole, to leave space under the hole for oxygen. This practice, however, reduces the size of your " target " for the sparks coming off your frizzen. If you are using a worn out flint, you might not get that one spark into your powder, and have a true misfire. As long as you understand this, banking the powder away from the barrel works, and works very well, I might add.

If you build your own guns, you can locate that touch hole properly, and then fill the entire pan with powder, increasing the size of the target, having a huge " burn " and insuring ignition of the main charge 100% of the time.

My gunmaker also widened the pan using a grinding wheel, and then polishes the surface to a mirror finish. The finish makes it very easy to clean with just one swipe of a cleaning patch. Removing residue makes it almost impossible for moisture to be drawn out of the air and spoil the priming charge in humid conditions. Widening the pan increases the size of the target for the sparks, so that you can set your flint, New, to throw sparks a little forward of the center of your pan, and then, during repeated firings, as the flint wears down, the sparks will continue to ignite the powder as they hit further and further to the rear of the pan. You get lots more shots out of a flint, before you have to use a twig to wedge the flint forward in the jaws to continue firing. I am getting 80-100 shots out of my flints, if they don't break, or chip out because of some defect. That means I am paying about 1 - 1 1/2 cents per shot at the cost of flints today. :hmm: I also like the idea that sometimes I can keep on shooting when the percussion shoots are going back to their cars to dig out another tin of caps for their guns. :grin:

There are good reasons for all of these things. Thanks for asking. :hatsoff:

 

[tg]

"and, still, if the priming charge ignites, the gun goes off"

This tells me that the hole location may be correct if I read your post correctly, unless there is a great deal of delay which could be attributed to a number of things, priming volume, picking/not picking vent, probably others I am not thinking of.

 

[Zonie]

IMO, the very rapid expansion of the priming powders flame front moves horizontally and vertically with equal speed and it is this flame front that passes thru the touch hole and ignites the main powder charge.

This happens so rapidly that I don't believe the less dense flame front has time to react with the higher density of the air around it like the flame of a candle does until long after the main charge has fired ("long" being 1/2 to 1 second after the priming has been consumed).

I feel that the reason for touch holes working better if they are located even or slightly above the top of the pan is because as the priming powder ignites and the flame front moves outward it creates a high pressure zone right ahead of it.

Because this high pressure zone cannot push the metal pan out of the way, its relative pressure is higher in this area than it is above the pans surface.

This higher pressure tends to deflect the unrestrained area of the flame front above it in a upward direction as it travels toward the barrels touch hole which results in a higher concentration of heat at the barrel just above the surface of the pan. This all happens in a few thousandths of a second.

This higher concentration of heat above the pan does a better job of igniting the main powder charge than it would do if the touch hole was positioned lower in the pan.

zonie

 

[paulvallandigham]

Ys and no. Have you considered why the outside of the flash pan is always rounded rather than cut( or cast) square? I think that semi-circle tends to direct the heat and flame towards the barrel as the fire is fist burning, as would any parabolic, or eliptical surface. I do think you are correct that the flame otherwise goes up and out to the sides equally. It is the heat that ignites the powder, and not the flame, apparently, although you and I both understand that what we see as a " flame " is only an visible spectrum characteristic of the heat generated by the burning of the flash powder. If you look at the same " flame " with infra-red or ultra-violet light filters, the " flame " looks much different, than what we see with our eyes, without such filters. I am confident that few scholars in the 17th, 18ht, and even the 19th centuries would have understood these subtleties, so I accept your reference to the flame as being accurate enough for our purposes. AND, everything we are talking about occurs within a few millionths of a second, so it is hardly visible short of using time-lapse photography to slow the process down for our poor brains. :thumbsup:

 

[John Taylor]

Slamfire has it right. The reason you locate the touch hole above the flash pan is because fire rises, or " goes up !" Have you ever really sat and looked at a candle burning? The hottest part of the flame is at the top, not the bottom. The reason fires rise, is because to become fire, you have to combine fuel, heat, and oxygen. Up is where more oxygen can be found.

Fire actually draws oxygen in from the sides and bottom, and causes drafts, whether the fire is big or small. In a flashpan, The construction of the device prevents much oxygen from coming in from the bottom( where the pan is), and the barrel prevents oxygen from coming in from That Side. So, if you want to fill the pan with powder, you have to leave a space above the powder for oxygen to move in under the flame, to get enough heat going to ignite the main charge in the barrel.

Sorry, can't go along with this.Powder don't need oxygen to burn, it makes it's own. The 75 percent salt peter ( potassium nitrate) is where the oxygen comes from. The 10 percent sulfur and and 15 percent charcoal are the fuel.
The reason the flame goes up is that hot air is lighter than cold air. Same thing makes hot air balloons work.

 

[paulvallandigham]

John: You are technically correct. But then, there is enough oxygen around a forge for coal to burn without shoving air at with a bellows, too, NO? We use more oxygen to increase the RATE OF BURNING, and thereby increase the pressure and temperature within the chamber. The faster both the temperature and pressure rise, the faster complete ignition occurs, and the ball is propelled out the barrel. Increasing barrel ignition time reduces barrel " lag " time, allowing the shooter to stay on target long enough to get consistent hits.

With percussion, and closed ignition systems, We all but eliminate one of two ignition delay problems that exist in flintlocks. In a flintlock we have a delay while the priming powder ignites, and burns enough to send heat and flame into the barrel chamber to ignite the powder there. Then we have the delay while the powder charge is consumed. With closed ignition, we actually burn a hole into the compacted powder, all but eliminating any delay in igniting the powder, and quickly igniting all the powder under pressure from the percussion cap or primer.

Its not enough to simply say Black Powder has its own oxygen. A fuse is a fuse. It may burn black pwoder, but it burns one granule at a time.

by opening a whole in the back of the chamber with a pick, we allow the fire to burn lots of granules all at once, so that instead of one fuse being lit, we have a dozen or more fuses being lit. By leaving more oxygen in the barrel, the fire gets hotter, and pressure rises faster, leading to faster production of gases under pressure to move the ball.If the early designers of cannons and the flintlock could have figured out a way to pump oxygen into the chamber at the point of firing, they would have. When I was helping to load my buddy's cannon, he pierced the load with a bronze pick down through the vent, and then either used cannon fuse, or priming powder to light off the charge. We found that we got faster ignition useing the 4Fg priming powder, even when the long vent created a slight " fuse effect". It took us some time, but we finally figured out that our cannon fuse had a wrapper around it, to protect the powder inside from moisture. But that also meant that ignition began at the top of the barrel even when the fuse continued to burn to the bottom, because only when the fuse burned enough of that outer layer so that heat and flame touched granules of powder would the charge ignite. We played around with fraying the end of the fuse that was pushed down into the chamber, but found nothing that would speed ignition, that way. We did also play around with the powder chosen, and were surprised when 1Fg actually ignited faster in the cannon than FFg powder did. The only explanation we could find was that the size difference between the two powders left more air in the powder charge, and that was what was speeding ignition, even though the actually pressure created was lower.

 

Well, you got some dissertations...the accepted touchhole position is centered and even with the top of the pan. However I find your hole position interesting. I have a rifle from a relatively well known maker and it is also a tad high. When I first got the rifle I had trouble with misfires and questioned the location. The man stuck by his guns, so to speak. Finally I opened up the hole a bit, that helped but still a few misfires. Later I figured out most of my problem was a bad batch of Elephant powder, as the problem went away when I changed to GOEX. Since then I have seen several other examples of a high touchhole--and one example of a double touchhole [one above the other straddling the pan line]. I have also seen guns with the touchhole "too low" that still worked fine---I guess there is some 'slop' to the situation...

 

[Longsmoke]

The relationship between primer and main charge are not effected by the fact that heat rises no more than the affect of a nuclear bomb is. It takes to long for this effect to take place, by the time the heat from the primer starts to rise the ball is already moving because the heat is still under the influence of the explosion (a much greater force). What lights the main charge is the expansion of an explosion much like the heat affect from a nuclear bomb 2000 ft. below the burst. The expansion of black powder takes the heat and still burning grains with it (until the force of the explosion is lesser than that of heat rising). It also expands in all directions as it burns. The flash pan not only holds the powder but also effectively turns the primer into a shaped charge giving the explosion direction.

Placing the touch hole a tad above the pan gets it a little closer to the center of the directed blast, it only increases the odds of ignition. It also helps keep the primer in the pan and not in the flash hole. Primer in the flash hole acts like a fuse that has to burn to the main charge slowing ignition. That’s why Jim Chambers’ touch hole liner works so well as it brings the main charge closer to the primer charge.

Paulvallandigham no offence but are you are contradicting yourself. The smaller the powder grain the faster it burns because of the time it takes to burn the volume of each grain. If you have equal amounts of 1F and 4F the 4F will make more pressure in the chamber than the 1F because the smaller grains will burn faster and consume the whole charge in less time. If you were right about the available oxygen in the chamber of the cannon when loaded with 1F then the bigger powder grains would make more pressure. How did you measure the pressure? I’m not saying the oxygen in the bore does not burn but, it does not influence the burn rate of black powder.

Your friend uses the poker in the touch hole of the cannon to puncture the powder bag. If he is not using a powder bag there is no need to for this procedure. The reason ignition is faster with primer than fuse is, fuse has a predetermined burn rate (much slower than lose powder). Neither uses an outside oxygen source and neither will be influenced by available oxygen

Bruce Everhart

 

[paulvallandigham]

Bruce, our cannon fodder was made in an aluminum foil container, made by first wrapping foil around a soda pop can, then loading the powder and flour( a filler used to create pressure and some smoke) before closing the front end. The prick went right through the foil container to open a hole in the charge.

It may sound contradictory to talk about FFg burning faster when packed loose, but that is how it works! Try it for yourself. Packed FFFg powder does not ignite as fast as loose FFg . We are talking milliseconds, but I noticed the difference in the difference in movement of my front sight when shooting off a rest. I have compacted FFg , and FFFg powder in the same gun, same load, and then compared them to loose loads of both. Finally we ran those experiements over a chrnonograph. The packed FFg powder produces slightly higher velocity than the loose FFg charge of the same size, but that is corrected easily by adding a few more grains of powder. What we did find was that the loose powder load gave a smaller SDV than did the compacted powder charge, and better groups, off a rest.

Loosely loaded FFFg also ignites and burns faster than packed FFFg powder, IN A FLINTLOCk. The contrary occurs when using Percussion ignition and FFFg powder. You get a smaller SDV using compacted FFFg powder in a Percussion rifle, than if the powder is loaded loosely. And, better accuracy off a rest.

Make your choice of using FFFg or FFg powder based on how a given load burns in a given gun for you, and the kind of cleaning procedure, lube used, etc. in loading your gun.

I clean between each shot, so that all shots go to the same POA as my first shot out of a clean barrel. Other shooters like to go all day without cleaning. I have found a few LOADING PROCEDURES that give promise for allowing me to do the same during most months of the year here in Central Illinois. It may differ where you live.

If you are then looking for the most accurate load for your rifle, THEN having chosen the powder you want to work with, test some shots over a chronograph( simply because it is the easiest way to eliminate human error) to see what the SDV is for both a compacted powder charge, and a loosely loaded charge. Use whatever is the best in your gun. Then, if you are curious, try the same test using the other powder. Check the velocities, and group sizes, and then check the SDV. Choose the best of the four tests for your Best Load, and let us know what you find. Thanks.

 

[tg]

I have often wondered how the depth/shape of the pan may affect ignition the vent may be in a position relitive to the top of the pan but some pans are a lot deeper than others this could concievably have an affect on things but probably a small one, as in some pans the top of the prime will be a different distance from the vent due to pan depth, just a thouight, I have always had good lucck with the vent pretty much in line with the top of the pan, even with a plain old fashioned 5/64 hole.

 

[Owen]

If I may Ask, I’m about to drill a touchhole on my first barrel and build . So how far from the wall of the breach should the hole be. I would think if it is to close to the wall fouling could be a problem but if it is to far away it might not set off smaller powder loads. The barrel is a 20Guage smooth bore.

Thanks.
Owen

 

[tg]

Often the face of the breech plug is relieved to allow for a vent that is set back a ways, possibly due to a pre-inlet lock mortice, the last one I set up had the back of the hole flush with the breech plug this was using a plain hole and no liner, some of the more experienced builders here may chime in with some more advice on how they calculate their poistion of hole/liner, I am admitedly a novice gunstocker not a journeyman builder

 

[Longsmoke]

Owen
Somewhere between the breech face and half the diameter of the bore from the breech face. In other words a 20 g. being about 5/8” would make half the bore about 5/16”. You do not want go farther forward than that, closer to the breech is better. Any more than that would make it possible to cover the touchhole with a fully seated ball (with no powder). I don’t think you ever use a charge smaller than the available space left by a ball touching the breech. And, if you ever seat a dry ball you will be able to get enough priming powder through the touch hole to push the ball out.

Keeping this in mind, it is more important to locate the hole to the lock (see previous comments). This why most builders do not like pre inlet lock panels.

Read tg’s last post again. I like to locate the lock as far back on the barrel as I can, keeping function in mind. If the hole is flush against the breech you should have no problem with fouling. If you do it is because the is to small. What size hole do you drill tg? I use Chambers’ touch hole liners and open them to .062”.

If I missed something please ask.

Now, in support if my previous comments about heat v explosion please fallow the link below.
[url] http://www.youtube.com/watch?v=GzgVnH6uEP0[/url]

Bruce Everhart