Touch hole liners??????????

[Cody Tetachuk]

It's pretty clear, I think, that muskets had straight touch holes, and armies considered reliability important.  

Perhaps the "reliability" that the military was concerned with was TH longevity. Everything I've seen/read suggests that TH erosion was a common problem, likely due to the soft iron that the barrels were made from. If a simple TH drilled through the side of the barrel had, what we would consider premature erosion problems, what would the life expectancy be on one that was internally coned? The military would be more concerned, IMO with ruggedness and longevity more so than ignition speed and efficiency.

Anybody actually growing up shooting only flintlocks and never shooting percussion or cartridge guns, probably did not have the sense that ignition was slow.  I propose this is a modern thought; natural for those of us who have experienced faster ignition.  We want to 'fix it".  They did not know they had a problem, IMHO.

That's a good point regarding the 'average' shooter. However, I know serious target shooters TODAY that install titanium firing pins and springs to reduce lock times on their target rifles. I suspect that serious shooters of the day knew full well that their lock times were not as good as they could be and were looking for ways to improve them. Just like today, the average shooter/hunter finds the lock times that they are accustomed to to be quite acceptable. Then again, all this depends on whether we are discussing wether or not TH liners were USED on period American rifles or wether or not they offer improved ignition. Two completely different discussions.

[Daryl]

Don' tknow about America - but look to the Nock breech cuttaway to see an internally coned vent liner.

[Larry Pletcher]

. . . . .Thus a smooth transition into the orifice as well as a short channel will keep the flow velocity up rather than diminish it.  Better than simply chamfering the outside would be to have a radial inlet transition from chamfer to vent orifice.   How much better is difficult to quantify by speculation.  But in essence any gradual transition to the final orifice diameter is better than an abrupt perpendicular, sharp transition.  

Just some food for thought and discussion. ...

Rootsy,
Thank you for your thoughts.  Another ALR member sent a private message about the same thing.  He called it a "parabolic curved entry", and attached the following photo:



I hope the writer will step in here.  As an example he used the intake horn on a '60s hot rod.  I am not well versed on fluid velocities through a hole, but I'm sure willing to learn.
Regards,
Pletch

[Acer Saccharum]

Does it whistle when the gun fires?

[rich pierce]

It's pretty clear, I think, that muskets had straight touch holes, and armies considered reliability important.  

Perhaps the "reliability" that the military was concerned with was TH longevity. Everything I've seen/read suggests that TH erosion was a common problem, likely due to the soft iron that the barrels were made from. If a simple TH drilled through the side of the barrel had, what we would consider premature erosion problems, what would the life expectancy be on one that was internally coned? The military would be more concerned, IMO with ruggedness and longevity more so than ignition speed and efficiency.

Anybody actually growing up shooting only flintlocks and never shooting percussion or cartridge guns, probably did not have the sense that ignition was slow.  I propose this is a modern thought; natural for those of us who have experienced faster ignition.  We want to 'fix it".  They did not know they had a problem, IMHO.

That's a good point regarding the 'average' shooter. However, I know serious target shooters TODAY that install titanium firing pins and springs to reduce lock times on their target rifles. I suspect that serious shooters of the day knew full well that their lock times were not as good as they could be and were looking for ways to improve them. Just like today, the average shooter/hunter finds the lock times that they are accustomed to to be quite acceptable. Then again, all this depends on whether we are discussing wether or not TH liners were USED on period American rifles or wether or not they offer improved ignition. Two completely different discussions.

For sure, 2 different discussions.  Tests indicate internally coned liners provide more reliable, and maybe 10%  faster ignition.  But I do not know of evidence that they or internally coned touchholes were used in appreciable numbers on American-made military or non-military arms of the 18th century.

[Rootsy]

In fluid dynamics where you are looking at flow through an orifice you have what are called K factors where each transition change in the flow path is factored on how much it impedes or assists flow.  

A quick google search brings this as the first result... Read the first few sentences and then bypass all of the diff-e-screw and calculus and scroll down to the diagrams...  

http://www.mcnallyinstitute.com/13-html/13-12.htm

[T*O*F]

I am not well versed on fluid velocities through a hole, but I'm sure willing to learn.

Pletch,
I would think you would already know all this stuff.  There is nothing new in this thread that we didn't cover on the old MLML  12 -14 years ago, when we had rocket and fireworks guys as well as numerous engineers.

Maybe the subject wasn't of sufficient interest for your level of testing back then and you forgot about it already.

[davec2]

You guys are WAY over thinking this whole touch hole thing.  I am a rocket propulsion engineer (for the last 25 years) and deal with hot gas flows through  orifices and nozzles all the time.  However, the web site noted deals with incompressible flow (i.e liquids through an orifice).  With a touch hole, we are dealing with compressible flow (i.e. gas, not a liquid) through an orifice.  This is an altogether different situation.  And, on top of that, before the gun fires, and with only the first flash of the powder in the pan, there is very little pressure differential across the orifice (touch hole) driving the flow in either direction.  So, in my opinion, it is not a fluid dynamics issue or a thermodynamics issue but a pyrotechnic issue.  The bigger the touch hole, including a taper one way or the other, the shorter the narrowest part of the burn path, the quicker the propagation of the flame front will progress into the main charge, the chamber pressure will increase and the burn rate will reach its maximum.  The longer, skinnier the hole to burn through, the longer the pyrotechnic train burn time required to get the main charge lit.  I really don't think it is any more complicated than that.

[Larry Pletcher]

Pletch,
I would think you would already know all this stuff.  There is nothing new in this thread that we didn't cover on the old MLML  12 -14 years ago, when we had rocket and fireworks guys as well as numerous engineers.

Maybe the subject wasn't of sufficient interest for your level of testing back then and you forgot about it already.

Fox,
I went back and looked at the MLML archives that I saved.  I couldn't find any reference to the exterior of the hole shape except when I brought it up.  All I found was straight cylinders and discussions of the interior of the liners.  I expect that any fluid dynamics discussions was before I joined.   I was too interested in vent speeds to have ignored such comments.
Regards,
Pletch

[Larry Pletcher]

Dave,
I just saw your post as I was hitting "send".  I'm very interested in your thoughts.   I hope I understand what you are saying.  Do you think the exterior shape of the vent has any effect on flame through the vent?  In my mind I was already thinking how I could test that idea.   I hope you don't mind my picking your brain.  The only thing more fun than teaching is learning -- or maybe it's the other way around.

Regards,
Pletch

[rich pierce]

Dudes, are you looking at this bass-ackwards?  If I am thinking correctly, the important thing is how quickly the flash in the pan lights the main charge- not how well the whole thing blows gasses out of the vent. 

[Daryl]

I see any coning on the outside, as counter-productive as it moves the powder away from the flash in the pan.  this is in comparrison to a whitelightening liner, in which the powder is separated from the pan by a thin web of steel.  If that web was thick enough to allow any dishing on theoutside, it may increase ignition speed in THAT gun, but the powder is still much farther away from the pan than a vent that allows powder right beside the pan.  When you glance at a WL liner on a laoded gun, you can see the main charge powder - just ichin to ignite.

[Pete G.]

I agree with Daryl. It is just your basic time/speed/distance calculation. The speed of the flash stays pretty much constant, therefore any change in distance causes a directly proportional change in speed. 

BTW: Does anyone know how many angels can dance on the head of a pin ?

[Rich]

I've given this some thought. As I see it, the issue is not the flow out of the vent, but from the pan into the powder charge. Without a vent, the heat, flame or whatever sets the charge off, has to travel through a tube, the straight drilled vent. The question is, does the flame/heat arriving at the powder charge lose any power to set off the charge by traveling through the straight vent rather than the counterbored vent? Does it take longer for the main charge to ignight because of this? If the counterbored vent moves the charge closer to the pan. Does the distance from the pan to the powder make any measurable differance? I don't have any answers but my guess is a vent is faster.

[Larry Pletcher]

No, richpierce, I'm still thinking about gases entering the vent.  Nor am I thinking of a vent that uses a longer web than a white lightning.  If anything, the web would be thinner, maybe too thin.  I'm wondering if we can reshape the space from the inside of the web to the barrel surface.  I already use an exterior cone on a White Lightning.  Instead of a cone with a straight angle (as in a counter sink), can I radius the cone?

Keep in mind I have a lot more questions than answers.  If I could draw worth a hoot, I'd sketch this.  Never mind, I'll try anyway.  When drawing is my only way to communicate, I'm in trouble.
Regards,
Pletch

[Acer Saccharum]

Larry, a touch hole with radiused edges will hold up better than one with sharp corners. I don't know about speed of gasses passing thru the different shaped holes. I am guessing that you'd get higher velocity through a hole that has rounded or softened edges rather than a sharp edged hole, even if the two have the same diameter and same length.

But this is something for the Ignition Sleuth to discover.

With a radiused hole, will you get a venturi effect? Can you use a smaller hole and still get same ignition speed?

[KNeilson]

I had an eloquent post all typed up and I lost it in one swoop of the keyboard. The vent pic Larry posted is mine, on my first rifle. I make no claim as to whether it is an improvement or not. The thought was to create a "venturi"effect, I dont know if it really does tho......Davec2 brings up a good point

we are dealing with compressible flow (i.e. gas, not a liquid) through an orifice.  This is an altogether different situation.  And, on top of that, before the gun fires, and with only the first flash of the powder in the pan, there is very little pressure differential across the orifice (touch hole) driving the flow in either direction.

As this theory is driven by a press difference there may not be a whole giant effect, seeing the flash is in the open, the press difference will be quite small.....
Daryl has another...

I see any coning on the outside, as counter-productive as it moves the powder away from the flash in the pan.  this is in comparrison to a whitelightening liner, in which the powder is separated from the pan by a thin web of steel.  If that web was thick enough to allow any dishing on theoutside, it may increase ignition speed in THAT gun,

There is a .050 web, which I cut back a bit with radiusing the entry, itself is about .020 deep.. 
My radius does come outside the pan, this is a concern to me that I`d rather not have to fix.
After watching the High speed videos I am thinking all of this is interesting discussion, but how much use it has on a practical sense I dont know. Whether you start the main charge burning with one powder kernel or a bunch, is there a noticable difference in the time it takes to consume all of it. I wouldnt think so. If someone is willing to test all of this I will be watching with gret interest..
From Davec2 post...

So, in my opinion, it is not a fluid dynamics issue or a thermodynamics issue but a pyrotechnic issue. 

  this is probably more true than all else, simply put, the closer, the better......
In my very humble opinion........  Kerry

[Larry Pletcher]

Larry, a touch hole with radiused edges will hold up better than one with sharp corners. I don't know about speed of gasses passing thru the different shaped holes. I am guessing that you'd get higher velocity through a hole that has rounded or softened edges rather than a sharp edged hole, even if the two have the same diameter and same length.

But this is something for the Ignition Sleuth to discover.

With a radiused hole, will you get a venturi effect? Can you use a smaller hole and still get same ignition speed?

Acer,
All those questions are what I'm wondering about.  Here is my weak try at a drawing:


As I try to think this through, I could see that the WL web would be decreased or the liner would need to be set in deeper to make room for the radius work.  In this mental problem,  I don't want to the web to be increased. 
Kerry, I just read your post before I hit "Send".  Thanks for your input.  My drawing isn't an elegant as yours.  While this may turn out to be a mental exercise, I'll take any chance to learn.

Regards,
Pletch

[KNeilson]

you'd get higher velocity through a hole that has rounded or softened edges rather than a sharp edged hole

My hole point, pun intended........   Kerry

Larry, a touch hole with radiused edges will hold up better than one with sharp corners

this is good to know, I didnt before...... K
Larry,

  While this may turn out to be a mental exercise, I'll take any chance to learn.

...this is why I`m here.K

[Daryl]

I would think a vent with sharp edges would hold up, ie: last longer than aa vent with rounded edges.  The vent with square or sharp edges would take some # of shots before those edges became worn to rounded shape - THEN, the rounded edges would probably last as long as those that were pre-rounded.
You can adjust the thickness of the web of a WL liner, by how deep the chamfer is on the outside of the hole you've bored and threaded.  Seating the liner as deeply as possible, then chamfering the outside to reduce the thickness still moves the powder away from the pan's flash.  It probably doesn't matter for all of you who can hold longer or steadier than I, but I need every 'assist' I can get therefore a milisecond or two faster average ignition could help my meagre shooting abilities with a flintlock.

[smylee grouch]

When I was instaling the WL on my current hunting rifle I ended up with just a hair more web than I wanted after I had filled the liner flush, so I took an engraving tool and relieved a small amount on the bottom of the hole, thinking it might help the flash get up into the liner when it jumps off the pan. I dont really know if this works that way but I have a very fast ignition on this gun. Someone might tell me it doesnt work like that  but like I said, its fast. Have you tried anything like that Larry?       Gary

[omark]

we have been discussing gas flow through the vent. is it possible that ignition is caused by radiant heat rather than gas flow?? just kinda thinkin out loud.     mark

[Dphariss]

I see any coning on the outside, as counter-productive as it moves the powder away from the flash in the pan.  this is in comparrison to a whitelightening liner, in which the powder is separated from the pan by a thin web of steel.  If that web was thick enough to allow any dishing on theoutside, it may increase ignition speed in THAT gun, but the powder is still much farther away from the pan than a vent that allows powder right beside the pan.  When you glance at a WL liner on a laoded gun, you can see the main charge powder - just ichin to ignite.

The problem with external cones, in my experience, is that they are more prone to flashes in the pan if they have any fouling the the external cone or even not. I have had unexplainable flashes with external cone vents. I have never had an unexplainable flash  with the WL/English type.

The late English locks have vent wipers and the vents were remarkably like the White Lightning since they are apparently what the WL is based on.
I do know that with the vent wiper and the WL style liner a flintlock is VERY reliable. The only thing that will produce a flash is if a flake of fouling gets into the liner and blocks the vent, the rifle will flash and then its necessary to break the flake of fouling with a pick or grass stem (I seldom carry a pick). This is the only thing that has caused the rare flash in several hundred rounds with this rifle.
The only other factor is wind. In reading old accounts I heard of people claiming that the wind blows the fire out of the pan of a FL, it can happen if the wind is strong enough. It is more likely with a "simple vent" than a good liner but neither is proof against it.
I KNOW that SS liners are not HC. But I don't care. The rifle has to WORK. Along with some others here I hunt areas where there are large carnivores with bad attitudes at times. You just don't knwo what time.
Then there are places where the bears come to gunshots.
So the person that shoots in matches or re-eneacts has a different view so reliability than I do. I also don't like conducting a long stalk perhaps a mile from spotting to the shot and then having a flash in the pan.
I started shoot FLs 40+ years ago and have used "plain vents" but not in the last 30 years or so.
As Daryl mentions here, when I load a WL I can see main charge powder within .020" or less of the pan. The Nock breech rifle often has a granule protruding from the vent after loading since the vent is over .065" on this rifle.
Dan

[Dphariss]

we have been discussing gas flow through the vent. is it possible that ignition is caused by radiant heat rather than gas flow?? just kinda thinkin out loud.     mark

It has to be radiant heat there is not over pressure at the pan to force gases into the vent any distance since this would require compressing any air in the vent since the bore is sealed.

Dan

[Larry Pletcher]

You can adjust the thickness of the web of a WL liner, by how deep the chamfer is on the outside of the hole you've bored and threaded.  Seating the liner as deeply as possible, then chamfering the outside to reduce the thickness still moves the powder away from the pan's flash.

Daryl,
I agree that you can set the WL deeper.  How about this: we seat the liner .010" deeper and then take that .010" off the outside in the form of a flared exterior cone.  The flare is so shallow that there really isn't a cavity outside.

I don't think this moves the powder away, especially because of the way I prime the pan.  I want my prime against the barrel no matter what the external barrel shape is - flared, coned or flat.   In the tests I did last summer, the closer the prime was to the vent the better the flame travel --- even if the prime covered the vent!

An additional thought is that when the web is only .020" apart, maybe we should think of the barrel charge and the prime as a single charge - and not 2 separate ones.

Too late for me.  Fingers won't type what I'm thinking. 
Regards,
Pletch