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Are we sure tapered touch hole liners are a good idea?
- Thread starter Dartwick
- Start date
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Phil Coffins
69 Cal.
The diameter of the hole is the restriction to the pressure, the length of the hole is reduced by coning the inside or out of the vent.
hanshi
Cannon
The liner should have a coned rear face to go in the barrel. This way only a thin layer of steel - with a 1/16th" hole - stands between the bore charge and the prime.
That is the way I always figured it.
On some originals the TH was coned from the inside, without use of a liner. Before the breechplug was affixed, a special 2-piece cutting bit was inserted through the TH (shaft from the outside, cutter from the inside) to cone the cast iron barrels. I have a modern replica of one.
Not necessarily akin to being a venturi ...
Not necessarily akin to being a venturi ...
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I wonder how many pages this thread will go.
Personally I think there are more reasons to have a liner than not to, yes there may be a very slight velocity loss however, depending on how thick the barrel wall is you essentially have a fuse which will increase the ignition time from pan flash to igniting the main charge. This will increase the possibility of moving off point of aim, especially shooting off hand.
It's hard enough to stay on target with a fast ignition let alone a rifle that has a slight hang fire.
Personally I think there are more reasons to have a liner than not to, yes there may be a very slight velocity loss however, depending on how thick the barrel wall is you essentially have a fuse which will increase the ignition time from pan flash to igniting the main charge. This will increase the possibility of moving off point of aim, especially shooting off hand.
It's hard enough to stay on target with a fast ignition let alone a rifle that has a slight hang fire.
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Since I discovered this ... coning the inside AND just a slight cone on the outside as well ... makes it a very fast ignition.
For me, I would way rather have a fast ignition and sacrifice, what maybe 20 FPS in velocity. Can't see that having the cones in place will lessen much more velocity than that. When I find that the side expulsion gets a bit outta hand. Then I would measure the touch hole and then if too large, replace the hole liner.
My 2 cents.
For me, I would way rather have a fast ignition and sacrifice, what maybe 20 FPS in velocity. Can't see that having the cones in place will lessen much more velocity than that. When I find that the side expulsion gets a bit outta hand. Then I would measure the touch hole and then if too large, replace the hole liner.
My 2 cents.
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I'm still in the investigation faze of this theory and as I make my own vents of A-2 stainless tool steel I will have the opportunity to see first hand how well some of these ideas work.
I have enough experience with White lighting liners ( shooting next to them and seeing how they vector internal breech pressure far out the side) to not care for them.
I much prefer to cone the outside to vector pan flash inward and discourage breech pressure flow outward.
I also believe that a funnel effect is more representative of pressure flow physics in a flint lock than is the Venturi action often used to describe it, which is what occurs from percussion nipple interior profile.
A funnel in a hose or drain will facilitate much more volume of flow than will a flat surface into the pipe which is what we want on the inside of a vent to hold back more of the breech pressure. On the pan side of the vent we want a funnel shape to encourage pan flash flow inward to the main charge as well as decreasing the length of it's passage it has to move.
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After you get done with your investigation please let us know what you found.
Back in the early 1970's , guys were using factory guns and installing the correct size Allen set screws in place of the factory removable vent liners. The Allen set screws had exactly the same threads as the factory liners ,and were easier for neophyte gun owners to remove and clear a dry ball , and or clean a fouled barrel . The Allen wrench hole was on the outside of the barrel and in all honesty ,I never found a need to have the system on any flint rifle I had. Both standard touch hole liners , and the Allen screw with atouch hole drilled through it shot with the same Ignition speed. The draw back to the Allen screw touch hole was , Allen screws were much harder than the gun barrels in use , and eventually ruined the threads in soft steel barrels from repeated removal and heavy handed tightening on re- insertion of the hardened Allen screw touch hole. ........oldwood
I can see where a larger diameter vent hole could cause velocity loss and/or accuracy issues due to inconsistent pressure. Same way an eroded nipple can mess up a caplock. I don't know that coning in or out or both would result in the same pressure loss. The vent is the vent, that's the only place for pressure to leak out.
Touch hole knowledge?? Late 1970's into the mid 1980's , I shot rifle competition with a Getz barrel , 44" .50 cal long rifle. It was a tack driver , until the touch hole liner got so eroded , the load consistency deteriorated and accuracy fell off. There were two things effecting the poor accuracy I saw. One was the touch hole erosion , and the other was bore erosion. Was easy to change out the touch hole liner ,but had to go to a .005 thick patch , and ball size from .490 to .495. Accuracy came back for as long as I kept the rifle.............oldwood
rdane
40 Cal
way back in the early 70s, in the Dixie gun works catalog, they did a test, and showed that a flint gun produced greater velocity than a percussion gun. They said that as the projectile moved forward it sucked more oxygen in through the vent and caused a better burn of the powder.
We're getting in to the arcane stuff here. Need a physics class to prove or disprove that. Not that it doesn't make reasonable sense, but could it be enough velocity to matter? There has to be a point of diminishing returns, like eroding vent holes eventually becoming a negative.
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You have rapidly expanding gasses at a higher pressure than the outside air. Physical properties don't allow gas to fly from a low pressure to a high oressure.
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The NMLRA magazine, Muzzle Blasts, did testing on this in the last issue and disproved the "fuse effect" idea, and the idea that sloshing the powder in the pan away from the touch hole results in faster ignition.
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Yeah, well I will keep using White lightning vent liners. They work for me and have worked very well.
I went back and read the article, it was about the position of the priming in the pan. I would like to see someone do an experiment with a 32 caliber in a 1" barrel so there would be a nice long section of barrel between the pan and the main charge, then drill it out and put in a liner, that would be the test.
I went back and read the article, it was about the position of the priming in the pan. I would like to see someone do an experiment with a 32 caliber in a 1" barrel so there would be a nice long section of barrel between the pan and the main charge, then drill it out and put in a liner, that would be the test.
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My Kibler SMR came with a White Lightning vent liner already installed. They are reputed to be fast, and outlast other liners.
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The idea of an inside cone is to bring the main charge closer to the priming charge. The result is faster ignition.
No internal cone would be like a straight drilled touch hole, so why bother?
Of course, touch hole size affects pressure, and an oversized touch hole, can change accuracy, just like a burned out nipple.
Due diligence, change to a new touch hole every 10,000 rounds.
Not rocket science.
No internal cone would be like a straight drilled touch hole, so why bother?
Of course, touch hole size affects pressure, and an oversized touch hole, can change accuracy, just like a burned out nipple.
Due diligence, change to a new touch hole every 10,000 rounds.
Not rocket science.
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