Touch hole wall thickness

[Dan Fruth]

Hi folks...I am wondering if any tests have been done to see the speed of ignition vs touch hole wall thickness. Using a coned liner with a .067 vent and differing amounts of wall thiskness. Your thoughts would be appreciated.....Thanks...Dan Fruth

[Acer Saccharum]

Yes, the wall thickness makes a big difference in ignition time. On a recent build, with an .068 touchhole, I had an estimated wall of about .05 long. I had noticeable slow ignition. I reduced the wall to about .025 and much improved speed.

[Larry Pletcher]

Hi folks...I am wondering if any tests have been done to see the speed of ignition vs touch hole wall thickness. Using a coned liner with a .067 vent and differing amounts of wall thiskness. Your thoughts would be appreciated.....Thanks...Dan Fruth

Steve Chapman and I plan to do this with a vent made with Tom Snyder's vent tool. We will probably will do .020" vs .040" although nothing is cast in stone.  I would like Ian Pratt's help - according to Tom, Ian has a cool way to measure this.

For testing already completed on vents look at "Pan Vent Experiments" . It's found in the feature articles list at www.blackpowdermag.com

Regards,
Pletch

[Acer Saccharum]

As always, Pletch, your work is much appreciated. I offer you all my machining services.

[Dan Fruth]

I'm currently waiting for another of Tom's little coning tools, as I broke a chip off one within >09 off the outer barrel wall. I measured the wall by placing a piece of silly putty on the end of some long nose plyers and squishing it into the cone, making sure it pushed it's way to the outside of the barrel. I just pulled it back out and measured the length. it was 3/32 long. I used silly putty often in the tool room to measure hard to reach areas, and it works quite well.

[Larry Pletcher]

As always, Pletch, your work is much appreciated. I offer you all my machining services.

Hi Acer,
As usual, My complements for your kind offer.  Steve's daughter got married this week, and he is pretty well tied up for a while.  It will be a while until we start.  We intend to time the vent webs on a half stock hunting gun.  The only machining needed will be to cut the actual vent.

The actual time will be from photo cell at the pan until fire at the muzzle.  Because of that we can't compare these results with previous testing.  It will work for the differences in web thicknesses on this barrel.  If the process doesn't work, we have a couple of barrel stubs that could work.  Our thought though, was to do this at normal shooting velocities.

Regards,
Pletch

[kutter]

Is there a safety factor involved in that somewhere? Can wall thickness become so little in the attempt to decrease ignition time that safety (blowout) is compromised?

[billd]

I don't think blowout would be as much of an issue as accelerated erosion.


Bill

[Daryl]

Is there a safety factor involved in that somewhere? Can wall thickness become so little in the attempt to decrease ignition time that safety (blowout) is compromised?

The thinner the wall, the quicker the ignition of the main charge and the more quickly the vent hold 'wears' larger. It's all a toss-up. as to blowout, enlargement is the problem which creates much more and further blast of hot sparks- which endanger bystanders not watching where they are standing or walking.

[Larry Pletcher]

Daryl,
I suspect we both like barrel charge and priming close enough to shake hands.  I probably said this before, but igniting two charges .020" apart is like igniting a single charge IMHO.

I'm looking forward to this test because I don't thing it's ever been done. Though, the difference in speed between a .020 and .040 vent web may be pretty small to measure. We'll see.

Regards,
Pletch

[kutter]

Is there a safety factor involved in that somewhere? Can wall thickness become so little in the attempt to decrease ignition time that safety (blowout) is compromised?

The thinner the wall, the quicker the ignition of the main charge and the more quickly the vent hold 'wears' larger. It's all a toss-up. as to blowout, enlargement is the problem which creates much more and further blast of hot sparks- which endanger bystanders not watching where they are standing or walking.

Thanks, hadn't thought of the hole eroding. I know not to stand to the right of the shooter!

Just wondering with it so thin if there would be a safety issue.
With all the concerns with the fit up of the breech plug for safety and then just in front of & to the right of it make a spot in the bbl wall .020" thick made me ask the question.
Perhaps the exteme small diameter is in play also.
Thanks!

[Dan Fruth]

I spoke with Jack Haugh this weekend and he makes his own vents with a 1/64th thick wall. He drills a .07 hole in the liner, and c-bores the inside untill he is as close to 1/64" as he can, and installs. He uses 1/4-28threads and SS for the liner......My concern with Tom's little tool is this......The rifle I built used a rather "high" lock placement, and the vent was just a bit over 1/8th from the 45 degree flat. If or when that burns out, I'm not sure how to address the problem with a liner. I won't have enough room to install a 5/16-32 hole without getting into the angle flat......SO I'm not willing to go for too small wall thickness as that will mean quicker burn-out of the hole.

[Larry Pletcher]

I spoke with Jack Haugh this weekend and he makes his own vents with a 1/64th thick wall. He drills a .07 hole in the liner, and c-bores the inside untill he is as close to 1/64" as he can, and installs. He uses 1/4-28threads and SS for the liner......My concern with Tom's little tool is this......The rifle I built used a rather "high" lock placement, and the vent was just a bit over 1/8th from the 45 degree flat. If or when that burns out, I'm not sure how to address the problem with a liner. I won't have enough room to install a 5/16-32 hole without getting into the angle flat......SO I'm not willing to go for too small wall thickness as that will mean quicker burn-out of the hole.

My gut says it will take a LOT of shooting to erode the vent badly enough to require attention.  It it does need work, Jim C sells a smaller size 1/4x32 that would help your vent positioning.  He will also supply the liner in non-stainless - making it harder to see.  There are other options as well.

Regards,
Pletch

[Dan Fruth]

Thanks for the "gut" response.....12L14 is easy to work, and my guess easy to burn out. I'm not worried about rust, just burn out....But I'm not living with the rifle in my hand every day, so I think you are correct..Will take a lot of shots to spoil the vent. When finished I'm shooting for .03 wall thickness....That should be enough safty/speed factor..Dan

[Jim Kibler]

My beleif is that the thickness of the wall has more to do with consistent ignition and the touch hole staying clean rather that changes in speed for consistently clean holes.  If I remember correctly, the difference Larry found between a coned hole and a simple drilled vent was only somewhere around 20% if the holes were kept clean.  Hopefully Larry will correct me if I'm wrong with this figure.  Personally I have found the hole stays cleaner and ignition is more consistent with a narrow wall thickness.

[Daryl]

I-too am looking forward to Larry's test. They are always of value and the data most eagerly absorbed by many here.

I've always looked to a thin wall as being benificial and like to be able to see the powder through the hole, next to the pan.

I do have experience with a too-thin wall burning out quite quickly, perhaps only a couple thousand shots and it was totally self-priming with 3F. It's the reason I experimented with 2F in my .45, then the .40 finding duplicate accuracy and speeds if using 10gr. more of it than 3F  with LHV lube.

[Acer Saccharum]

Yes, erosion is a problem for long term accuracy, but it's not really a concern for me. I am not a real target shooter, who depends on consistent pressure, shot-toshot- all day long, all year 'round. I don't know what it would take to wear a vent out.

A steel vent pick probably contributes some wear and tear.

If the vent is well designed and constructed, the vent will pretty much 'self-clean'. I seldom have any issues with the vent, other than 'operator error' of shoving all the bore crud to the bottom of the bore... blocking the vent with wet goop.

As mentioned above, I shortened the vent wall from .05 to .025 and noticed an increase in consistency and speed.

On the other hand, I had shot my rifle with an unconed, unlined touchhole, and ignition went from bad to worse. The barrel wall was about 3/16. So what Jim K applies: a clean touchhole is pretty good.  But a dirty one is poor, and next to impossible to get consistent ignition. Makes you want to switch back to a matchlock.

[bgf]

Erosion is probably not an issue on a "hunting rifle" that gets a few shots a year, but if you shoot regularly (e.g., matches and practice) a vent or liner will burn out pretty quickly.  I burned out a liner in a year/<1500 shots.  It was the cheaper kind of stainless one, but I would think barrel steel would erode much more quickly, and the few numbers I've seen say that even the gold standard -- a stainless White Lightning -- is burned out possibly in 3K shots (which would be only a couple of years or less for some).  The non-stainless variety of WL liner is supposed to burn out in a few hundred shots or so, from what I've read.  Anyway, for hunting rifles and wallhangers, a drilled coned vent with thin web may be just fine, but I would watch for signs of erosion and consider the application.

Just as a disclaimer -- these numbers (except for my own experience) are what I came across when researching.  If anyone has better/more data, feel free to correct or expand on them.

[billd]

At Dixon's last year I asked Jim Chambers about his steel vent liners thinking they would look better.   He told me they may only last 300 shots.   He said his stainless ones would last several thousand.   Maybe Jim would chime in if I'm not recalling correctly.

Bill

[Acer Saccharum]

I have no argument with your figures, BGF.

Bill D, that sounds awful low, 300 shots.

[Daryl]

The only vent hole fouling I get is with 2F fouling outside the barrel with my .40 and .45 only. When closing the frizzen, at times, a thin shaving of fouling will be scraped off the side barrel flat (top of the vent liner) & be pushed down over the vent hole upon closing, which results in a flash-in-the-pan.

Otherwise, unless dry balling, I've never had a flash in the pan with a WhiteLightening liner. It has however, happened to me with the screw or allen wrench'd vent holes due to excessive fouling in the 'works' (slots and wrench-hole), I suspect.

[Larry Pletcher]

It sounds like we're pretty much in agreement about what we like.  Give me a clean vent with barrel charge and priming practically touching, and I'm a happy camper.

In planning the testing, I can see couple of phases to try.  I mentioned earlier a web of .040" and .020".  I'd think it would be a good idea to time the straight 1/16" hole before starting to cut Tom's  internal shape.

I have another wrinkle to try but it may require a different barrel.  An ALR member who knows fluid dynamics mentioned to me that the quickest way to get air into a hole is with a horn-shaped entrance.  Think of the constant velocity stacks used on carbs on 60-70 hotrods.  (BTW our high school's Diesel car won the Shell Eco Marathon again using such an intake 1290mpg.)  Tom made me an external cutting tool to make such a vent entrance.  The problem is that such a entrance would gobble up a .020" web pretty quickly - hence the need to do this on another barrel. 

I don't mean for this last idea to be heresy; I just have this curiousity about what it would do. I'm plenty happy with the ignition I'm getting right now, but this constant velocity stack idea naggs at me to be timed.

Thanks for all your ideas.

Regards,
Pletch

[JB2]

hmmm...I was wondering about the same thing...were all vents flush with the barrel flat.  When were you planning this series of tests?

I have a barrel, not breeched yet ( I can do that), no touch hole, but it would be a 'stand-alone' series of tests.  It would have a very thick wall to work with (A-weight in .32 cal), so you could possibly combine horn-entry with internal coning (is that super-heresy?).  If no harm will come to the barrel, other than repairable touch hole mods, I might be up for volunteering it.

I just got a reply from Mr. Snyder about a coning tool that will fit into a .32 cal barrel, and he just made two last week!   Yep!

Well, this is exciting!

[Daryl]

 - If the rifle's best accuracy is desired, coning isn't.

[Acer Saccharum]

- If the rifle's best accuracy is desired, coning isn't.

This thread is about the internal touchhole cone, NOT the muzzle cone.