Coning flash hole liner

[Joe S]

Larry – I have an idea that may save some work milling the barrel:

Make a plug with the same thread as the white lightening, and a 0.062" hole, or whatever flash hole size you want to test. The initial length would be the same length as the maximum wall thickness that you want to test. After testing, remove the plug and shorten it to the next test length. You could do this a file and save the trouble of milling the barrel.

I don’t think it would be a problem if the plug initially intruded into the powder charge.

Speed is one thing, reliability is another. I have four flintlocks, a .54 and a 12 bore with white lightening vent liners, and two 10 bores with straight holes. The straight hole 10 bores are as fast and reliable as the white lightening liners, at least as far as I can tell. However, they have substantially larger flash holes. The flash holes in the white lightening liners are 0.062”. I started with 0.062“ holes in the 10 bores, but as I recall, the guns failed to fire at least half the time. I gradually enlarged the holes until I got reliable ignition at 0.081"

So, was the ignition speed of the 10 bores with a 0.062” flash hole the same as the speed with an 0.081” hole (that is, when the 0.062” hole managed to fire)? I have no idea, and I would not care to speculate, however, it seems possible that with thicker walled barrels, ignition speed may be a function of both barrel wall thickness and flash hole diameter.

The 10 bores are 1 1/4” at the breech, so 0.2375" wall thickness.
.

[Daryl]

Excellent idea on vent sizing and hole depth.  A large vent hole, so large it allows the powder close to the pan would of course, deliver virtually the same ignition speed.

2 problems with oversized vents, is pressure loss and also main powder charge loss if the hole is not plugged, or frizzen closed prior to shoving the ball down. The closed frizzen

was normal military loading sequence, but today, it frowned upon due to safety reasons.  Of course, to have a self-priming pan, an oversized vent hole is necessary, or extremely

fine powder, but also a closed frizzen.

[OldMtnMan]

There's a side effect for a big vent hole. Flintlocks have less velocity than a caplock. I assume that's because pressure is lost out the vent hole. The bigger the hole the more velocity lost.

Am I correct in this?

[Joe S]

Old MtnMan - I don't know anything about caplocks.

Daryl and Old MtnMan– I agree with you about safety issues with a self-priming gun, however I use 1F in my 10 bores. To get 1F to self-prime you would need an enormous hole.

Pressure is lost out of the vent, and, generally speaking, the bigger the hole, the more pressure that is lost. There is an anomaly, as noted. The easiest way to quantify pressure lost out of the vent is to measure projectile velocity. I have done some experiments with this. See:
http://americanlongrifles.org/forum/index.php?topic=32573.msg312716#msg312716

To summarize briefly, muzzle velocity increased when the flash hole was opened up from 0.062” to 0.067”, and thereafter decreased as hole size increased. The change from 0.062” to the maximum size tested (0.0995”) was relatively small, and would not have a significant impact on a hunting rifle. Perhaps a very high end bench shooter could detect a difference.

Here’s a table:



(Note to self – this table is not identical to the table in the link above, because the means for 0.062” were calculated from raw data, and means for other sizes were calculated from the regression equation.)

And here’s a graph:

[Larry Pletcher]

When I first saw this thread I knew I had an article on timing straight cylinder vents, but could not find it on my web site. I had to go back to old MuzzleBlasts copies to locate it.  I had to retype it, which is a struggle for me, but now have the text at the web link below. I'm having trouble locating the photos that accompanied the magazine article.  A summary chart will need to be redone, so it is still a work in progress.

https://www.blackpowdermag.com/touch-hole-ignition-timing/

Regards,
Pletch

[Dave R]

Jose,
Interesting date you have compiled in your testing!!
Possibly I overlooked it what caliber and barrel length are you testing to come up
with this data??

Thanks!!
Dave R

[Larry Pletcher]

After 19 years, I don't think I still have the barrel stub. I believe it was .50 or larger - seeing that we later used sabots in another test session.  It was probably 4-5 inches long. 

Regards,
Pletch

[Joe S]

Dave R – there is a fairly long discussion here: http://americanlongrifles.org/forum/index.php?topic=32573.msg312716#msg312716

The experiment conditions were: 

38” .50 caliber barrel (Getz)
70 grains Goex FF
Coned flash hole
15’ from muzzle to chronograph
Spit lubed 0.018” pillow ticking patch
0.495” Hornady ball
80 – 90 degrees F ambient temperature
Flat faced breech plug

[Daryl]

Accuracy comes from consistency. If the vent hole is large or small, but the velocities are within 10fps, the load has the potential to be more accurate than a load that
has 30fps spread, shot to shot.  The longer the range, the worse the potential accuracy will be for the load with more spread.
From here, we could get into shot to shot velocity variations and how they are caused & how they can reduced.

[MuskratMike]

Getting way way too complicated for this old man. Install Mr. Chambers White Lightning touch hole liner on all your guns you value. Fast, reliable, and last forever. End of subject.

[Daryl]

Getting way way too complicated for this old man. Install Mr. Chambers White Lightning touch hole liner on all your guns you value. Fast, reliable, and last forever. End of subject.

They do last a good spell. Only had to have 2 replaced so far. 

[Feltwad]

All I used in the 1970,s was a common Allen screw  with the rear end filed back leaving a 1/16 wall through which I drilled a 1/16 hole  re tempered and they are still going with no signs of ware , not fancy but they do the job with a quick ignition
Feltwad

Allen screw touch hole

[Daryl]

Is that a stub twist barrel, Feltwad?

[Feltwad]

Is that a stub twist barrel, Feltwad?

Daryl

Not a stub twist just a plain iron barrel.
Feltwad

[Flint62Smoothie]

Danny Caywood is the one who adds a large exterior cone to his touch holes and who is also vehemently opposed to liners ... his words, not mine.

[Dphariss]

I like liners, I never do an exterior cone.  I prefer to make my own liners.  Have had "issues" with store bought.  This will greatly reduce the pressure on the threads compared to other installations. All done with drills and a counter bore that makes a flat bottomed hole that is correct for 12x32. Liner is drilled a few thousandths less then the hole into the bore its about .100". Gotta do the measurements to get the counter bore in the liner the right length to get the charge close to the prime.















simple image uploader

This can be done a well. But requires the vent to be removed to debreech.... This was a rebarrel of the rifle with a low set lock position.

[Dphariss]

Old MtnMan - I don't know anything about caplocks.

Daryl and Old MtnMan– I agree with you about safety issues with a self-priming gun, however I use 1F in my 10 bores. To get 1F to self-prime you would need an enormous hole.

Pressure is lost out of the vent, and, generally speaking, the bigger the hole, the more pressure that is lost. There is an anomaly, as noted. The easiest way to quantify pressure lost out of the vent is to measure projectile velocity. I have done some experiments with this. See:
http://americanlongrifles.org/forum/index.php?topic=32573.msg312716#msg312716

To summarize briefly, muzzle velocity increased when the flash hole was opened up from 0.062” to 0.067”, and thereafter decreased as hole size increased. The change from 0.062” to the maximum size tested (0.0995”) was relatively small, and would not have a significant impact on a hunting rifle. Perhaps a very high end bench shooter could detect a difference.

(snip)

Was this a plain drilled vent or a liner with a counterbore?  I wonder if this would make a difference?
Interesting that the .067 gave higher velocity.  Just goes to show we don't know much about how a FL ignition system really works I guess.

Dan

[Dphariss]

Old MtnMan - I don't know anything about caplocks.

Daryl and Old MtnMan– I agree with you about safety issues with a self-priming gun, however I use 1F in my 10 bores. To get 1F to self-prime you would need an enormous hole.

Pressure is lost out of the vent, and, generally speaking, the bigger the hole, the more pressure that is lost. There is an anomaly, as noted. The easiest way to quantify pressure lost out of the vent is to measure projectile velocity. I have done some experiments with this. See:
http://americanlongrifles.org/forum/index.php?topic=32573.msg312716#msg312716

To summarize briefly, muzzle velocity increased when the flash hole was opened up from 0.062” to 0.067”, and thereafter decreased as hole size increased. The change from 0.062” to the maximum size tested (0.0995”) was relatively small, and would not have a significant impact on a hunting rifle. Perhaps a very high end bench shooter could detect a difference.

(snip)

What happened to the velocity standard deviation? Testing has shown that accuracy suffers with vents much larger than .062...
Dan

[Joe S]

Good questions Dan.

Was this a plain drilled vent or a liner with a counterbore? 

There is no counterbore. We could test this hypothesis, after turkey season.

What happened to the velocity standard deviation? Testing has shown that accuracy suffers with vents much larger than .062...

In the test data posted above, there are not enough data to say anything definitive about the standard deviation. However, I checked my notes and found that I had looked at this too. I’m getting too old – I had completely forgotten about that test….

The question of standard deviation was tested for 0.062” and 0.0995” flash holes. The average velocities were 1522 and 1417 FPS, and the standard deviations were 30 and 48 FPS, respectively. The difference in the standard deviations was statistically significant, so we can say with some confidence that variability really does increase when you change the flash hole from 0.062” and 0.0995”.

Here’s the data:

[Skirmisher]

For whatever little bit of good this does....  I have a sizable number of original flintlock guns.  A few have original touchholes in unaltered condition, and it seems that they were generally drilled at a forward angle, then reamed to form a long cone.  Don't know how this helps the modern enthusiast but this seems to have been the preferred approach in the days before touch hole liners were common except on fine fowlers.