Vent Coning Question?

[davec2]

Having read the recent posts about using a liner in the vent or not, and about coning the vent from the inside, were not the vents of some  original English guns coned from the outside?  I seem to remember some pictures posted on the old board of a high end Englisg gun in pristine condition with what looked to be a very large vent.  But I think someone mentioned that the vent was coned from the outside.  Does it make a difference if a vent is coned from one side or the other?  Perhaps more work for Larry Pletcher and his high speed camera?

[J. Talbert]

Dave,

I don't have any scientific comparisons, but my experience has led me to prefer the "coned from the inside" option.  In addition to years of good results using this type of vent liner, it's also my theory that the smooth cone on the inside of the vent focuses the pressure from the burning powder and cleans the touch hole with each shoot.
Years of reliable ignition despite my personal shooting habits of not cleaning and not picking the vent between shots, has lead me  to this conclusion.

Perhaps your expertise could shed some light or throw cold water on my theory.

Jeff

[Pete G.]

Just to muddy the waters a bit, Danny Caywood cones his from the outside, claiming it is the historically correct method.
Although I have never tried the outside cone, my logic and engineering background leads me to Jim Chambers' White Lightening for a shooter. One day I aim to try a drilled vent, and if not satisfied, I can allways drill it out and install a liner.

Liners may not be historically correct, but neither are machined barrels, castings for lock plates, cast springs, die cut inlays............and the list goes on.

[Dphariss]

Large external cones are not reliable.

Dan

[davec2]

Jeff,

I really have not idea about which way might be better.  However, in a rocket nozzle, hot gas directed into a De Laval nozzle will accelerate in the converging section and reach sonic velocity (i.e. Mach 1) at the throat (minimum diameter).  The only way to accelerate the gas to higher than sonic velocities is to allow it to expand inside a divergent section.  The gas can then reach super sonic velocities.  To relate this to a vent liner, with an inside cone, the "throat" is at the outer wall of the barrel and the gas escaping can only reach sonic speed.  On the other hand, if the vent is coned from the outside, the escaping gas can reach much higher velocities.  If the scrubbing action of high velocity gas is what keeps the vent clean on its own, the outside cone may work better.

Now what the $#*! all of this has to do with the reality of shooting a rifle with an inside or an outside cone (or no cone) on the vent is anyone's guess.  I just thought someone out there might have some practical, first hand experience with outside cones.  It is certainly a heck of a lot easier to cone the vent from the outside.

[davec2]

Dan,

Unreliable how?  Shot to shot velocity differences? Accuracy? Ignition?

Thanks

[Don Getz]

Another bit of wisdom from the Caywood clan,.........mythology at its best.........Don

[Stophel]

I have a picture of a pistol with a copper-colored bushing that APPEARS to be an outside cone (it's a pretty big hole, and still nice and clean and round, so I don't think it's worn to that size).  Other than that, I have yet to see or hear of an old gun with an outside coned touch hole.

It's so easy to do an inside cone, there's no real reason to do it any other way.

[MikeC]

I have owned both and currently only own firelocks with liners, and that is the way all future builds will be.

[J. Talbert]

Well Dave,
Perhaps my theory on the self cleaning properties of an inside cone are all wet, even though it seems counter intuitive.
At any rate... I've been quite satisfied with the result this long so I guess I'll stick with it.  Besides, I now have the clever little tool that will allow me to cone from the inside and should give the same result while retaining the traditional look.

Jeff

[Dphariss]

Dan,

Unreliable how?  Shot to shot velocity differences? Accuracy? Ignition?

Thanks

I suppose large is a relative thing. But in my experience the exterior cone tends to foul and the escaping gases don't clean it. This will result in flashes in the pan. I assume the fouling buildup somehow insulates the main charge from the flash (?)
But I have never tried one with a really deep large cone and won't.
Most of the research into fast and reliable flintlocks took place in England prior to 1820. They settled on a vent liner remarkably like  the White Lightning for the high end guns. Though they were platinum lined and not stainless. But stainless is ballpark for color.


This liner is surely platinum lined.



The bottom is in a rifle I built to hunt with. When loaded the powder in the vent is within .020 of the pan.
It never fails to fire if clean and never fails dirty unless a flake of powder fouling blocks the interior of the vent which happens very rarely.
So it is very consistent.
The pan cover on the frizzen wipes the exterior clean.
It is the best vent design I have ever used. The conical interior featured in the WL is not absolutely needed and a simple drilled interior counterbore will work and can leave a thicker wall over the threads. (I think Larry Pletcher's tessting show the speed of the two types to be pretty close with the WL the fastest). So long as powder can enter and get to the restriction it will be sure fire. The drilled counterbore will allow reliable vent liners down to 10-32 thread to be made. The smaller diameter can help with clearance problems at times.

 I make them both ways and have used a WL and I have a WL I will be installing in a barrel for a friend in the next couple of days. Using the WL (I prefer the smaller diameter ones) allows easy replacement if it becomes enlarged with use. But the rifle above now has a shop made version since it required replacement and I could make one faster than the mail could get a WL  here. Its nearly identical just has a smaller cavity. I have a lot of scrap stainless around so I have stuff to make it from.
Over the years I used a great many different vents from plain 3/32" drilled ones to WL. Unless very poorly designed a vent liner is better than a drilled vent in every way.

Dan

[Roger Fisher]

Dan,

Unreliable how?  Shot to shot velocity differences? Accuracy? Ignition?

Thanks

I suppose large is a relative thing. But in my experience the exterior cone tends to foul and the escaping gases don't clean it. This will result in flashes in the pan. I assume the fouling buildup somehow insulates the main charge from the flash (?)
But I have never tried one with a really deep large cone and won't.
Most of the research into fast and reliable flintlocks took place in England prior to 1820. They settled on a vent liner remarkably like  the White Lightning for the high end guns. Though they were platinum lined and not stainless. But stainless is ballpark for color.


This liner is surely platinum lined.



The bottom is in a rifle I built to hunt with. When loaded the powder in the vent is within .020 of the pan.
It never fails to fire if clean and never fails dirty unless a flake of powder fouling blocks the interior of the vent which happens very rarely.
So it is very consistent.
The pan cover on the frizzen wipes the exterior clean.
It is the best vent design I have ever used. The conical interior featured in the WL is not absolutely needed and a simple drilled interior counterbore will work and can leave a thicker wall over the threads. (I think Larry Pletcher's tessting show the speed of the two types to be pretty close with the WL the fastest). So long as powder can enter and get to the restriction it will be sure fire. The drilled counterbore will allow reliable vent liners down to 10-32 thread to be made. The smaller diameter can help with clearance problems at times.

 I make them both ways and have used a WL and I have a WL I will be installing in a barrel for a friend in the next couple of days. Using the WL (I prefer the smaller diameter ones) allows easy replacement if it becomes enlarged with use. But the rifle above now has a shop made version since it required replacement and I could make one faster than the mail could get a WL  here. Its nearly identical just has a smaller cavity. I have a lot of scrap stainless around so I have stuff to make it from.
Over the years I used a great many different vents from plain 3/32" drilled ones to WL. Unless very poorly designed a vent liner is better than a drilled vent in every way.

Dan

Ok I'll be the 'one' to ask   I notice that the vent is a tad forward of center of the pan on that double or is that one of my optical 'delusions' that I get at times??
Am very glad to see your statement that the ignition is just fine in that setup, since my last effort came out similar on a smoothbore!

[davec2]

Dan,

Thanks for the response - great pictures.

Dave C

[Dphariss]

Ok I'll be the 'one' to ask   I notice that the vent is a tad forward of center of the pan on that double or is that one of my optical 'delusions' that I get at times??
Am very glad to see your statement that the ignition is just fine in that setup, since my last effort came out similar on a smoothbore!

The rifle is off center. I built the breech complete before inletting the lock and was a little "off" when I was done.
The Manton double is likely a optical illusion. But it could be off too. Next time I am in the Cody Firearms Museum I will try to get a better photo, if I don't forget.

Dan

[t.caster]

I've tried it both ways at the behest of other members of our gunsmithing guild, (20 yrs. ago) who thought outside coning was the catsmeow. I switched my perfectly fine inny to an outy, in the form of a sst socket set screw w/.062 dia. hole drilled on center. After only one shoot, I switched back because of constant hangfires or just slower ignition. Yes, it was noticeably slower! Two of the guys still use the outer coned liner today. It's OK by me, if they want to handicap themselves.

[Jimmy82]

Wouldn't faster escaping gases cause more pressure loss also?  So while an outer cone might potentially self clean better you are sacrificing pressure value and consistency.  At least that's how I understand it.  I could imagine that an inner cone might even help boost pressure over a straight drilled hole.  Having a space suddenly constrict would create a pressure pocket that could help act as a speed break for escaping gases.  Thus more pressure is retained in the barrel and returned by either increased or more consistent muzzle velocity.

Of the originals I have seen, all were either straight hole or inner cone, can't tell more precisely because they were museum pieces.  They had to do it for a reason and while the backwoods gunsmiths might not have had solid math or science skills the big name companies sure would have some egg heads in the back room trying to figure out ways to improve performance.  Once the big companies did it, it would all trickle down until it was industry standard.

Now think about this.  If the outer cone increases the speed of gases coming out of the barrel after main charge ignition, wouldn't an inner cone speed the gases coming off of the priming charge thus creating faster ignition speed?  While we're not talking anywhere near the pressures that occur inside the barrel, rapidly heating and expanding gases all follow the same laws of physics.  By this logic an inner cone should be the most preferred.  Not only is the powder closer to the flash, but the flash moves faster towards the powder.

[Acer Saccharum]

Nock did something like this for his cones:



Cone the barrel from the opposite side.

I don't see why you couldn't use it for a contemporary flinter. Just make sure your machining is good.

[Dphariss]

Gases do not enter the vent the pressure is not high enough when the gun is *loaded*, just radiant heat and maybe an random spark/flaming powder granule.
Gases, fouling etc from the priming WILL enter the vent of an empty gun.

Dan

[Larry Pletcher]

In Feb 2000 issue of MB I did a test of straight cylinder vent holes.  Many  test sections have no bearing here but one test may be relative.  In timing a 1/16" (straight cylinder) hole, I first ran 20 trials normally and then did an exterior cone and retimed it.  The cone was fairly small, but there was a difference.  Here is the number comparison:

                1/16" no cone       1/16" w cone

average:  .044--------------------------.0406
st dev.     .00830-----------------------.00834
variation: .0321-------------------------.0278

In 2000 when I wrote the article, I decided that if I built a rifle without a liner the vent would be at least 1/16" and it would have an exterior cone.
Regards,
Pletch

[Jimmy82]

Gases do not enter the vent the pressure is not high enough when the gun is *loaded*, just radiant heat and maybe an random spark/flaming powder granule.
Gases, fouling etc from the priming WILL enter the vent of an empty gun.

Dan

What about when you create a channel in the powder from poking it with the pick?  Some gases have to enter, but the cooler air that is still in the barrel would be more dense then the gases coming off the flash, so yeah.  It is probably such a small amount that it is unmeasurable and not enough to really make a difference.  But it was fun to think about.

[Dphariss]

The barrel is sealed by the load.
Pressurizing invading the vent would require more pressure than a small amount of powder can generate since it must compress the air already there.

Dan

[Dphariss]

In Feb 2000 issue of MB I did a test of straight cylinder vent holes.  Many  test sections have no bearing here but one test may be relative.  In timing a 1/16" (straight cylinder) hole, I first ran 20 trials normally and then did an exterior cone and retimed it.  The cone was fairly small, but there was a difference.  Here is the number comparison:

                1/16" no cone       1/16" w cone

average:  .044--------------------------.0406
st dev.     .00830-----------------------.00834
variation: .0321-------------------------.0278

In 2000 when I wrote the article, I decided that if I built a rifle without a liner the vent would be at least 1/16" and it would have an exterior cone.
Regards,
Pletch

My concern is reliability. I have owned several guns with liners with inner counterbore and small outer cone. I got unexplainable flashes in the pan with them. One at a MD buck with a clean gun. I also noticed less than ideal performance when shooting a long string of shots.
The White Lightening/British type or similar (inner counterbore rather than a cone) but flat at the pan end with a short 1/16"+- vent to the inner cone/counterbore has proven to be the most reliable for me.

Dan

[Larry Pletcher]

Dan,
You may be correct about reliability.  I cleaned religiously between shots in my timing because I did NOT want fouling to be a variable.  Because of that I encountered no reliability issues.  In a world outside of lab conditions, I have no data, so I won't offer speculation.
 
I might add that the rifle I currently shoot has a Chambers liner that functions nicely.  I should also say that in 2000 when I wrote the article I wanted it to be a base line for future comparisons with liners.  I guess that my use of WL liners speaks to my opinion of that comparison.

Tuesday I shot the woods walk at friendship with the rifle mentioned above.  I carry a pipe cleaner because of my opinions about fouling.  Because the liner functioned so well, I forgot all about the pipe cleaner - never used it once.  And I used Rich's flints - also worked flawlessly.

Regards,
Pletch

[davec2]

Thanks to all for the responses.  I believe that the preponderance of evidence suggests that the inside cone is the correct answer - rocket nozzle theory aside.

To Jimmy82:  The increased gas velocity in the diverging section of a De Laval nozzle (I.e. in this case, an outside cone) is the result of physically allowing the gas to expand.  Since the throat is sonic, that is choked, it would have no effect on the pressure in the barrel.  Secondly, the process does not work in reverse for an inside cone because the external pressure at the vent is 1 atmosphere (~14.7 psi) which is not sufficient to cause choked flow (as Dan correctly implies in his response).

Larry:  Thanks for the data.  I think Dan is also correct about the vent with an outside cone fouling more than an inside one.  I thought you might have hard data to look at.

[Jimmy82]

Learn something new everyday    Thanks for breaking it down or I would have continued to be ignorant.  I'll probably be replacing some vent liners...  I don't suffer many misfires but every little bit helps.

If I may, for the sake of general knowledge, what shape would be best for the inner cone?  Straight cone or a more parabolic curve?