touch hole: how big is too big?

[Black Jaque Janaviac]

What happens when a touch hole gets too big? Can it delay the shot?

I am in the process of replacing a 15 year old White Lightning liner. My gun has been puzzling me for some time now because there seems to be a perceptible delay when firing.

I thought it was the lock and polished that up real nice. But no joy.

I opened the hole up with a #50 bit. I noticed that the hole did not appear perfectly round before drilling. The oblongn shape may be due to the piano wire pick I had been using to clear the hole. I thinknthe wire eroded the hole.

Some other things that cause me to think the ignition delay is due to an enlarged hole:
The delay is only perceptible with a real charge. I do not notice the delay when merely putting some powder down bore (no ball).

I do occasionally see specs of 2f that leaked onto the pan during loading.

I am thinking that the main charge ignites plenty quickly, it is just that with a larger hole too much gas leaks out before the pressure builds up to make the boom. That would explain why there is no delay when there is only powder and no ball since the pressure does not need to build up as much.

Anyone else have a similar experience?

 

[Stringbean]

I don't think .070" is overly large although I wouldn't go much larger. In my experience, a larger thouch hole makes for faster ingition. Try firing it a few times without picking the vent. My rifles don't like to be picked.
String

 

[ohio ramrod]

While some go as large as 5/64. The Bevel Brothers did some serious testing some years back and concluded that 1/16 was the best all round size. For sure ignition and best groups. Larger flash holes improve reliable ignition but due to more gas escaping enlarges groups. :idunno:

 

[Larry Pletcher]

IMHO if you need to go to .070 or bigger, there is a bigger ignition problem to find. Of course that opinion and 50 cents used to buy you a coke. Not sure lately.
Regards,
Pletch

 

[Black Jaque Janaviac]

Well the problem wasn't unreliable ignition. With the .070" hole there were no failure to fires. Just a barely perceptable hesitation between the lock going off and the rifle's report.

 

[George]

Larger flash holes improve reliable ignition but due to more gas escaping enlarges groups. :idunno:

I don't know of any reason that should make a gun shoot larger groups. It could cause a shooter to do so, if it caused a delay and he didn't have a good followthrough. I have an old original smooth rifle with a fairly large and burned touchhole, and it shoots as well as my modern one, I don't notice a delay.

In my experience, if a touchhole is burned and larger, you can compensate for the extra gas loss by increasing the charge a little. The larger touchhole allows a loss of pressure, but the extra powder increases it, so the net result is no loss of effective pressure and velocity.

Spence

 

[Black Jaque Janaviac]

So the question is, does larger vent cause a delay in building up to that pressure?

 

[Stringbean]

for all practical purposes: No

 

[Larry Akers]

For me, my touch hole is too big if grains of powder (3F) exit the hole during loading. But then, I like a smaller touch hole than most on this forum. Go ahead and put in a new liner (don't enlarge the hole) and you will be amazed how much faster your ignition is. Only enlarge the hole if ignition is unreliable and then only to the point of reliability.

 

[excess650]

For me, my touch hole is too big if grains of powder (3F) exit the hole during loading. But then, I like a smaller touch hole than most on this forum. Go ahead and put in a new liner (don't enlarge the hole) and you will be amazed how much faster your ignition is. Only enlarge the hole if ignition is unreliable and then only to the point of reliability.

I agree. My quickest ignition is with my smallest flash hole, and it is less than .060". I experimented with enlarging and external coning on a troublesome rifle; when I sorted its problem out, I replaced the too large(at that point) liner with a new one with 1/16" hole.

 

[Vaino]

If a larger than say a .067 TH dia. {#51 drill} is req'd for reliable or quicker ignition. then something else is causing the 2 above ignition problems.

If the ignited prime has to "go through tunnels" as in the variations of different patent breeches, the speed of ignition might be slower or a longer TH as in the absence of a proper liner, the prime might ignite a "fuse" and cause an ignition delay.

When I first shot a build w/ a "White Lightning" TH liner, the thought struck me that the fun of shooting a flintlock was gone.....the ignition was too fast being comparable to a caplock.... previously I had gotten used to a slight delay which req'd follow through.....Fred

 

[excess650]

My "troublesome flintlock" has the liner too close to the breechplug, and while the TH was at the desired height, it was offset in the pan. After enlarging and coning the exterior of the liner with minimal improvement, I decided to widen the pan so the TH was more centered. The latter helped immensely, so when the liner was replaced (dribbled fffg), I slightly relieved the face of the breechplug. With a 1/16" TH, it is much improved. I'm thinking of deepening the pan under the TH so that the prime is further below.

 

[Danny Ross]

It maybe psychological. You THINK after the ignition of the charge the time the round ball exits the barrel is longer when it is not. The larger flash hole may let a little more gas escape giving the ball a little less FPS but I would not think it would be perceptible to a human. As an example the difference of 70 grs of powder and 90grs of powder, no human can tell the difference of how fast the ball exits the barrel with the two different powder charges. The other possibility is if you are swabbing between shots there maybe some moisture in the barrel, dampening the powder, causing a delay of the powder burn, slowing the build up of pressure for the ball to exit the barrel. The reason I say this is because you say you have no perceived delay when no ball is used. DANNY

 

[Black Hand]

Too large is when your main charge pours out almost as quickly as it went int...

 

[Larry Akers]

It maybe psychological. You THINK after the ignition of the charge the time the round ball exits the barrel is longer when it is not. The larger flash hole may let a little more gas escape giving the ball a little less FPS but I would not think it would be perceptible to a human. DANNY

Changing from a large to a small touch hole there is a definite difference in time between sear release and the gun saying "Bang" ( has nothing to do with velocity) . This may not be noticible to a bystander but would be very obvious to the shooter who is accustomed to the gun whose touch hole has enlarged over time. This difference could be the difference between a 9 or 10 and a 7 or 8 on a target, or a heart-lung shot vs a gut shot on an animal. The faster the gun says "bang" the more accurate it can be shot. If I am aware of hearing any fftt when my gun fires, I start thinking of changing my liner because my ignition time has slowed.

 

[hanshi]

I don't see how an enlarged touch hole can cause slow ignition. If anything, it "should" be faster. I settled on a 1/16" touch hole for all my guns and they all sound instantaneous to me. It helps that I prime with 4F. Still, if I slap the off side of the lock plate, frequently a few undersized kernels of 3F get into the pan. This is how I assure myself the vent area isn't plugged with fouling.

 

[Larry Akers]

We may be having a semantics problem on this thread. Define "Ignition"

 

[George]

Changing from a large to a small touch hole there is a definite difference in time between sear release and the gun saying "Bang" ( has nothing to do with velocity).

What would be the reason for that?

Spence

 

[Black Jaque Janaviac]

I agree that there is a semantics problem. I am not sure how to describe it other than to use the word "report" to referr to the sound of the muzzle blast. This is to distinguish from the actual ignition.

Perhaps the best way to describe my problem would be to say that there is a delay between ignition and report (muzzle blast).

Once the mercury climbs back up and I have some time to play, I will try my gun with a new touch hole and see if the problem is solved.

 

[TerryK]

I just drilled out a 1/16 to 5/64. The difference in diameter looks huge. I did not test it yet, but I have a standard 1/16 to revert to in case it does not work well. If I were to do it again, I would look for a smaller drill bit or just move the 1/16 bit in the hole a bit. Anyway 5/64 looks huge.