touch hole: how big is too big?

[Larry Akers]

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

You and I are on the same wavelength. The delay is less with a small touch hole. Mine are less than .060". Report what you experience--we'd be interested.

To Sence: the reason is that most of the gas that escapes thru a large TH is contained in the gun by a small TH where it can do work (move the ball).

 

[Grenadier1758]

There are 5 numbered drill sizes between 1/16" and 5/54".

1/16 0.0625
52 0.0635
51 0.0670
50 0.0700
49 0.0730
48 0.0760
5/64 0.0781


Many of us with numbered drill bits use either the 51 or the 50.

 

[Billnpatti]

Getting the size of the touch hole just right is a balancing act. Too small and the flash has a hard time getting to the main charge. This means irregular ignitions and flash in the pan problems. Too large and you start to loose breach pressure. This can result in irregular breach pressures which translates into irregular muzzle velocities and this means a loss in accuracy.

The White Lightning touch hole liners come with a pretty tiny hole. For best ignition, this hole needs to be enlarged to about 1/16 inch. Some folks will go a few thousandths larger than 1/16 inch but not much. If you have not enlarged your touch hole, that is likely part of your problem. secondly, you need to make sure that the touch hole is properly located at the "sunset" position. That is, it needs to be centered on the pan and located just at the top of the pan. The term "sunset" position is used because a properly located touch hole looks like a setting sun on the horizon.

With the hole properly located and at least 1/16 inch in diameter, you can make one more improvement on it if you have 3 things...(1) A Dremmel tool, (2) a small fine pink ball shaped grinding bit for your Dremmel and not the least is (3) a steady hand. If you have these three things, you can carefully add a shallow cone to the outside of your touch hole. Coning your touch hole will help direct the flash into the main charge. You didn't mention the caliber of your gun but using 3f as your main charge will help with the ignition as well. I know that the "old folks" will say that you need to use 2f for calibers greater than .50. "Tain't so. 3f will work fine in the larger calibers if you just reduce the charge by about 10%. It burns cleaner, too, and leaves less fouling in your bore. However, I do use 2f in my shotguns and large caliber smoothbores. I could probably use 3f in them, too, but I just choose not to. Am I right or wrong in doing so?....Can't say. :idunno: It's just what I do. :wink:

 

[George]

Too large and you start to loose breach pressure. This can result in irregular breach pressures which translates into irregular muzzle velocities and this means a loss in accuracy.

I know that's the idea, but I don't buy it. I can't think of any reason pressure would be variable because of the size of the hole. Can you?

Spence

 

[George]

To Sence: the reason is that most of the gas that escapes thru a large TH is contained in the gun by a small TH where it can do work (move the ball).

But it escapes the same every time if the charge remains the same. So, it might change once, when you enlarge the hole, but would be the same every shot after that. All you have to do to prevent any change in the trajectory is add enough powder to the charge to compensate for the increased loss.

Spence

 

[Larry Pletcher]

There are 5 numbered drill sizes between 1/16" and 5/54".

1/16 0.0625
52 0.0635
51 0.0670
50 0.0700
49 0.0730
48 0.0760
5/64 0.0781


Many of us with numbered drill bits use either the 51 or the 50.

Here, here. You beat me to it.
Pletch

 

[Billnpatti]

Too large and you start to loose breach pressure. This can result in irregular breach pressures which translates into irregular muzzle velocities and this means a loss in accuracy.

I know that's the idea, but I don't buy it. I can't think of any reason pressure would be variable because of the size of the hole. Can you?

Spence

Agreed that in an ideal condition where everything remains constant, the size of the hole should make no difference in the variation of the breach pressures. However, in the real world, it appears to make a difference. That is why when a touch hole is eroded to a larger size, it is usually replaced to regain the lost accuracy. I guess there are obviously variables in the real world that are not in the text books.

Let me add this disclaimer....I do not hold myself out to be an expert in muzzleloading, ballistics, thermodynamics, fluid mechanics, etc. I've just been shooting for several years and can only state my personal experience and tell of reports of others whom I trust. Beyond that, I'm just an old fart with opinions and ideas, some of which may hold a modicum of value and some of which are but a fart in the wind. :haha: I'll lay them out there and you sort them into either the keep or reject pile. Either way, I will be your friend. :thumbsup:

 

[George]

I guess there are obviously variables in the real world that are not in the text books.

Ah, the old magical variable ploy. Which explains nothing, but is a perennial favorite. :haha:

Either way, I will be your friend. :thumbsup:

We aren't talking about friendships. Friends can disagree and still be friends. On second thought, that's a value carried over from another world and seems not to be applicable in today's world. I don't want to be considered old fashioned, so disregard, and watch your step. :haha: :haha:

Spence

 

[Larry Akers]

Spence, what you say is true but BJ is not talking about muzzle velocity or trajectory. He's talking about the time between sear-trip and the rifle going "bang"--barrel-time if you will.

Assume all things are equal except TH size. There is a minimum pressure that must be present in the breech to start the ball moving. This minimum pressure is achieved in less time with a small TH than with a large TH because of less pressure loss. Therefore there will be less "barrel-time" with the small hole because the ball will begin moving sooner and will accelerate faster.

 

[Billnpatti]

As you said " Ah, the old magical variable ploy. Which explains nothing, but is a perennial favorite. " To which I reply "There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy."-Shakespeare.

It reminds me of the cartoon where a professor is standing in front of a blackboard that is covered with equations and the final note says "And then a miracle happens" :rotf:

 

[Maven]

Spence & Bill, I own a Green River Forge 20ga. trade gun whose touch hole had seen better days. It also misfired frequently enough for me to replace the vent with a White Lightnin' vent liner, it didn't improve reliability until I enlarged the new flash hole. Unfortunately, I enlarged it so much that it would easily accept a 14 ga. (?) copper wire [from Romex cable]. In fact, I had to keep that wire in place or it would spew 2Fg powder into the pan while loading the piece. Despite that absolutely huge vent hole, I saw no diminution of accuracy or reliability. Indeed, the gun rarely misfired. You wouldn't want to be standing nearby (on the right) when I fired it though!

Several months ago I got enough nerve to change out the replacement White Lightnin' with a new one and "machined' some of the intruding breech face with a milling bit in my Dremel motor tool handpiece. I also opened the touch hole to 1/16". I'm happy to report the trade gun is now reliable and accurate enough to make it enjoyable to shoot. In short, my experience is congruent with what Spence wrote the other day.

 

[Billnpatti]

Whaaaat???? Spence was right?????? Miracles still happen. :rotf:

Love ya, Spence :grin:

 

[Black Jaque Janaviac]

Spence, I agree that an enlarged vent should not affect the bench accuracy but I believe it could affect your offhand accuracy.

The time it takes between tripping the trigger and the ball exiting the muzzle can be broken into two events, lock time and barrel time. Lock time begins with the trigger tripping and ends the moment the main charge begins to burn. Barrel time begins where lock time quits and ends when the ball leaves the muzzle.

An enlarged flash hole may speed up the lock time, but I am guessing the law of diminishing returns kicks in and at some point the barrel time would increase. The reason for this would be because the pressure needs to build up to a certain point in order to overcome the inertia of the ball. The time it takes for the pressure to reach this critical point will be slowed if too much gas is being released out the vent. My guess is that there is an optimum touch hole size for a given gun/load that will yield the shortest combined lock time and barrel time.

The fact that when I fired my gun without a ball and did not get a perceptible delay between trigger trip and muzzle report, whereas I do get a noticeable delay when the powder has to work at expelling a ball, tells me that my barrel time is too long.

 

[azmntman]

you old guys are almost always right...even when you disagree, yer both right? Right? Ahh what we can learn while having fun!! :hatsoff:

 

[excess650]

Following the "barrel time" logic would suggest that shooters with short barreled rifles would fare better than those with long barrels for offhand work. Is that what is observed in match shooting?

My 28-1/2" barreled .62 seems to have the quickest ignition/report of my (4) flintlocks, and it also has the smallest touch hole.

Muzzle velocity from my 42" .50 should be considerably higher than that from the .62, so "barrel time" should be similar, yet I perceive a longer ignition/report from that .50, and likewise my 38" .45.

I shoot that long barreled .50 best offhand.

 

[hanshi]

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

I got beat to it but yes, ignition is when the gun goes bang; or, more strictly, when the main charge ignites.

 

[George]

Spence, I agree that an enlarged vent should not affect the bench accuracy but I believe it could affect your offhand accuracy.

In these discussions, whenever the question of accuracy comes up, we can wind up talking about two very different things, gun accuracy and shooter accuracy. It's not uncommon for me to be talking about one, someone else taking about the other, and we neither realize what's happening.

I am usually talking about gun accuracy, what the gun is capable of at its best, no shooter input. That has always seemed very important to me, because if we don't get the gun shooting at its very best as a first move, then the shooter can't do his best.

In the present discussion, I agree with the general description of lock time and barrel time, but I'm thinking about gun accuracy, not shooter accuracy. I don't believe an enlarged touchhole which causes a delay in the ball starting to move, which it could do, and an increased barrel time will do harm to the accuracy of the gun. That is very much dependent on the consistency of muzzle velocity. Same velocity equals same trajectory equals same accuracy, and it doesn't really matter what happens before the ball leaves the muzzle so long as that velocity is the same. It may not be the same when considering guns with small and large touchholes, but it will be the same for each, so long as all else is equal.

On the other hand, shooters can certainly be put off their best performance by any significant delays in the firing sequence. Not all of us have a perfect followthrough, which would cancel out those little problems, and so we degrade the accuracy which the gun is capable of. And, of course, blame it on any other convenient thing. :wink:

Spence

 

[Stumpkiller]

Can I say why a larger vent causes inconsistent pressures? No.

Can I say target shooters claim it does cause wider variations in muzzle velocity? Yes.

Can I say they are using 5/32" or larger vents to guarantee reliable ignition because it does not matter. No.

Can I say most I know like to keep around a 1/16" vent because they claim it gives more consistent results? Yes.

I have no way to measure pressure, velocity or lock time. My Bess didn't have a liner and the vent was 7/64". Went off every time and seemed to be fast ignition. Not quite big enough to clean out with my pinky but noticeably large.

Both my current flintlocks are 1/16" and nicely reliable.

 

[Don Steele]

Excess650, to respond to your question I can only offer my personal observation of the only collected group of SERIOUS offhand muzzleloader shooters I've ever been around.
That would be the competitors at Friendship during the National Matches.
Recently, while discussing some possibilities for "my next rifle"..I had commented to some of my shooting buddies that when I walk the offhand line at Friendship, there seems to be a lack of the very traditional, very HC longrifles among those shooters who specialize in the offhand target game. I see a lot of shorter, heavier barrels, not the long slender barreled "squirrel rifle" styles.

 

[Billnpatti]

AMEN!! Spence......testify, brother, testify!! :bow: I am in complete agreement with you.

Having said that, and I do fully agree with what you are saying, let me toss this idea out for your consideration....do you think variations in charge will effect barrel harmonics on the average longrifle? If so, will it be enough to amount to a factor in gun accuracy? My inquiring mind wants to know. My guess, and it is just a guess (a WAG, not even a SWAG), is that in the average longrifle, barrel harmonics will not be an accuracy factor. But, I have been wrong before. I remember back in 1957 I was standing at attention at MCRD is San Diego and my DI tenderly pointed out that somehow I had, with malice aforethought, been wrong. I think it was my breathing wasn't to Marine Corps standards or perhaps my eyes didn't click when he said "Eyes right" The exact error is lost to me among a plethora of other errors that I carelessly committed. What I do clearly remember is a lot of yelling and a strong cigarette breath and a voice in the back of my head saying "I want my Mama."....... :haha: