ideal flash hole size

[yip]

 i installed a white lighting liner, the hole a little high,but the size of the flash hole itself seems a little small, i'm thinking it should be 1/16th". any thoughts?

[chrisdefrance]

Take some time and look at past posts that have been completed as titled below. In the Tutorials there are a number of Articles from BlackPowderMag and written by Larry Pletcher. These are exceptional studies of the flintlock. You should find exactly what you are looking for.

BlackPowderMag  Posted by: Larry Pletcher       Lock Timing, Lock Tuning, Lock Filming

These are the most complete film/time studies done on the flintlock that you can find anywhere.
Thanks to Larry Pletcher and BlackPowderMag.

[Pete G.]

They are small as manufactured; intentionally made that way.
Drill out to .0625" and put a light chamfer on the outside.

[Joe S]

I actually have some data on this question that I’ll post as soon as I get it written up.  The first issue is reliability of ignition.  As Pete G stated, 0.062” is a good size.  The general experience with the White Lightening seems to be that 0.062” is about the smallest flash hole that will give you reliable ignition.

For what it’s worth, I have a White Lightening with a 0.062” flash hole in a .54 rifle.  I shoot a fair amount, and I don’t recall ever having a flash in the pan.  I also don’t pick the flash hole, or clean between shots.

[wattlebuster]

All of mine shoot good with a 1/16th hole

[Ray Barbarow]

I always start with the .055" touch hole as manufactured and shoot the rifle to determine if I have reliable ignition. I re-barreled my rifle two years ago and never opened the touch hole beyond its original diameter. I now have slightly over 1900 rounds through the barrel and the same touch hole is still installed. The next larger number drill is .059" and it will not pass through the touch hole. I have no misfire problems. Yip you have seen how reliable my rifle is. This will vary from one rifle to another. Shoot it and see how it preforms before you put a drill to it.

[Dave R]

Anybody think the design of the pan has anything to do with reliable main charge powder going off with lets say a .055" white lightning touchhole? Vs a .0625 or a little larger both with chamfer?

[Joe S]

I don’t know of any data on the reliability of ignition as a function of flash hole size.  I’ve thought about doing that experiment, but you are talking about many hundreds of shot to get reliable data.

Lots of folks shoot white lightening liners with a 0.055” flash hole.  0.062” is a size that people have converged on based on experience, but, like I said, I don’t know of anyone who has actually recorded any data.

Also, I don’t know of any data that addresses the effect of chamfer on reliability. Pletcher’s experiments showed it has no effect on speed of ignition.

Pletcher’s data suggest that a pan that was designed to keep the charge close to barrel might increase reliability of ignition, but that’s a bit of a stretch.  He was actually measuring time to ignition, not reliability.

So, Dave, a wide open field here for experimentation.

[RAT]

My personal opinion is that the 1/16" hole was generally accepted because of the universal availability of 1/16" drill bits. The next numbered drill size above or below this probably makes little difference, but are harder to find at your local hardware store.

[Larry Pletcher]

snipped. . . . .
Also, I don’t know of any data that addresses the effect of chamfer on reliability. Pletcher’s experiments showed it has no effect on speed of ignition.

Pletcher’s data suggest that a pan that was designed to keep the charge close to barrel might increase reliability of ignition, but that’s a bit of a stretch.  He was actually measuring time to ignition, not reliability. . . .

Joe S,
You are correct that I didn't attempt to measure reliability with different vent diameters. In fact I tried for 100% reliability going through cleaning processes that a shooter could not do in any real world shooting session.  I felt that was necessary to collect valid data.
As far as "the effect of chamfer on reliability" having "no effect on speed of ignition" -- I did no testing of chamfer in any of the vent liner tests.  (I did do a test of a straight cylinder vent with a chamfer that showed a slight improvement on speed.  However, the standard deviation was statistically insignificant.  Muzzle Blasts Feb 2000, p.11)

As far as a pan designed to keep priming powder close to the barrel, I wouldn't presume to suggest a pan shape.  I can say with conviction that priming powder close to the barrel (vent) does make for a significant increase in ignition speed. A photography session showed much more fire through the vent when the priming is close to the vent. My gut says that the increased amount of fire through the vent will improve reliability as much as it did speed, but as you say that was not the purpose of my testing. I had 100% ignition reliability because of the cleaning steps necessary for valid data.

Getting back to chamfers, I do have a test in mind that deals with the exterior shape of the vent liner's opening.  It should have been done by now, but time seems to slip away.

Regards,
Pletch 

[bgf]

There is little risk drilling it out to 1/16".  Smaller can sometimes be hard to keep clear under certain conditions, while much larger may self-prime especially with 3f.  1/16" is in the Goldilocks zone .

[Joe S]

My gut says that the increased amount of fire through the vent will improve reliability as much as it did speed, but as you say that was not the purpose of my testing.

I'd agree.  Those photos of yours sure suggest that if things were marginal for some reason, a charge close to the barrel is going to be a whole lot more reliable.  Your photos aren't definitive, but they sure are compelling.