Vent hole liner

[Gvilleddie]

I’ve been shooting a flintlock with a vent hole that measures 3/32”. Is this too large? When I load, some of my ff powder is pushed into the pan. If I need a liner, do any of you Alabama boys know of anyone in north Alabama who can do this job? Thx, Gville

 

[Spikebuck]

If your gun shoots accurately and fires off every time, then I guess it's not too large. On my rifle with a direct drilled hole it is 5/64" with a slight cone on the surface, so I'm not too much different...just a tad smaller opening. I don't get any of my 2F coming out. Very good ignition, though I "think" it's a tad slower than my other rifles with liners. The gun is very accurate with that setup. I think the concern I hear most often about touch holes being "too big" is that it allows pressure to escape there and may cause inaccuracy if those pressures vary.

Now this next part is my opinion because I'm kinda picky....I know others worry less than I do....but I would be careful about installing a liner if your current touch hole is coming through right in front of the breech plug face (mine does). Putting a touch hole liner in may break the plug seal exposing threads which will let corrosives from the burned powder and moisture from cleaning enter the plug threads. Some report that this is not an issue, but my personal choice is to not compromise that seal. To each his own.

 

[Vaino]

All my later builds have a White Lightning TH liner and I drill the existing hole w/ a 1/16 drill. I use the 1/4 dia liner and locate the center 5/32" from the plug face. Have experienced no problems w/ the WL......Fred

 

[hanshi]

I prefer the vent hole to be as small as possible while delivering absolutely reliable ignition. Larger than that is wasting energy that would otherwise go toward giving the prb a bit harder kick.

 

[rafterob]

If you are not getting excessive blowback out of the pan there is no worry. You will know when that happens, sh*t will be flying in your face.

 

[Col. Batguano]

The name of the game is total barrel dwell time. The the total time it takes from sear trip to have the ball exit the muzzle. The shorter (elapsed time) the better. The TH is a component of a whole series of components involved in the process.

What you're after with the flint / frizzen / pan / TH / main charge chain is the fastest total barrel dwell time that is absolutely reliable. So changes in any of the components are going to affect the total barrel dwell time. Most people have settled on 1/16" as a good middle ground number for TH size, but I've heard of TH sizes as small as .055", and as large as .100". Generally, the larger the caliber and powder grain size (in your main charge) the larger the TH size is used. I personally use a TH size of .060" because I don't totally clean between shots (fouling in the TH impeded the pan fire from getting through there), and usually ue 3Fg as my main charge powder.

TH size is a balancing act. The larger it is, the easier (and probably faster) the pan fire will be to ignite the main charge. On the other hand, the ball won't start moving forward until the pressure builds to a large enough extent to ignite it. A larger hole will allow more gas to escape through it, and more powder will have to burn before the pressure on the ball builds to the advancing stage. An (inside) coned vent liner is a mechanism to allow the fire coming from the outside to come in contact with as much main charge powder as possible once it gets through the opening, but limiting the opening size.

Once the main charge is burning, any escape of gas through the igniting hole (or gas blow by around the ball) is going to slow the pressure build in the chamber. / under the ball. That's why cartridge guns and cap locks have so much shorter barrel dwell time than guns with touch holes.