Vent hole size

[brushblind]

What is a good size for a 12ga fowler vent hole? It now has a drilled 1/16th vent but isn't very consistent, picking the vent doesn't help much but I always do. Filling the pan full gives ignition but with the slow fuse effect. Thinking about maybe stepping up a size on the vent, what say ye?

 

[TDM]

What type of vent are you using, is it hollow based?

 

[Grenadier1758]

The good size, @mmull56, is the size of the touch hole that gives reliable ignition. To best help you out, we need to know the configuration of your breech. So, tell us about your fowling gun. Who is the manufacturer? Is the gun new or used? What style of breech do you have? Is it a traditional breech or a chambered breech? Where is the touch hole with respect to the face of the breech? How often have you shot your fowling gun? Have you flushed out the breech with something to cut any old oils or built-up fouling? I use a heavy rinse of rubbing alcohol. I also use a welding tip brush from Harbor Freight to aggressively remove gunk from the touch hole. If there is a chambered breech, that chamber needs some cleaning just as a general practice. @TDM's question of the vent liner is useful. Do you have a vent liner or a simply drilled touch hole? Does the liner (if you have one) protrude into the bore? That can capture fouling and bridge into the touch hole. Are you getting reliable pan flashing?

 

[DuncNZ]

I use White Lightning flash hole liners on all my Flintlocks , I drill the flash hole to 3/16th" and very lightly chamfer the outside edge with a ¼" finger turned drill bit .I prick the flash hole after loading , I use 3 gr of ffffg powder heaped to the just under the flash hole and get excellent ignition , it suits me .

 

[nhmoose]

Like self-priming barrel?

 

[deerstalkert]

Mull, one trick i have found that a SMR i built likes is for me to leave the vent pick inserted when i powder and seat the ball. fires every time if this is done. if i pick to clear the vent, then charge, then pick again i will have about 20% flash in the pan.
something about the pick leaving a flash channel through the charge i guess.
something you may try.
my flintlocks all have 1/4x28 vent liners with 1/6 vent. i trim the liners flush with the inside of the barrel, cone and polish.
i place the vent hole 5/32 ahead of the breech plug if it is just a flat faced plug. and that's all i use so thats how i do all of them. the liner threads just clear the breech face by a whisper. if i do it right

 

[ohio ramrod]

Several years back there was an article in muzzle blasts ( bevel brothers )that determined 1/16 was the best size vent hole for consistant ignition and accuracy. If you are having problems I don't think the vent hole size is the problem. My flints all have 1/16 drilled vents and work fine if the flint sparks.

 

[SDSmlf]

I drill the flash hole to 3/16th" and very lightly chamfer the outside edge with a ¼" finger turned drill bit .

Are you sure about your recommended touchhole size? 3/16” or .188” diameter is a much larger than usual touchhole.

 

[user 48702]

Are you sure about your recommended touchhole size? 3/16” or .188” diameter is a much larger than usual touchhole.

Agreed, 3/16" (.188) diameter is larger than the touch hole on a field cannon which was about .175 diameter.

 

[Eric Krewson]

I have a white lightning liner in my 12ga, I opened the touch hole to 5/64 to get a little better ignition, I liked this well enough to drill all my larger bore touch holes out to 5/64 as well. I use a 1/16" hole on my .40s.

3/16" has to be a typo, way too big.

 

[brushblind]

As far as I can tell the breech plug has a shallow divet in the middle but the vent is drilled just in front of the plug face. Inserting a tooth pick goes all the way across the front of the plug and touches the inside of the barrel on the opposing side. It may be what I'm seeing on the face of the plug is just from the light playing on it, but it's not a "chambered Breech setup. No touch hole liner, has a 1/16th drilled hole just in front of the breech face.

 

[brushblind]

Mull, one trick i have found that a SMR i built likes is for me to leave the vent pick inserted when i powder and seat the ball. fires every time if this is done. if i pick to clear the vent, then charge, then pick again i will have about 20% flash in the pan.
something about the pick leaving a flash channel through the charge i guess.
something you may try.
my flintlocks all have 1/4x28 vent liners with 1/6 vent. i trim the liners flush with the inside of the barrel, cone and polish.
i place the vent hole 5/32 ahead of the breech plug if it is just a flat faced plug. and that's all i use so thats how i do all of them. the liner threads just clear the breech face by a whisper. if i do it right

I'll try that!

 

[brushblind]

The good size, @mmull56, is the size of the touch hole that gives reliable ignition. To best help you out, we need to know the configuration of your breech. So, tell us about your fowling gun. Who is the manufacturer? Is the gun new or used? What style of breech do you have? Is it a traditional breech or a chambered breech? Where is the touch hole with respect to the face of the breech? How often have you shot your fowling gun? Have you flushed out the breech with something to cut any old oils or built-up fouling? I use a heavy rinse of rubbing alcohol. I also use a welding tip brush from Harbor Freight to aggressively remove gunk from the touch hole. If there is a chambered breech, that chamber needs some cleaning just as a general practice. @TDM's question of the vent liner is useful. Do you have a vent liner or a simply drilled touch hole? Does the liner (if you have one) protrude into the bore? That can capture fouling and bridge into the touch hole. Are you getting reliable pan flashing?

It's a contemporary built from the 1970's, has a LOTT lock, seems to be a very well built trade gun/fowler, no vent liner.

 

[deerstalkert]

As far as I can tell the breech plug has a shallow divet in the middle but the vent is drilled just in front of the plug face. Inserting a tooth pick goes all the way across the front of the plug and touches the inside of the barrel on the opposing side. It may be what I'm seeing on the face of the plug is just from the light playing on it, but it's not a "chambered Breech setup. No touch hole liner, has a 1/16th drilled hole just in front of the breech face.

exactly the setup i use in my builds.
try the vent pick inserted in the vent while charging and see if it helps. works every time for me. thinking about it (difficult before the second cuppa) i think the probe leaves a flash channel the entire width of the powder charge. also this method is a secondary way of determining that the patched ball is compressing the powder with no air gap. first tell being the groove i carve in the rod at the muzzle.

 

[Rock Home Isle]

3/16” has to be a typo…at that size, the pan would be self-priming.

 

[Ed Pilkington]

.50 CVA converted from percussion rifled to flint19 gauge smoothbore. i cut the bolster off, then drilled, tapped and chamfered 1/4 vent liner and installed same year and make CVA lock. Sporadic firing. Read here that 1/16 was good opening for vent hole. I enlarged it, bought best flints i could find…she hasn’t misfired one time since. I promptly became a supporting member of MLF.

 

[BadDaditood]

3/16” has to be a typo…at that size, the pan would be self-priming.

Yes! Unless frizzen is open, in which case barrel would be self emptying!

 

[Grenadier1758]

It's a contemporary built from the 1970's, has a LOTT lock, seems to be a very well built trade gun/fowler, no vent liner.

Your fowling gun sounds very much like a fowling gun I have. It too is a gun built about 1970 from a collection of parts that were available to the builder. Club members have referred to it as a West (St. Louis) County Special. Others would refer to it as a Franken Fowler. It has the Lott lock as that was just about the only lock suitably sized for a trade gun. The earliest guns from North Star West used Lott locks. Generally, not considered the best of locks, but they can be made to work reliably. Of course, the 1850's brass scroll trigger guard was just too out of place. The barrel is a full choked 12 gauge. I am tolerating the 1795 dished out comb in the stock. The vent hole is perhaps a bit larger than 1/16" and reliable.

Now one of the first things I would do before drilling out the touch hole would be to lightly chamfer touch hole entry for smoother flow of the flash from the pan getting to the powder chamber. The suggestions of using a brush or vent pick to keep the flash hole clean are good. I do that with a set of Harbor Freight paint gun nozzle brushes. The last step is to open the touch hole to 5/64" or one of the number bits that are between.

 

[hanshi]

Every flint gun I have has the vent hold 1/16" as the default size. I remove the liner from the new gun and open the inside cone even more; I don't cone the outside. So far I've had great ignition with all of them at 1/16". I insert a feather, pick, etc, in the vent hole when I load the main charge. The amount of prime in the pan, under normal conditions, is about 3 grains of 4F or 3F. All the liners are ss and are very resistant to burnout. I do have one rifle that the vent hole may have enlarged just an infinitesable amount, or maybe I just wiggled the drill bit a little in the first place. My flint smoothbore is 1/16" and is dead reliable.

 

[Rock Home Isle]

Every flint gun I have has the vent hold 1/16" as the default size. I remove the liner from the new gun and open the inside cone even more; I don't cone the outside. So far I've had great ignition with all of them at 1/16". I insert a feather, pick, etc, in the vent hole when I load the main charge. The amount of prime in the pan, under normal conditions, is about 3 grains of 4F or 3F. All the liners are ss and are very resistant to burnout. I do have one rifle that the vent hole may have enlarged just an infinitesable amount, or maybe I just wiggled the drill bit a little in the first place. My flint smoothbore is 1/16" and is dead reliable.

This right here