vent hole size

[Ken G]

I've heard repeatedly that a large vent hole would have a neg. effect on accuracy.  I'm going to show my lack of knowledge.  Why? 
I understand fully that with a bigger hole you lose pressure but it's the same size hole with each shot so you should lose the same amount of pressure each shot?  Right?  What am I missing?
How much acccuracy difference between say a 1/16" vent hole and a 5/64? 
Thanks in advance. 
Ken

[Larry Pletcher]

I've heard repeatedly that a large vent hole would have a neg. effect on accuracy.  I'm going to show my lack of knowledge.  Why? 
I understand fully that with a bigger hole you lose pressure but it's the same size hole with each shot so you should lose the same amount of pressure each shot?  Right?  What am I missing?
How much acccuracy difference between say a 1/16" vent hole and a 5/64? 
Thanks in advance. 
Ken

I confess that I'd like answers on this too.  All I have numbers on deal with consistency of ignition times and not on accuracy.  Blown nipples on LR bullet guns effect accuracy, but I don't know if there is connection that concerns flint vents.  I look forward to any thoughts especially "why" -- and can it be tested.

Regards,
Pletch

[Candle Snuffer]

I would think that the accuracy lose would come from an inside coned vent liner once it became fouled and started to restrict the gasses escaping from the vent hole. 

Most likely the best way to prevent any lose of accuracy would be to place a feather quil in the vent on loading each time, thereby assuring no change in the vent hole restrictions (if the rifle has an inside coned vent liner).  I would expect a few warm up shots would be needed to establish the equalness of the hole with the feather quil.

Just my thoughts.

[Daryl]

If nippely guns lose accuracy with blown nipples, why wouldn't flinters lose accuracy with oversize vents? Pure conjecture.

I'm not sure a flinter would lose accuracy- it certainly would with the load developed with a small vent- due to loss of velocity in the load and therefore less accuracy. If loaded to ensure the same velocity as before, wouldn't the accuracy be the same.  Here's some more guesswork - if the accuracy load was 60gr. 3F, with a 1/16" vent, a 'blown' vent of .80" would probably require 75gr. or more just to match previous accuracy.

[northmn]

An individual gave me a 45 to replace a vent for.  Seemed he tried a light load of powder and the charge vented through the touch hole.  It is possible at some point the pressure consistency goes.  A .07 vent like some recommend will self prime to some extent with 3f, meaning a powder loss and possible inconsistency.  On a relted issue, I have also wondered if vent size cannot be to some extent realted to bore diameter.  Some of the old muskets were about 3/32, but also over 12 bore.  Daryl's suggestion about a powder increase makes sense.  Just throwing out thoughts as I don't know either.

DP

[Larry Pletcher]

I see some chances at more testing here.  I have a different interface coming in the mail this week that may give us a chance to find more answers here.
With what I use now I can't test outside because ambient light triggers the photocells.  The new setup appears to give me control over the level of light necessary to trigger the cells.  Testing outside means I can use photo cells at pan and muzzle of a real gun using full powder loads while chronographing at the same time.

Consider a test where we start with target or hunting load with a WL liner with a 1/16" hole.  We measure ET from pan to muzzle and chronograph the load.  Do a 5 shot average on both. Then we drill out the hole to .064 and repeat.  Perhaps do a .067, .070, etc.

We can then compare the ETs and velocity or (velocity loss) as the vent increases in size.  I could see a loss in velocity being related to the increase in the area of the vent.  I could also see a increase in the "Barrel ET" and the liner diameter increases.

We have plenty to finish right now, but this might be a worthwhile test for warm weather.  I haven't checked with my partner in crime, but I bet a can get help.

Regards,
Pletch

[William Worth]

Just a thought here Larry, would you have the means to measure pressures, aside from velocity changes.  I have always been led to believe that at lower pressures, powder ignition and burn rates become more erratic.

[roundball]

All the Flintlocks I have use vent liners that are heavily coned inside and out, with .070" vent holes... .40/.45/.50/.54/.58/.62cals.

Three in particular (.45/.50/.54cals) each have a few thousand shots on them and I haven't seen any change in accuracy so far...

[Larry Pletcher]

Just a thought here Larry, would you have the means to measure pressures, aside from velocity changes.  I have always been led to believe that at lower pressures, powder ignition and burn rates become more erratic.

At this point I can't measure pressure.  In the example I gave above,  The best I can do is chart velocity and Et in the barrel decrease as the vent is opened.  What I expect will happen is that the drop in velocity will relate to the increase in area of the vent rather than the increase in diameter of the vent.  I would also speculate that the hotter the load the more pronounced the effect.  None of this may result in a change in accuracy.  Instead it may require the need to work up a new accuracy load.

Regards,
Pletch

[tg]

I don't think there will be any loss of accuracy as long as you can load the gun the same every time, I punched out a couple of the vents on rifles(they are all gone now as I only shoot smoothies) to 5/64 and did not see any noticable accuracy difference, I also went to 5/64 with my Virginia smoothrifle and it is as accurate as before, I used a 5/64 vent on the last gun I did (French Fusil) and it shoots fine, these guns always go off if you can drop at last a little chunk of hot steel into the pan. That is my experience,( all the guns I opened up were .50 and above.)FWIW

[Daryl]

Don't think I'd let a vent go to 5/64's if I could help it - that's .078" and would almost self-prime with 2F.

 I know you could buy new guns in England with self-priming locks, and expect they were similar - merely larger vent holes.

 I think Larry's on the right track - with vent area increases instead of merely picking sizes.  A graduated scale of velocity versus area will be interesting for sure.

I recall from a previous forum I was on, one of the fellows noted a loss in velocity from his original vent size of around .070" (might have been .064") to the burnout size of .80" as a loss of 200fps in his .54.  Of course, one fly 'speck' in this ointment is possibly of changing powder lots between chronographing.

[Roger Fisher]

Just a thought here Larry, would you have the means to measure pressures, aside from velocity changes.  I have always been led to believe that at lower pressures, powder ignition and burn rates become more erratic.

At this point I can't measure pressure.  In the example I gave above,  The best I can do is chart velocity and Et in the barrel decrease as the vent is opened.  What I expect will happen is that the drop in velocity will relate to the increase in area of the vent rather than the increase in diameter of the vent.  I would also speculate that the hotter the load the more pronounced the effect.  None of this may result in a change in accuracy.  Instead it may require the need to work up a new accuracy load.

Regards,
Pletch

Only speculating (I can't recall ever being called scientific minded!  Since as the vent hole is at and starts to exceed that 5/64th limit the process of loading i.e. pushing the patched ball down onto the unpacked powder self primes her and the question that would bolix up a test is how much 2 f powder is lost each time and would certainly vary in amount.  I refer here to Goex, since that is a dirty powder compared to the Swiss...

[Leatherbelly]

 Roger,
   Is Swiss powder cleaner burning than others? I've never seen it in Canada so it makes a mind wonder. Gosh,I shot 40-50 shots today with 2f Goex and  clean-up was a breeze. Five patches and done. I'm using 50 grs. of 2f goex in my forty.
  Shot a nice trail today also.Not many misses,(2 or 3) great light with slight overcast.60% R/H. All six of us shot well.

[tg]

"--------------------------------------------------------------------------------

Don't think I'd let a vent go to 5/64's if I could help it - that's .078" and would almost self-prime with 2F.'

I didn't let it go, I drilled it to 5/64, I shoot 3f and it is quite accurate and consistant, more than enough for any shot loads and deer huting at the close smoothbore ranges, it might not work in the world of using every little trick to squeeze the most out of a ML but I have chosen the path that offers the closest thing to the experience that those who used the oriinals would have had and I have been quite happy with this methodology and the lack of Chrongraphs/high speed photos, weighing powder charges and balls and all the tech/tweeking many use to upgrade the perfromance of the ML, this is fine for those who are into such but I like to keep it simple and in the 18th century mindset.

[northmn]

When I did some chronographing I opened my 54 to .070 from .0625.  I believe I noticed about a 50 fps reduction in velocity, whcih I passed off to other variables.  The .070 does tend to self prime with 3f and a 5/16 would also.  That is not a real problem as one can stick a vent pick in the vent when loading which I like to do anyway.  My repro Brown Bess had a 3/32 hole or about that and was very realiable even when primed with 2f.  I think it might have a little to do with bore diameter as a 40 or less may vent out more with a larger hole.  A matter of proportion to bore size.  May affect accuracy in that manner also.  But it would require a certain amount of testing to know.  ?

DP

[Larry Pletcher]

didn't let it go, I drilled it to 5/64, I shoot 3f and it is quite accurate and consistant, more than enough for any shot loads and deer huting at the close smoothbore ranges, it might not work in the world of using every little trick to squeeze the most out of a ML but I have chosen the path that offers the closest thing to the experience that those who used the oriinals would have had and I have been quite happy with this methodology and the lack of Chrongraphs/high speed photos, weighing powder charges and balls and all the tech/tweeking many use to upgrade the perfromance of the ML, this is fine for those who are into such but I like to keep it simple and in the 18th century mindset.

I have no problem with your shooting philosophy.  I use the same ideas in real world shooting too.  I prime, slap the lock to level the prime, close the frizzen and shoot.   I believe that the fellows who have helped me also have the same philosophy as you when hunting or target shooting. 

All the steps I'm going through here are basically to learn what makes a lock fast or what makes one vent faster than another in a lab setting - if you can call my garage a lab.    Driven by these ideas I have to eliminate variables when ever I can.  As an example, I weighed the priming powder not cause I do in the field, but because I don't want varying amounts to be the reason for a change in the timing results. 

Will any of this make me a great shot?  No! But I get a hoot out of learning and enjoy the challenge of finding out what makes a flintlock tick.   Put us in the woods together and we're on the same page.

Regards,
Pletch

[Acer Saccharum]

Speaking from the vast storehouse of fact and dustballs* rattling around my noggin:

From the long range percussion shooters, the nipple is key to accuracy, a platinum lined, precise orifice. Once the orifice starts to open up, the accuracy drops off. I assume this is because the pressure drop becomes erratic as the orifice opens up.

I don't know if any of the above relates to flint. I assume there would be some crossover, but never read about it, nor tested for it.

Acer

*dustballs: made up information that sounds plausible, but in fact, is conjecture.

[Roger Fisher]

Roger,
   Is Swiss powder cleaner burning than others? I've never seen it in Canada so it makes a mind wonder. Gosh,I shot 40-50 shots today with 2f Goex and  clean-up was a breeze. Five patches and done. I'm using 50 grs. of 2f goex in my forty.
  Shot a nice trail today also.Not many misses,(2 or 3) great light with slight overcast.60% R/H. All six of us shot well.

I'm told that it is since I use the Goex.  If I would go to Swiss I would have to experiment more with my offhand shooter and I have 'othrs' to work on.  Since the Swiss is hotter (and costly) we cut the charge from Goex to Swiss by abt 15%.  Its that 'about' that makes me hesitate to use it altho I have 'some'.  I do know that looking at it in the palm of the hand along side of a small amt of Goex it is clear that the goex is dirty and has more slabs and splinters.  Swiss is even in size and shiny.  Good to hear that you folks can get out of the cabin and shoot...and well too!!

[Daryl]

  A matter of proportion to bore size.  May affect accuracy in that manner also.  But it would require a certain amount of testing to know.  ?
DP

I'd considered the proportion deal in relationship to the big increase in pressure that the small bores provide - using normal target loads.  The greater the pressure inside the barrel, the greater the pressure coming out the vent therefore - larger bores will 'admit' to a larger vent size than will a smaller bore.  The smaller the bore, the smaller the vent should be.

Another way of looking at it - with a .100" vent, a Bess will still project the ball with a piddling 70gr. charge.  A ratio charge in a .36 cal would be about 7 to 10 grs. How fast do you think a .36 will project a ball, if the vent was .100" in diameter, using that 7 to 10 gr. charge? With a tight combinaton, it might not move more than marginally forward, while the 'charge' spewed out the vent.

[Dphariss]

Larger vents tend to produce larger velocity deviations and I have always heard less accuracy.
Properly done I see no reason for a vent larger than .060-.065and by the time I had a chrono I was past using 3/32 vents. As a result I never checked this. I would not waste my time makeing a 3/32 size vent in a rifle since I would just have to change it back after testing anyway.
Large vent is a waste of powder is several ways, pressure loss, powder blown out the vent etc.
Its like throwing away 10-20 grains of powder every shot.
Dan

[tg]

Pletch, I have enjoyed your tests and they areimformative and interesting, at times though I see a trend toward milking every bit out of a ML that suggests the habits of those who handload, develope wildcat loads for centerfires, I find ML shooting more rewarding if I develope my load with out a lot of tech support and just keep it simple, a 1 1/2" group at a given distance is as good as an inch for most ML usage, I guess there are a lot of things that I don't need to know as long as I can get what I need out of my gun for hunting and trail walks, the few grains of powder wasted or the lack of consistancy by a few FPS and such things are not important. I would just rather shoot my gun based on what it has taken to find a good load the old ways, more power to those who choose to make things more complicated, I am certain it is all very interesting to you, my stick just floats ina different direction.

[northmn]

For a hunting rifle I lean towards TG's philosophy in that reliability is more important than the ability to hit field mice at 100 yards if the gun goes off.  When I used to shoot 32's I got good accuracy with a 1/16" vent.  Going back to the discussion concerning the relativity of bore size to vent size I wonder if it makes a lot of difference other than pressure release, which as Dan points out is like losing 10-15 grains of powder.  I used to know an individual that always thought that vents were put in backwards, that the larger hole should be to the outside to funnel the priming into the barrel. He was a good shot.  My copies of English rainproof locks tend to support that theory as they have a channel system built in.  While Larry's experiments tend to show that that would slow ignition, it may be more reliable.  I countersink and make a funnel from the outside instead of opening up the hole a great deal.  While it has worked for me, I will make  no outstanding claims for the system either.

DP

[roundball]

While the hex wrench design vent liners are definitely not "HC"...that large hex well provides that external funnel effect...extremely fast ignition

[Larry Pletcher]

snipped. . . . .  I used to know an individual that always thought that vents were put in backwards, that the larger hole should be to the outside to funnel the priming into the barrel. He was a good shot.  My copies of English rainproof locks tend to support that theory as they have a channel system built in.  While Larry's experiments tend to show that that would slow ignition, it may be more reliable.  I countersink and make a funnel from the outside instead of opening up the hole a great deal.  While it has worked for me, I will make  no outstanding claims for the system either.

DP

In a test I ran on straight cylinder shaped vents in 2000, I tried an exterior cone on 1/16" vent hole.  The exterior cone dropped the time from .044 seconds to .0406 seconds.  This made me add an exterior cone to my personal rifle.  The test obviously wasn't done on enough different vent sizes to make a major pronouncement, but is worth noting.  It should be said that when dealing with liners, installing an exterior cone must be done with care as you could go too deep and go through the web.

Regards,
Pletch

[Daryl]

With the White Lightening Liners, the deeper you seat the liner's bevel, the thicker will be the 'wall' between the inner cone and the outside.  The 'bevel' cutaround the threads should be deep enough to seat the liner to it's full depth.  Seating it too shallow will result in replacing it early. My first one burnt out fairly quickly, as the bevel cut in the barrel was very shallow, resulting in a very thin wall.