Can very small changes in flash hole dia effect accuracy?

[kutter]

I'm not new entirely new to BP, just revisting after a very long vacation.
I have been shooting a 50cal FL I built a year ago. Nothing special, siler lock, GM bbl, etc.

I did put a liner in it at the time. It's one I already had from years back,,probably Dixie from the early 70's.
It's flash hole dia turned out to be .054. Me not knowing the difference used it like that and it worked OK.
Seemed reliable, etc.

Reading more, I decided to open it up to 1/16" . The reliability remained but accuracy increased. It really tightened up the groups at 50m. Before I would get 3 shots in a group and 2 others out of the group,,flyers so to speak.
I used the same load and shooting technique, same powder, patch material, lube etc.

Such a small increase. Can that contribute to the more consistant accuracy?
At 62 I ain't getting any better at the trigger that's for sure.
My older brother shoots with me and puts me to shame off hand with it at 50m. The flash hole dia is the only thing changed. He asked if I changed the load the accuracy was so much more apparent even to him.

[roundball]

Hard to say but in my opinion, I'd be inclined to think that you're getting slightly faster ignition, out of the muzzle faster, less time for muzzle wander...but don't know of course.

[omark]

what roundball says sounds the most likely to me, but cant be sure, either.          mark

[wattlebuster]

I will lean in roundballs direction on this one. Faster ignition, better shooting sound reasonable to me

[hanshi]

Agreed.  1/16" is about ideal and should give great ignition.  Can't see how that alone would affect accuracy.

[LynnC]

Like the others I'd say your getting faster ignition while still on target.......Lynn

[kutter]

Thanks for the replys.
That would make sense I guess. Faster ignition,,Less time to change sight picture.
Tell you the truth I couldn't tell any difference in how fast it fired, but asking me to tell the difference in fractions of a second is useless.
I'm sure some of you well seasoned F/L shooters could tell the difference right off.

I'll just chaulk it up to the ellimination of another small variable.
I knew my shooter skills hadn't taken any great leaps recently.

Regards..

[roundball]

I'll just chaulk it up to the ellimination of another small variable.

And the statement you just made I believe is a very important one.

The collective effect of many small variables does indeed affect accuracy, none of which by themselves may be discernible by all individuals.

Just like having sharp flints for every shot, another one I'm a strong believer in is fast 4F priming powder.
Whether or not each individual can detect the difference, by every definition of different granulation size and burn rates, there is no question that 4F is faster than 3F is faster than 2F, etc.

If we made a list of all the variables that affect ignition speed (and there is a direct correlation to accuracy) then tweaked each and every one for max performance, there would have to be a resultant performance improvement, accuracy improvement.

[Dphariss]

I'm not new entirely new to BP, just revisting after a very long vacation.
I have been shooting a 50cal FL I built a year ago. Nothing special, siler lock, GM bbl, etc.

I did put a liner in it at the time. It's one I already had from years back,,probably Dixie from the early 70's.
It's flash hole dia turned out to be .054. Me not knowing the difference used it like that and it worked OK.
Seemed reliable, etc.

Reading more, I decided to open it up to 1/16" . The reliability remained but accuracy increased. It really tightened up the groups at 50m. Before I would get 3 shots in a group and 2 others out of the group,,flyers so to speak.
I used the same load and shooting technique, same powder, patch material, lube etc.

Such a small increase. Can that contribute to the more consistant accuracy?
At 62 I ain't getting any better at the trigger that's for sure.
My older brother shoots with me and puts me to shame off hand with it at 50m. The flash hole dia is the only thing changed. He asked if I changed the load the accuracy was so much more apparent even to him.

Who can say?
I would not think that .006 difference in diameter would change anything. But one really never knows what can occur.
Could be the slightly larger vent with its slightly increased gas flow makes for a pressure curve the barrel likes?
I would test it again.

Dan

[Daryl]

You might not be getting better, but you are becoming more practised with that gun and that will improve accuracy and help to eliminate said 'fliers'.  Just like you said, small changes add up. Practise is good.

[LynnC]

Check my math, I calculate a 30 percent + increase in the area of the vent opening just going from .054 to .0625.  That ought to signifigantly speed ignition.  1/16 is the smallest vent on any of my flint guns.  I like to open the vent a little ata time untill I get fast consistant ignition.  Your milage may vary

[B.Habermehl]

.062-.070 appear to be about the ideal range of diameters for touch hole. Much bigger and you often will see accuracy drop off. One chunk gun shooter I know just changed his out when it reached .070, from .062 and claimed better groups. I would think that these guys are about as fussy as the bench rest boys about controling variables. A off hand or hunting shooter will never see a difference untill it wears a good bit more. My hunting guns have .070 touch holes and they shoot way better than I can shoot them off hand.

[Daryl]

Not sure about not seeing it if shooting offhand. Double the group size from 1" to 2" and it adds to the & at 50 yards it adds at least another 2" to the tightest possible group you can shoot. I notice on a lot of gongs, there are a lot of shots around the perifery, that if the gun added an inch to the group, it would have missed.  On paper, with rings only 1" in diameter, you've the potential for taking off points every shot.

The reason I used doubling the size by going from .062" to a .070" vent, I think was a test done by the Bevel Bros (or someone else some time ago.

[B.Habermehl]

Perhaps you are a better off hand shooter than me.     Having fooled around with touch hole dias. in my own guns, I have only found my best accuracy corresponds with quickest ignition. I have used .070 in my big bores >.54 and .062 in smaller bores. Just my own unscientific observation.

[Daryl]

I was comparing my .40 and .45 with .054" and .070" holes. The .54" vent is more accurate, that seemed obvious - and, perhaps you are right - maybe not.  I wouldn't worry about a .54 cal. rifle's vent hole being .070" either.  If you can handle the recoil (as little as there actually is), a .54 is has greater accuracy potential than the smaller bores - as does any bore size larger than .54".  Such things as vent hole size have less and less effect, the larger the bore.

[George Sutton]

Changes in vent hole size will absolutely effect accuracy.

Centershot

[Candle Snuffer]

I agree with Centershot.

A larger vent hole means more volume of gasses escaping through the vent, thereby taking away from gasses pushing the ball.

Smaller vent hole should work just the opposite.

[Daryl]

The larger flash holes have a negetive effect on the shot to shot consistancy of the load, which in itself reduces accuracy.  Of course, this can be measured - and has been.  How much it effects larger bore sizes in comparrison, is not known by me, but as with anything involving shooting, the smaller the bore, the more critical the consistancy of everything involved, becomes.

[Standing Bear]

In my experience, changes in flash hole size only affect vertical point of impact.  Group size remains approximately the same.  This with a .40 cal hunting/100 yard load of .395 ball and 75 gr FFg.  Touch hole opened up past 5/64 and 100 yard POI dropped about 3" but change was slow and not instantaneous.  A new liner opened to 1/16 and she was right back on target.
TC

[Larry Pletcher]

I agree with others here that the vent size can affect accuracy.  I would also suggest that in timing I have done, how clean the vent is can be a bigger variable.  After a timing session I pushed a drill bit through a vent and pushed out a neat little tube of fouling that had lined the vent.  This tube of fouling would have decreased the vent size significantly.

Pic #1 - the bit is pushing the fouling tube out of the vent.


Pic #2 - here is the fouling tube free from the vent.


Pic #3 - looking through the fouling tube.


I didn't try to measure the reduction in diameter caused by the fouling, but suggest that fouliong has a bearing on vent diameter.

Regards,
Pletch

[C Wallingford]

Larry--
Was the rifle discharged when this fouling built up or was this one of your tests with just a flash in the pan?
I am thinking that the pressure from the discharge would have blown that out of the touch hole.

[Larry Pletcher]

Larry--
Was the rifle discharged when this fouling built up or was this one of your tests with just a flash in the pan?
I am thinking that the pressure from the discharge would have blown that out of the touch hole.

Hi Charlie,
You're right in thinking it wasn't a full power load.  The barrel was a stub with a sabot in front of the charge.  I don't remember the load, but it obviously wasn't a normal rifle load. My gut says we would have used 15 grains or so.  I don't know how much of this would be retained in a normal rifle shot.

Thinking about your comment, I wonder if there is a way to measure  how much stays in the vent with a full power load.  It would take a barrel with a removable vent, fired multiple times, and then remove and examine the vent.  Currently all my rifles have permenently installed vents or Snyder-internal cone.  Since I don't want to mess with those guns, I'll just suggest that the fouling in full power loads will be somewhere between "clean" and the fouling tube in the photo.  I'd guess , but what kind of science would that be.  "I don't know" is honest.

Merry Christmas,
Larry

[Daryl]

Larry--
Was the rifle discharged when this fouling built up or was this one of your tests with just a flash in the pan?
I am thinking that the pressure from the discharge would have blown that out of the touch hole.

Hi Charlie,
You're right in thinking it wasn't a full power load.  The barrel was a stub with a sabot in front of the charge.  I don't remember the load, but it obviously wasn't a normal rifle load. My gut says we would have used 15 grains or so.  I don't know how much of this would be retained in a normal rifle shot.

Thinking about your comment, I wonder if there is a way to measure  how much stays in the vent with a full power load.  It would take a barrel with a removable vent, fired multiple times, and then remove and examine the vent.  Currently all my rifles have permenently installed vents or Snyder-internal cone.  Since I don't want to mess with those guns, I'll just suggest that the fouling in full power loads will be somewhere between "clean" and the fouling tube in the photo.  I'd guess , but what kind of science would that be.  "I don't know" is honest.

Merry Christmas,
Larry

Larry's logic above as well as actually looking at the vent after it's loaded, shows his statement to be more than logic with the charges I use.  The vent shows no buildup and barely discoloured steel in the cent, with the powder charge sitting right at the hole - very little 'bridge' is seen as the vent hole has barely any 'depth' to it - barely "a thin wafer sir"? (of steel separating the internal charge from the pan)

[George Sutton]

I guess Larry's finding are a good argument for picking the vent prior to each shot.

Centershot

[Daryl]

I looked into my vent, each and every shot today - mind you it was a short day, no more than 35 shots. The vent remained clean, shot to shot without any buildup.  I was shooting my .40 - .064" vent using a .398" pure lead ball in the .398" bore, .022" to .025" patch depending on which took is used to measure them pushed by 75gr. 3F GOEX.