Touch hole gas escape

[Mike in FL]

A rifle builder once told me that a flintlock rifles trajectory was different (worse) than a percussion rifle's, given that everything else was the same - that the flint lock would shoot lower because of the loss of pressure through the touch hole. He was a terrific craftsman and made for me an early Lancaster from a Chambers kit, and a flawless late Lancaster from scratch, both flinters. He has long since moved away but I've always wondered if he was right about the lower velocity. Can't find a thing on Google about that.Looks like I ain't signed in. Mike in FL

 

[Larry (Omaha)]

A rifle builder once told me that a flintlock rifles trajectory was different (worse) than a percussion rifle's, given that everything else was the same - that the flint lock would shoot lower because of the loss of pressure through the touch hole. He was a terrific craftsman and made for me an early Lancaster from a Chambers kit, and a flawless late Lancaster from scratch, both flinters. He has long since moved away but I've always wondered if he was right about the lower velocity. Can't find a thing on Google about that.Looks like I ain't signed in. Mike in FL

I have no data to back up what I say, just some logic: Take two same guns in caliber and barrel length, load the same powder charge in each. The cap lock looses pressure out the nipple, and a flint out the touch hole. Is it equal?? The flintlock will loose more pressure than the cap lock because the nipple and TH are not equal in pressure release size. To compensate, a flintlock may take a tad more powder. Again this is not backed by data, just a little logic.
Larry

 

[Absoroka]

Larry's theory probably has some validity but the difference in muzzle velocity would likely be minor. You have multiple issues that affect the velocity before the ball exits the barrel. Kind of like a Ford/Chevy debate.

 

[flntlokr]

A rifle builder once told me that a flintlock rifles trajectory was different (worse) than a percussion rifle's, given that everything else was the same - that the flint lock would shoot lower because of the loss of pressure through the touch hole. He was a terrific craftsman and made for me an early Lancaster from a Chambers kit, and a flawless late Lancaster from scratch, both flinters. He has long since moved away but I've always wondered if he was right about the lower velocity. Can't find a thing on Google about that.Looks like I ain't signed in. Mike in FL

A good proof of pressure loss is when you attempt to push a stuck ball out by dribbling a bit of powder down the flash hole. How much does the ball move if it was seated to the bottom of the barrel? I have found that I usually have to flash off a couple of little trickle loads to get the ball to move up the barrel enough (if it moves at all) to get about 10 gr. in there; then it MAY shoot out. Usually a percussion gun will shoot it out with about 5 grains put in via the nipple hole. The slow build of pressure is why pyrodex doesn't do well in flinters, I believe.

 

[BillKilgore]

Your builder may have been correct. But it is no big deal to add a little more powder to compensate for pressure loss through the touch hole. The large puff of smoke above the touchhole was the pan flash and the small puff is from the main charge going off in the barrel.

 

[Mgbruch]

Some things just aren't worth fussing about.

 

[ord sgt]

Different version of picture above

 

[TDM]

There is a difference, but as said, it’s a marginal difference. A 1/16” vent hole bypasses more gas than a nipple. Unless the vent hole is too large it’s not a big deal.

 

[Grenadier1758]

While the theory would indicate that there would be more gas escaping through the larger touch hole than the small hole in the percussion nipple and therefore slightly lower chamber pressure, that the flint lock rifle would have a lower ball velocity than the same rifle with a percussion lock. I did some searching through some of the wonderful old "Gun Digest Black Powder Loading Manuals" that had the results of Sam Fadala's testing of many muzzle loading rifles. Surely there would be several instances of the same model with chronograph data. I found a lot of the identical data in the First Edition and the Third Edition. I also only found one instance of comparable flint lock and percussion lock rifles. The rifles were the Navy Arms Ithaca Hawken in Flintlock and the Navy Arms New Model Ithaca Hawken Rifle in Percussion lock.
Pertinent Data: I am only reporting the differences. If the measurements are the same, the second entry is not included.

Flint Lock Percussion Lock
Caliber 50
Barrel Length 32" Barrel Length 34"
Barrel 1" across the flats.
Rate of Twist: 1 in 66"
Depth of Grooves 0.010" approx.
Projectile: 0.490" 177 grain Speer round ball
Powder: GOI (GOEX in 1995)
Patch: 0.015" Pillow Ticking 0.013" Irish Linen
Lubricant: RIG
Ignition: Flint with FFFFg pan powder CCI #11 percussion Caps
Powder measure: Uncle Mike's 0-120 adjustable
Powder Temperature 85 degrees F 80 degrees F

Load Performance
Flint Percussion
Powder (volume) Muzzle Velocity 100 Yard Velocity Muzzle Velocity 100 Yard Velocity
60 grains FFg 1499 fps 914 fps 1493 fps 911 fps
80 grains FFG 1717 fps 999 fps 1712 fps 1002 fps
100 grains FFG 1916 fps 1083 fps 1912 fps 1082 fps
110 grains FFG (max) 1977 fps 1111 fps 2000 fps 1120 fps

In the manual, the flintlock rifle was slightly faster with muzzle velocity until the maximum charge tested. All in all, for only finding one data point, any results don't have a lot of confidence. The same tables were in the first edition.

 

[R Ellis]

Your builder may have been correct. But it is no big deal to add a little more powder to compensate for pressure loss through the touch hole. The large puff of smoke above the touchhole was the pan flash and the small puff is from the main charge going off in the barrel.
View attachment 207107

Great Picture

 

[BillKilgore]

Thanks. It is a frame from a movie my wife made of my first black powder shot.

 

[Rifleman1776]

Larry's theory probably has some validity but the difference in muzzle velocity would likely be minor.

Agree, even less than "minor'. More like 'negligible'. Don't fret the small stuff.

 

[Pietro]

IMO, much todo about nothing.......... both my cap & rock lock rifles zero readily.

I can see no difference except the ignition times of my rocklocks are noticably faster than my capgun's

 

[smo]

Fire in the hole!

 

[oldwood]

Boone didn't worry if his balls lost pressure , he was more interested that his scalp was on his head.

 

[Robby]

I only take issue when there is an issue.
Robby