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Old February 3, 2021, 04:13 PM   #1
Cannonfuse
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Touch hole, barrel length and pressure loss.

I read that the pressure escaping from the touch hole in a muzzleloading rifle can be compensated with a slightly heavier powder charge.

Is this true when it come to muzzleloading pistols with short barrels too? In modern pistols and revolvers, fast burning smokeless powder is used to increase the pressure fast to compensate for the short barrel length. Black powder (and equivalents) generates lower pressure than modern pistol powder, and with a touch hole even more pressure will escape.

So my questions are, how does the length of the barrel and the size of the touch hole affect the pressure in the barrel? If my barrel is 3.5” long and the touch hole is 0.06”, and I use a powder charge of 40 grains of pyrodex (with a 120 grains roundball), how much should I increase the charge to compensate the loss of pressure? (For example, will 45 grains with touch hole perform equivalent to 40 grains without touch hole in a 3.5 inch long barrel?)
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Old February 4, 2021, 10:12 AM   #2
Oliver Sudden
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Touch hole imply s a flint lock and they are not suited to Pyrodex.
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Old February 4, 2021, 07:19 PM   #3
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It seems to me that you may want to go the other direction... less powder.

With a 3 1/2 inch barrel there is going to be a lot of unburned powder.

Work up to that sweet spot where you get peak velocity and accuracy without excess powder being wasted.
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Old February 5, 2021, 08:39 AM   #4
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I agree with maybe trying less. You are only going to burn so much in that short barrel.
Also, you may be overthinking this. The firearms in question... BP pistols....have been used for centuries. I kinda doubt that compensating for pressure loss at the touch hole/flash hole/
Nipple hole was high on the list of things to do to improve performance.
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Old February 5, 2021, 12:27 PM   #5
Aguila Blanca
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What kind of pistol do you have that has a touch hole? I don't consider the nipple of a cap-and-ball pistol to be a "touch hole." It's covered by a cap, and as the round is fired the hammer holds the cap in place. How much pressure do you think is going to be lost? And what makes you think that suggested/recommended loads haven't already taken that into account.?

Lastly, what pistol do you have that takes 40 grains of black powder?
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Old February 5, 2021, 06:44 PM   #6
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My black powder pistol experience is EXTREMELY limited but I used to shoot with a friend that had a Ruger Old Army and it was definitly a hoot to deal with the Crisco, the powder and the caps.

If I remember correctly he used 40 grains black powder with a .457 round ball for a "full" charge and 20 grains for a target load.

I don't remember the weight of the round ball just thought it was odd that a .44 revolver took a .457 ball. It usually shaved some lead seating the ball in the cylinder but he claimed that was a good indication he had a "good" seal.

Caps were somewhat hard to come by back then and he said he had problems with foreign made caps and not knowing if a 10 or 11 size cap was going to fit.

NOTE: My friend warned me about the incredible danger of the Ruger Old Army black powder revolver being that if his wife ever caught him in the kitchen in the midst of cleaning the thing he would undoubtedly be a dead man. (Boiling water and an old tooth brush to clean the thing and dry the thing out in the oven on an old cookie sheet etc.)
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Old February 5, 2021, 09:30 PM   #7
Oliver Sudden
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Note he says .06” touch hole. That’s not a nipple but the vent size for a flintlock.
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Old February 5, 2021, 11:23 PM   #8
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Not a black powder expert, but my understanding is a touchole only applies to matchlocks and cannon where the burning fuse is touched to the hole to fire the weapon.

Flintlocks have a "flashole" or "vent hole" and caplocks have nipples the cap goes on.
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Old February 18, 2021, 10:10 AM   #9
bladesmith 1
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Well, if we're gonna get picky about terminology, a matchlocks burning wick ignites the priming pan, not the main charge through the hole in the barrel above the pan. I've shot match locks and flint locks for over 40 years and have always considered the hole in the barrel next to the pan a touch hole. And, I've never worried about pressure loss, just hitting the target. JMHO
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Old February 18, 2021, 11:53 AM   #10
reinert
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Read post #3 again, and again, and please don't make the mistake of comparing modern pistols and loads to anything relating to black powder firearms; just don't. Shoot your pistol, or rifle for that matter, over some fresh snow sometime, and you'll see the unburned powder laying out there from an overcharged load. If you can't find any snow, law an old white bedsheet out in front of the muzzle and check that out after shooting an overloaded charge. Try it, the unburned stuff will be there. An ODG once said that the best load for a black powder firearm is when ALL the powder is burned from a shot, and no more than that (wasted powder; what's the point?). Another ODG said that half the ball's weight (patched round ball talk here) is a good starting point for a RIFLE'S load. Work up or down on a charge from there. Again, just a comment regarding the use of BLACK POWDER.

I've got a .54 cal. flint pistol with a 6" barrel that shoots very well using 30 grns. of 2FG standard GOEX. I've never shot the pistol over the snow to check for unburned powder, and with a patched ball weighing 230 grns., my charge is WAY, WAY less than half the ball's weight, but again, it shoots very well. I use that same .54 ball in my flint rifle and have found that 80 grns. works very well in it, with wonderful accuracy, and with enough punch to shoot through a whitetail deer at 80 yds. standing BROADSIDE through both lungs (did that a few times). To me, it's what works, and what has worked for all the good info I've gotten through the years from fellow black powder shooters/hunters who've always loved to share info, especially after a hunting season. And I always shared mine...

I've been shooting both flint and percussion, traditional styled rifles since 1975, and have used nothing but black powder and the patched round ball in doing so, EXCLUSIVELY; no Pyrodex, no anything else except the good ol' standard GOEX powder (2 and 3fg), and now lately, I've been playing with Swiss 1.5fg). I've had wonderful, fine friends through the years that have shared info and history on black powder firearms; some have "gone home," and I cherish the ones I still have. Matter of fact, I'm going to shoot with some of the "Old Guard" this weekend!
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Old February 22, 2021, 09:09 AM   #11
bladesmith 1
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When shooting pistol at Friendship we always used 20grs at 25yds and 25 at 50yds [ to keep the same sight picture ]. That was in the 70s, and now 40 some years latter I got the bug to shoot my 1858 Remington revolvers. I chopped the barrel at 3 1/4" and rounded the grip to give me a birds head grip on one of my pistols. I also bought a Taylors 45 Colt cylinder to shoot cartridge shells. It's still fun to shoot cap&ball. This thread kind a got me wondering how much powder to burn, so I guess I'll be loading up 6 shots with different powder charges and shooting over the snow to answer my question. Should be fun.
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Old February 23, 2021, 07:27 AM   #12
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bladesmith1...

Please post the results of your snow-shooting experiment.

I would love to see how lopping off 4 3/4 inches (assuming you started with 8”) affects your optimal charge.

Thank-you... and have fun...!!
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Old February 24, 2021, 08:42 AM   #13
bladesmith 1
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Maybe I didn't do it right, but I didn't see any left over black powder on the snow. I went from 20grs to 25, 28, 30, and then 32grs. I was using a wafer of beeswax/paraffin between the powder and ball so the last charge had to be beat in with a hammer. I was also quit pleased with how clean everything was. Bore, cylinder, axle, and frame all had almost nothing to clean off. It sure beats the way I use to shoot 40 years ago with the lube on top of the ball getting splattered all over. The weather is warming up so the snow is gonna disappear and if I want to try this again I'm gonna have to hurry.
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Old March 10, 2021, 08:54 AM   #14
4V50 Gary
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Accept it. With a flintlock, it's inevitable that there will be some pressure lost as gases vents out the touchhole. Same thing happens with muzzle loading cannons. I will concede this is one advantage cap guns (including inlines) like Minie Rifles do have a slight dedge over flintlocks, wheellocks or matchlocks. While there still is some gas escaping from a cap gun, it's not to the same extent as with a smokepole with a touchhole.

Want superior gas sealing? That's what BPCRs are for. That brass cartridge seals the breech.

I can't find the video, but someone tried to make a 155 mm howitzer shoot a shell loaded with black powder and a fuse. Of course this compromised the gas seal and the gun went KaBoom. Not that big black powder guns can't be made. The 18" at Fort Rinelli (Malta) was a muzzloe loader with one hoist to deliver powder and the other the shell.
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