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Thread: Volume of TC patent breech

  1. #1
    Boolit Buddy

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    Volume of TC patent breech

    Does anyone know how much volume it takes to fill the flash channel and cone of a Thompson Center patent breech with powder? Just eyeballing, it looks like about 30 grains. I'm hung up on really light loads and wonder if I put in too little powder to fill the space behind the ball, and air space results, will it be a problem? Or would the pressure of such light loads be too little to matter? A theoretical concern, I know - maybe not a practical one - but I would be interested in your thoughts on the matter.

  2. #2
    Boolit Grand Master Nobade's Avatar
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    It depends on caliber but I don't think it's nearly that much. Probably closer to 10 grains.

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    Good question. I think I have one in the shop I cut off a barrel, I'll try to remember to check.

    It appears to be around 12 grains. The way they hogged out the end, I would suspect it could go 2 gr. either way depending on individual gun..
    Last edited by waksupi; 08-30-2021 at 08:00 PM.
    The solid soft lead bullet is undoubtably the best and most satisfactory expanding bullet that has ever been designed. It invariably mushrooms perfectly, and never breaks up. With the metal base that is essential for velocities of 2000 f.s. and upwards to protect the naked base, these metal-based soft lead bullets are splendid.
    John Taylor - "African Rifles and Cartridges"

    Forget everything you know about loading jacketed bullets. This is a whole new ball game!


  4. #4
    Boolit Buddy

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    Thanks guys! Very helpful. I expect that I should not worry with any loads over 20 grains. Bill

  5. #5
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    Wouldn't this depend on caliber? I'm assuming the 32 caliber is a much smaller plug than a 54.

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    Boolit Grand Master pietro's Avatar
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    I would think that you needn't worry about light loads creating an air gap between the powder and the projectile if you drop a little dry Cream of Wheat atop the powder charge B 4 seating the projectile.

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  7. #7
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    Yes, caliber dependent. For the typical .50 to .54 I wouldn't load less than 30 grains by volume.

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    As a follow up, no there is not a minimum load. I've dry balled more than once, and only fit a few grains behind the ball. No danger at all. The fear of airspace is the most overrated thing in all of blackpowder. No, I wouldn't intentionally short start a ball, but a 1/4" gap is not going to cause some kind of magic pressure wave.

  9. #9
    Boolit Buddy

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    Thanks to all for your input. Your interest and response is appreciated. Bill

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    Boolit Grand Master bedbugbilly's Avatar
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    I would like to address megasupermqgnum's post about BP and air space between powder and projectile - and in no way am I being critical of his post - just passing this along.

    I have been shooting BP now for close to 60 years - revolver, smoothbore, rifle, rifled musket, cannot and mortars - I have even shot an original Gatling Gun - not that any of it makes me an "expert" - just fortunate to have had a lot of varied and interesting experiences. One thing that was ALWAYS hammered into anyone's head who shot
    BP was "never leave an air space" - and honestly - I think that anyone who has shot BP knows that rules.

    Many years ago, I belonged to a group of "cannoneers" - we had two full sized South Bend 10 Pounder Parrott Riofle replicas - one rifled and one a smoothbore - South Bend had a raffle one time and one fo the guys in the group just happened to with the smoothbore that they raffled off. Anyway . . . we cast and shot aluminum balls in the smoothbore - had a go/no go gauge that we would put them through just like the original ones were checked. We were up at the National Guard Range at Grayling, MI for a shoot one weekend - cannons, mortars and then a day of long range rifled musket - a fun time. As we were loading and firing the smoothbore ten pounder, we got a ball stuck half-way down the barrel - the guy who cast the balls and who was supposed to check the with the gauge didn't check them. OK - here we sat with a 1 pound service charge of cannon grade powder under a ball that was stuck half way down the barrel. It wouldn't go down and we couldn't use the worm to remove it.

    One of the fellows there, Matt Switlock, who had extensive experience with a wide variety of artillery pieces, came over and we had a "pow-wow". I knew Matt as did the others - a really good fellow. We talked about how to proceed with the stuck round and he began telling about a study he had just read about the British Navy who conducted experiments and studies in the 1700s concerning the very same thing we were faced with as related to their Naval cannons aboard ship. He stated that the study had shown that just because the ball was stuck halfway down the bore - their study had proven that it wasn't a sure fire castrophe or that the tube would blow up if the charge was set off.

    We didn't want to haul the gun home with a charge and stuck ball in it so we mutually agreed to give Matt's research and conclusions a chance. We wheeled the bun well ahead of the berm that bordered the particular range - got everyone behind it and I agreed to go out and prime the gun with a friction primer and use a very long lanyard to set it off. We all were very aphrenrsive about it and I'm sure we all had visions of blowing the tube up and losing a nice cannon. I laid down, yelled "fire in the hole" and everyone ducked below the berm behind us. The layyard was long so it had a lot of "give" - but on about the third strong tug on it, the friction primer went off. I expected a much louder than normal "boom" - but to our surprise - the 1 pound service charge went off with a boom and it was almost like a "hang fire" - as a split second after the initial explosion of the powder, there was a loud "thunk" and everyone's head was above the berm watching the 3" aluminum cannon ball as it spit out of the end of the barrel. We didn't have a whole lot of elevation on the barrel but we could clearly see the ball as it exited and went down range, veering to the right until gravity took over and it bounced along the ground.

    We all learned a LOT that day - and there were a lot of us there that were experienced BP shooters. Now . . . I'm certainly not advocating an air space between BP and a projectile - it's a "cardinal rule" not to have an air space and it's something we all need and should want to follow - whether in a muzzleloader or BP cartridge loading - but as megasupermqgnum points out - and I know I have done it over the years when I have had a stuck ball not fully seated - what do most do? Remove the nipple and work some powder down into the chamber - or even remove the vent liner on a flintlock and do the same - then touch it off to get the ball out. Not a whole lot different that using a high PSI pressure to eject a stuck ball - although I would surmise that the compressed PSI of air might be a bit less than a small loa of powder worked into the chamber and then set off. I have no doubts that our ancestors faced the same thing at times - a stuck ball in a barrel when they were in the woods or on the prairies miles from anywhere and the only option they had was to work some powder in through the breech and touch it off - and most of those barrels had coarse thread breech plugs and it would be questionable as to whether the barrels were of the same quality of what we have today.

    In the end - it's wise to live by the "cardinal rule" and we can all agree on that I'm sure - be safe above all else. And, when you get that ball "stuck" . . . or you dry ball a rifle . . . just know that if you do much shooting at all, at some point it is bound to happen.

    As far as the powder capacity of the chamber in a patent breech plug goes - just remember that not all patented breech plugs are created equal. The only real way to know what your particular breech plug powder capacity is would be to remove it and check it. If it is a modern "production rifle" - then probably it is fairly consistent from one rifle to the next IN THE SAME CALIBERR. Over the years, I have worked on a lot of original rifles with patent breeches and even on rifles of the same caliber barrels, the powder capacity of the breech plug could easily vary - so if you have an original rifle - check it out and don't go by what a modern production rifle has.

  11. #11
    Boolit Grand Master Good Cheer's Avatar
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    I've only had one ringed barrel in my hands, sold to me by someone who somehow failed to mention what he'd done. So, I know a pressure wave can do strange things if all the circumstances are right. It can even bend character.

  12. #12
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    Quote Originally Posted by bedbugbilly View Post
    I would like to address megasupermqgnum's post about BP and air space between powder and projectile - and in no way am I being critical of his post - just passing this along.

    I have been shooting BP now for close to 60 years - revolver, smoothbore, rifle, rifled musket, cannot and mortars - I have even shot an original Gatling Gun - not that any of it makes me an "expert" - just fortunate to have had a lot of varied and interesting experiences. One thing that was ALWAYS hammered into anyone's head who shot
    BP was "never leave an air space" - and honestly - I think that anyone who has shot BP knows that rules.

    Many years ago, I belonged to a group of "cannoneers" - we had two full sized South Bend 10 Pounder Parrott Riofle replicas - one rifled and one a smoothbore - South Bend had a raffle one time and one fo the guys in the group just happened to with the smoothbore that they raffled off. Anyway . . . we cast and shot aluminum balls in the smoothbore - had a go/no go gauge that we would put them through just like the original ones were checked. We were up at the National Guard Range at Grayling, MI for a shoot one weekend - cannons, mortars and then a day of long range rifled musket - a fun time. As we were loading and firing the smoothbore ten pounder, we got a ball stuck half-way down the barrel - the guy who cast the balls and who was supposed to check the with the gauge didn't check them. OK - here we sat with a 1 pound service charge of cannon grade powder under a ball that was stuck half way down the barrel. It wouldn't go down and we couldn't use the worm to remove it.

    One of the fellows there, Matt Switlock, who had extensive experience with a wide variety of artillery pieces, came over and we had a "pow-wow". I knew Matt as did the others - a really good fellow. We talked about how to proceed with the stuck round and he began telling about a study he had just read about the British Navy who conducted experiments and studies in the 1700s concerning the very same thing we were faced with as related to their Naval cannons aboard ship. He stated that the study had shown that just because the ball was stuck halfway down the bore - their study had proven that it wasn't a sure fire castrophe or that the tube would blow up if the charge was set off.

    We didn't want to haul the gun home with a charge and stuck ball in it so we mutually agreed to give Matt's research and conclusions a chance. We wheeled the bun well ahead of the berm that bordered the particular range - got everyone behind it and I agreed to go out and prime the gun with a friction primer and use a very long lanyard to set it off. We all were very aphrenrsive about it and I'm sure we all had visions of blowing the tube up and losing a nice cannon. I laid down, yelled "fire in the hole" and everyone ducked below the berm behind us. The layyard was long so it had a lot of "give" - but on about the third strong tug on it, the friction primer went off. I expected a much louder than normal "boom" - but to our surprise - the 1 pound service charge went off with a boom and it was almost like a "hang fire" - as a split second after the initial explosion of the powder, there was a loud "thunk" and everyone's head was above the berm watching the 3" aluminum cannon ball as it spit out of the end of the barrel. We didn't have a whole lot of elevation on the barrel but we could clearly see the ball as it exited and went down range, veering to the right until gravity took over and it bounced along the ground.

    We all learned a LOT that day - and there were a lot of us there that were experienced BP shooters. Now . . . I'm certainly not advocating an air space between BP and a projectile - it's a "cardinal rule" not to have an air space and it's something we all need and should want to follow - whether in a muzzleloader or BP cartridge loading - but as megasupermqgnum points out - and I know I have done it over the years when I have had a stuck ball not fully seated - what do most do? Remove the nipple and work some powder down into the chamber - or even remove the vent liner on a flintlock and do the same - then touch it off to get the ball out. Not a whole lot different that using a high PSI pressure to eject a stuck ball - although I would surmise that the compressed PSI of air might be a bit less than a small loa of powder worked into the chamber and then set off. I have no doubts that our ancestors faced the same thing at times - a stuck ball in a barrel when they were in the woods or on the prairies miles from anywhere and the only option they had was to work some powder in through the breech and touch it off - and most of those barrels had coarse thread breech plugs and it would be questionable as to whether the barrels were of the same quality of what we have today.

    In the end - it's wise to live by the "cardinal rule" and we can all agree on that I'm sure - be safe above all else. And, when you get that ball "stuck" . . . or you dry ball a rifle . . . just know that if you do much shooting at all, at some point it is bound to happen.

    As far as the powder capacity of the chamber in a patent breech plug goes - just remember that not all patented breech plugs are created equal. The only real way to know what your particular breech plug powder capacity is would be to remove it and check it. If it is a modern "production rifle" - then probably it is fairly consistent from one rifle to the next IN THE SAME CALIBERR. Over the years, I have worked on a lot of original rifles with patent breeches and even on rifles of the same caliber barrels, the powder capacity of the breech plug could easily vary - so if you have an original rifle - check it out and don't go by what a modern production rifle has.
    I wonder if a projectile heavier than aluminum would have had a different result?
    The solid soft lead bullet is undoubtably the best and most satisfactory expanding bullet that has ever been designed. It invariably mushrooms perfectly, and never breaks up. With the metal base that is essential for velocities of 2000 f.s. and upwards to protect the naked base, these metal-based soft lead bullets are splendid.
    John Taylor - "African Rifles and Cartridges"

    Forget everything you know about loading jacketed bullets. This is a whole new ball game!


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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check