Frontier's
Buckskins & Black Powder
All of today's technology and this myth of a round ball expanding, still exists?
Round balls and obturation
- Thread starter longcruise
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Yes, the fundamental principles of physics are extremely persistent and do not require faith, understanding or observation to exist.
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Frontier's
Buckskins & Black Powder
longcruise
70 Cal.
@Deavertex You are clearly explaining what my little arrows meant. The pressure surrounds anything that has a surface exposed to it. That point at the center of the bottom of the ball is under the same pressure as the entire underside surface of the ball. Above that centerpoint is the centerpoint of the top of the ball and between is the mass effected by the crushing action of the of it's own weight and inertia. It would seem then that that portion of the ball would bump up like a conical slug. But it still has all that pressure applied around the entire exposed bottom surface of the the ball. That pressure is offsetting the vertical pressure and forcing the ball to remain round.
I have no engineering background. I are a sociologist!
But I have blown up enough birthday party balloons to have some understanding.
I have no engineering background. I are a sociologist!
But I have blown up enough birthday party balloons to have some understanding.
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It's my understanding that it is not pressure/gases that hits the back of the ball, but is indeed a solid slug of compressed gunpowder.
Physics demands that the back of the ball starts moving before the front.
Physics demands that the back of the ball starts moving before the front.
longcruise
70 Cal.
That's an interesting thought.
Rock Home Isle
58 Cal.
Absolutely, the shape of the projectile is not going to change the properties of the material from which it’s made.
Your sketch depicts the beginning of a Free Body Diagram, a fundamental tool to describe forces on an object. You are on the trail of an explanation. As a mechanical engineer I've drawn hundreds of them. To get the correct solution you must account for everything. Gas pressure in front of the ball will have an identical distribution of force vectors at lower magnitude. The large missing force in your diagram is the acceleration force, coaxial to the bore through the center of the ball. Sliding friction force will act in the same direction, opposite to ball velocity. The summation of all these forces is zero, the basic equation that solves for unknown variables. Summarized resultant pressure force vectors act opposite to the F = mA acceleration force vector to compress the ball. The ball will expand laterally by Poisson's ratio, approximately. There are many non-linearities in this analysis, making this explanation valid for only one instant in time. It does explain in simple terms why a soft ball obturates when briskly accelerated.
longcruise
70 Cal.
Well, your explanation is waaay above my pay grade!
but that one instant in time is what I'm addressing. BP, creates a sudden and explosive instant. If the projectile is going to bump up and obturate the bore it's going to happen in that instant of ignition that my drawing illustrates. But it doesn't. In every slo mo picture or video I have seen considerable flame precedes the balls exit from the bore. It's passing between the ball and the bore. Therefore, the bore is not obturated.
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.570 prb 120gr of 3fffg Eynsford.
longcruise
70 Cal.
What do you think this tells us?
Imagine the breech facing side of the ball being smacked, in an instant, with a bore sized pressure hammer of 20,000 psi …starting the “rear” of the ball down the bore slightly before the “front” of the ball ( because of its inertia to remain at rest)… lead having little ability to spring back to shape, obturates ever so slightly whatever amount it can, compressing the patch material tighter into the rifling and grooves.Well, your explanation is waaay above my pay grade!
How ever slight the ball deformed by the smack of the powder column or expanding gas pressure…it still deformed / obturated…and pictures perhaps would not show the mere thousandths that it changed shape.
longcruise
70 Cal.
I think That's fully considered in my diagram. The arrows depict that same 20,000 # of pressure acting to squeeze the ball back to center or IOW, keeping the ball in a round shape. That pressure also seems to be exerting against the side of the ball as it travels between the ball and the wall of the bore.
Question for Freedom - how did you recover that ball? It had to be shot into something I would think.
Wondering the same also. Don't know how many times I've dug around in the dirt behind target stands looking for fired balls, with RSO's casting inquiring glances my way. "Watcha looking for, dude?!?!"
I picked up some from below a swinging steel plate. They were obturated really well.
Deavertex
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The back does indeed start moving before the front by a tiny bit of time, but there isn't a solid slug of compressed gunpowder. That stuff all burns, and any that hits the back of the ball will be burned before the ball is out of the barrel. It's not momentum, but a pressure differential on the two sides of the ball that make it move.
Deavertex
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I believe what you're seeing is some gas that escapes around the ball before it obturates fully. The ball in a muzzle loader doesn't HAVE to fully obturate to work, but the more it completely fills the bore and rifling, the higher the velocity, and that results in a flatter trajectory and more muzzle energy.Well, your explanation is waaay above my pay grade!
There is that Newton guy that screwed up the whole understanding of physics.
Things don’t like to move, so when a force tries to move it it resist, and that resistance changes shape of the object.
If you use short starter or a knife handle to thump the ball in to the muzzle you change its shape
When you ram it home you change its shape
How much does a barrel weigh? Three four pounds. Does it vibrate when you shoot? We know it does,
We don’t give a second thought to resonance
A powder charge can shake a barrel of several pounds, but won’t change the shape of an half ounce lead ball
Right
How much does it change is covered by too many factors, ball weight, powder charge, ambient temperature, tightness of the load…..
But it can’t help but to change its shape
Lay a ball on a sheet of ice, thump it with your finger nail, and that ball will change shape before it moves
Things don’t like to move, so when a force tries to move it it resist, and that resistance changes shape of the object.
If you use short starter or a knife handle to thump the ball in to the muzzle you change its shape
When you ram it home you change its shape
How much does a barrel weigh? Three four pounds. Does it vibrate when you shoot? We know it does,
We don’t give a second thought to resonance
A powder charge can shake a barrel of several pounds, but won’t change the shape of an half ounce lead ball
Right
How much does it change is covered by too many factors, ball weight, powder charge, ambient temperature, tightness of the load…..
But it can’t help but to change its shape
Lay a ball on a sheet of ice, thump it with your finger nail, and that ball will change shape before it moves
