Obturation of a patched round ball...real or imagined?

[M. De Land]

I do know for a fact, when I was a kid, that grass frogs we used to shoot out of a one inch bore BP cannon surely did obturate............... into mush but they would sometimes make it through and pine board.
Inquiring minds wanted to know!

 

[coloradoclyde]

:thumbsup: Don't forget to record the BHN of the lead balls as hardness is a key factor..... chronograph measurements would also be useful.

 

[Walks with fire]

The ball upon ignition will become shorter from the front to the back (powder side) and will expand it's width. The speed of acceleration from the point of rest is the cause of this. The explosion of the powder does contribute but it's the acceleration that produces the most of it. It can only expand into the grooves so much because of the patch material filling them. The faster the acceleration the more the G force and the more deformation of the sphere there is. Lead will not spring back like some other materials. The G force is making the back of the ball attempt to reach the front of the ball.

With a normal big game charge the ball is going from a complete standstill to well over 1000 miles per hour in the length of the barrel. It's amount of obturation is restricted and contained to the diameter of the bore and the material surrounding the projectile. I believe Roundball's brass ball would obturate at these speeds as well.

To feel the affects of G force find someone who owns a Corvette and have them punch it from a standstill to just 180 miles an hour and you will feel the affects of G force on your body. You will believe that a lead ball in your muzzleloader is indeed experiencing obturation when it's going 1200 miles per hour down the length of your barrel.

High speed video and computer measurement would be the best way to prove or disprove the theory. Much like what was used in the golf ball video.

 

[cynthialee]

Oh look...it is this old :dead: again!

Does it change any single thing any of us do when we shoot? At all?

At the end of the argument we are still gonna do things the exact same way we did it yesterday. There is nothing this argument can change in regards to how we shoot or load.

Obturation of a roundball is not a topic that means a hill of beans at the end of the day. maybe they do, but maybe they don't.
Only situation where obturation of a projectile is important in BP shooting is when we are shooting conicals.

 

[tenngun]

:thumbsup: :hatsoff:

 

[roundball]

I believe Roundball's brass ball would obturate at these speeds as well.

:grin: ...unfortunately, "I believe" is speculation, theory, etc.
But post firing / recovered balls / dial caliper measurements is clinical reality.

The rock hard solid brass balls were still the same manufacturing dimensions as when they started.
100grns Goex 2F, tight fitting patch combo, 38" Rice barrel.

I have no dog in the fight...simply introduced actual facts into the thread.
:wink:

 

[azmntman]

...after more consideration one would have to use a spurless ball to tell if the dead deer, whether he fell on the left or the right of the trail was caused by this phenomenon. If the ball was loaded with the spur tilted slightly left or slightly right the argument that the spur had a bit to do with the right or left falling down dead on the side of the trail could corrupt the study. :youcrazy: :slap: :yakyak: :surrender: :redface:

 

[roundball]

PS:
Have also shot a few hundred of these lightweight solid glass/acrylic marbles out of .58 and .62cal rifles...no obturation / change in dimensions.

 

[azmntman]

Ever slice your gums when chewing the venison? :rotf:

 

[M. De Land]

So if you don't want to discuss wither or not it occurs why discourage the rest of us who do?
Is your opinion any more worth while for us to listen to than ours is for you?

 

[Larry Pletcher]

Permit me a few comments about this discussion.

First I agree with the writer who said that the answer to this will not change the way we load our guns or alter any of our techniques. The answer really doesn't matter, except I am motivated by the challenge it presents - can I develop a methodology to find out.

I dislike making a statement I can't back up with numbers, but here goes. My gut says that if obturation is found, it will not occur in all situations. The key to this is a comparison to two competing forces. One is the resistance to movement of a tightly patched ball and the other is the force required to upset the the ball. For the ball to upset, the resistance to movement must be great enough to hold the ball in place while the force behind the ball begins to deform it.

If the ball bumps up, my gut says that it will need a very tightly patched ball, a stiff load behind it, and perhaps a finer grained sporting grade powder produce a sharper pressure spike.

I'm trying to avoid taking a position until I can provide numbers.

Regards,
Pletch

 

[azmntman]

Make sure spur is pointed straight ahead during testing :blah:

 

[George]

Pletch, I think you will find that inertia is the more important factor, much more than the friction of a tight fitting ball. Smack a pure lead ball suspended in air, touching nothing, and it will be upset by the blow because of inertia. I've always thought we very much underestimate the forces generated by the simple resistance to movement, ala Newton.

Spence

 

[George]

I've always wondered what it is like to have zero curiosity about the world we live in and how it works. What say ye?

Spence

 

[coloradoclyde]

The ease with which a metal can plastically deform is quantified in metallurgy by ductility, defined as


fracture length - original length
----------------------------------------
original length

The conventional concepts of ductile & malleable are both manifestations of metallurgical ductility. The opposite of ductility is brittleness

Other notable material properties of metals are stiffness, yield strength and hardness. Like ductility/brittleness, these properties are all related to the way a metal responds to stress. Stress (force per unit area) can result in strain (deformation). The stress of a person standing on a diving board results in the strain seen in the bending of the board. Deformation can be either elastic or plastic.

For small amounts of stress a metal is completely elastic ”” stiffness is another term for modulus of elasticity (Young's modulus). Stiffness is due to the resistance to separation between atoms ”” the interatomic bonding force. Stiffness diminishes with heating and increases with cooling. (The coefficient of thermal expansion ”” the amount by which length or volume increase with increasing temperature ”” is similarly a function of interatomic bonding energy.)

For large amounts of applied stress a metal will deform permanently (plastically) rather than elastically return to the original shape. The amount of stress just beyond the threshold of plastic deformation is called yield strength. Yield strength varies inversely with grain size ”” smaller grains mean greater yield strength.

When a metal plastically deforms, the manner in which it does so is by the formation and propagation of flaws (dislocations) within the crystal grains. Grain boundaries resist crystal propagation of dislocations, which is why smaller grain size increases yield strength. The dislocations themselves resist further dislocation ”” a phenomenon known as strain hardening. When a blacksmith pounds on a horseshoe, he or she is making the horseshoe harder by increasing the number of dislocations and reducing grain size.

With enough stress a metal will acquire as many dislocations as it can handle without weakening ”” a level of stress described as ultimate tensile strength. Ultimate tensile strength is directly related to the hardness of the material. (Diamond is the hardest substance.) With further application of stress, the dislocations in the metal merge to form tiny fissures which grow into larger cracks until the metal finally fractures.

 

[coloradoclyde]

Here you go Bill...decades of testing with multiple accounts.

Recommended reading.
https://books.google.com/books?id=...bullet's flight from powder to target&f=false

 

[Walks with fire]

It's not supposed to be an argument; it's a discussion. No need to contribute if you wish not to.

 

[Walks with fire]

Thanks for the book link. Looks like some good reading this evening.

The donkey is dead.

 

[Walks with fire]

Some people don't care how it works as long as it works and that's ok. That's why there are car mechanics and fast food restaurants. :grin:

 

[Okie Hog]

Colorado Clyde:

Thanks for the book link.

BTW: They attributed the obturation effect to "the boot of the black". The bullets of some of the early blackpowder handgun cartridges failed obturate when those cartridges were later loaded with smokeless powder.