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

[coloradoclyde]

Then we are in agreement? yes?

 

[George]

Shooting 2 balls w/ a heavy powder charge and also references to cast lead bullets shot in CFs aren't pertinent to the topic.

There are people who believe BP pressures are too low to deform pure lead. The picture may or may not show "obturation" in the sense we use it in these discussions, but at least it shows that deformation can and does take place at BP pressures.

Spence

 

[coloradoclyde]

references to cast lead bullets shot in CFs aren't pertinent to the topic.

I believe they are when talking about lead bullets, casting and obturation. They provide contrast reference data. lead bullet data from C.A.S. has many direct similarities....the bullets are lead, and the velocities are based on BP loads. sometimes they are BP loads.

 

[roundball]

Then we are in agreement? yes?

No...you're spending so much time high-jacking and crawfishing you're off the point of the thread, which asks about obturating under firing.

 

[coloradoclyde]

Some people don't believe that a ball or bullet will obturate when fired....but we can establish that it can be obturated during loading...and there seems to be no disagreement on that part.
So the challenge becomes distinguishing between the two...How do we establish obturation from firing if it has already been obturated?

1. establish a loading method that does not obturate the ball.

2. establish a bullet recovery method that does not obturate the ball.

3. fire the projectile.

4. Compare .


This is a simple experiment that any of us can perform.

 

[Vaino]

Have shot and cast many lead bullets for CFs....the "lead" is an alloy of lead, tin and antimony and not comparable to the soft lead used in RBs for MLers.

After shooting CFs and trying for ultimate accuracy, w/ all it's technical aspects, the shooting of MLers is so easy and uncomplicated and seeing MLers produces excellent accuracy so easily, I prefer to not complicate my shooting.



So if RBs did compress from pressure when fired and increased in dia...so what? The miniscule amount of dia increase doesn't amount to that much and certainly doesn't affect the sealing off of the grooves where if there's leakage, that's where it will occur.....Fred

 

[tenngun]

Get a barrel you could debreech, I have never pulled a plug on one after I finnished installing the tang/barrel inlet. Had a morry . 50 and thought you had to debreech to clean.
Onward, load your ball load and run it down the barrel, mich it at the bottom when it pops out. Reasemble the gun. Find some one in the country that has an outdoor back yard free standing pool. Load and shoot in to the water from near the surface, ball will lie on the bottom. Forensic investigator shoot water tanks to get an undamaged bullet. Mich the ball again??? Did it change, more then loading, was some change caused by hitting the water? :idunno:

 

[coloradoclyde]

The affects of obturation are used in forensic firearms identifcation by crime labs all across the country, and is defined as:
Obturation
1. The sealing of gases due to the expansion of a cartridge case as a result of chamber pressure.

2. The sealing of gases due to the expansion and/or upset of the bullet base as it travels down the bore.

Office of Law Enforcement Standards National Institute of Standards and Technology

 

[Walks with fire]

Whanging the ball has be shown to increase velocity and accuracy in some tests. It also had the lowest standard deviation. Upset of pure lead doesn't take much pressure and ignition creates pressures sufficient to do that IMO.

Would a heavier projectile create more resistance and thus more expansion? I believe it would. Would a tighter load combination seal the bore more and contain the pressure more effectively and possibly lead to more upset?

 

[Ron_T.]

A RB obturates the bore because of the patch thickness...the amount of obturation depends on how completely the bore is sealed due to a sufficiently sized RB/patch thickness combination.

As far as the RB compressing and thereby increasing its diameter and adding to the total bore seal...don't think there's enough resistance to compress the RB even when caused by inertia which is evident because of the pressure "spike" and the resistance becomes a lot less as the PRB proceeds down the bbl.

Minie ball skirts are flared out to seal the bore and do this when inertia causes a pressure spike which is the highest pressure that will be evident during the Minie ball's trip down the bbl.

The TC Maxiball is supposed to obturate the bore more tightly because of the inertial pressure spike causing the smaller dias in between the bore dias to compress thereby increasing the dias of the larger flats that ride in the bore. TC says this happens and maybe it does or doesn't.

Black powder w/ its much lower pressures isn't capable of compressing a lead RB from a practical standpoint in my opinion....even at the inertial pressure spike......Fred

*******************************************

I agree with Fred 100%...

That said, one must realize that in order to perform "total obturation", the obturation of a black powder, muzzle-loader's patched, lead ball is totally dependent on a tight-fit, patch-to- bore, to keep the powder's gases mostly or, ideally, completely behind the patched rifle ball since the round lead ball is somewhat smaller than the full diameter of the rifle's bore.

Thus, under ideal conditions, the patch must fit the overall bore tight enough to keep all the powder's pressure/gases behind the round, patched ball until the ball leaves the rifle's muzzle.


Strength & Honor...

Ron T.

 

[George]

So if RBs did compress from pressure when fired and increased in dia...so what? The miniscule amount of dia increase doesn't amount to that much and certainly doesn't affect the sealing off of the grooves where if there's leakage, that's where it will occur.....Fred

Any increase in diameter can't be anything but good. Most of us agree that a tighter patch-ball combination is more accurate, and we go to extremes sometimes to load such a combination. I agree that ball upset doesn't fill the grooves, but I do believe it occurs and is a help in improving the seal.

I've never been able to understand how anyone can look at that double ball picture and still doubt that lead roundballs upset.

Spence

 

[roundball]

Some additional information to make the point that PRB accuracy has no dependency on "obturating" into rifling grooves, are the 2012 tests I ran using rock hard solid brass balls when researching non-lead ball alternatives in case lead became banned.
(July 2012 full range report details are posted here on the MLF)

Used these .5625" balls in my .58cal Early Virginia, deadly accurate at the range.
Then after finding the once fired balls still mic'd to their original dimensions, I REUSED them for deer hunting, took deer with them, worked perfectly...in spite of zero obturation.

 

[azmntman]

To sum it all up...they may or may not but it doesn't matter. Like if yur deer falls on the right of the trail or the left. The deer is dead and the meat tastes the same no matter if the ball did or didn't or which side he fell.

I dont care much but if it was on a test I would guess they didnt. I would also guess the deer fell on the left side. :shake:

 

[Rifleman1776]

I've never been able to understand how anyone can look at that double ball picture and still doubt that lead roundballs upset.

That Lyman pic is famous and infamous.
I doubt it proves anything. The flattening could have been the result of grossly excessive pressure when loaded. It could be the result of the two balls colliding on ignition. And, I suspect that to be the case.
Tenngun is right, the water tank catch might be the only way to prover or disprove this ancient, never-ending :yakyak: obturation discussion.

 

[coloradoclyde]

The flattening could have been the result of grossly excessive pressure when loaded.

How do you explain the sprue then???

The balls flatten more in between each other because there is very little contact area there to dissipate the pressure,(this magnifies the pressure) there is also a void where the lead can expand.
The bottom of the bottom ball does not flatten on loading because it is cushioned by the powder and when fired the gas pressure is distributed evenly over the arced surface.
The presence of a sprue indicates that it was not forcefully loaded.

 

[coloradoclyde]

Tenngun is right, the water tank catch might be the only way to prover or disprove this ancient, never-ending obturation discussion.

The same method used by forensic ballisticians.

 

[coloradoclyde]

Gentleman here is a short video to help you grasp some of the physics that related to this discussion.....its not a bullet but serves as a good stand in. I hope you find it as enlightening as I did..

https://youtu.be/aMqM13EUSKw

https://youtu.be/6TA1s1oNpbk

 

[M. De Land]

I'm sure they obturate because they are no longer round when they leave the bore and are in flight.
I 've seen this before in pictures of balls in flight, the sides are straight at the ball waist for a small distance and it will be the same with a light patch which means it wasn't put there by loading pressure.
The sides will now be parallel to the bore for a certain distance/length all the way around.

 

[Skychief]

I'm willing to bet, that, should some alien force "beam me up" at an acceleration rate that got me moving 2000 feet per second in the first 3 or 4 feet above the recliner in which I now sit,.......l would surely obturate! :shocked2:

Maybe I'm squishier than a lead ball. :haha:

:idunno: , Skychief.

 

[Larry Pletcher]

I have thought about this experiment for quite a number of years. In fact I believe Spence and I discussed this on a former list. I believe I have a way to measure this, however It requires solving a couple problems.

To summarize, one needs to load a ball with enough extra patch to pull it back out. By measuring the length of the of the clothe impressions and measuring the length of the ball, we can tell the amount of deformation is caused by the loading process. (This part is not difficult.)

The second problem is more difficult. One needs to either recover the ball without causing deformation or measure the ball some other way. The problem of recovering the ball with NO deformation is impossible to prove IMHO. One could not logically state that any difference was caused by firing the ball or recovering the ball.

The only way to completely remove recovery deformation is to look at the ball before it impacts the bullet stop. There is a way to do this using photography with an extreeeemly short duration flash - here I'm talking about a duration of 1/10,000,000 of a second. A flash of this type has stopped a projectile traveling 2800 feet/second, allowing rifling marks to be measured.

Using this method one would load the ball, fire it, and photograph the ball just after the patch separates. If obturation takes place, the rifling marks on the ball should be longer than the ones on the ball loaded and pulled. If the rifling marks are unchanged, obturation did not take place.

I have photographed a ball traveling 1000 feet/second but have not done this at a velocity necessary to prove or disprove the theory. My current flash is not capable of the short duration necessary to do this. The flash required is available but expensive. Eventually I expect to do this test. Bear with me a bit; I'll have to save a bit of money, but this type of experiment is what I really like to do.

Regards,
Pletch