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

[M. De Land]

I've seen this type of ball in flight picture before Larry and I can clearly see the waist parallels/obturation in yours as well.

 

[Vaino]

The expanding gases of the ignited powder at some point in time have to overcome the inertia of the PRB and at this time a pressure spike is produced which is the highest pressure that the RB will experience. How much unburnt powder is present behind the PRB at the point of overcoming the inertia of the PRB is difficult to determine.....heavy loads probably have more unburnt powder at the time of overcoming the PRB inertia than light loads. Or....possibly there is no unburnt powder at the time of overcoming the PRB inertia.

Heavy loads destroy patches more so than light loads...so why is this if in a big load the powder acts like a "buffer" that protects the patch?

Whether a PRB compresses and therefore grows in dia. when shot is an unknown, but at any rate, finding out would surely require expensive equipment and a whole lot of time...and for what? The results surely wouldn't cause a change in how people load and shoot their MLers.

How do you measure the dia and "length" of a PRB pushed down the bbl? A properly loaded PRB causes the RB to slightly decrease in dia at its "equator" or circular tangent point...and the displaced lead has to go somewhere, so the RB elongates and its dimension is no longer a dia, but a "length". But how do you measure this to determine any change after firing? Possibly blow out the PRB w/ CO2, but then it would have to be reloaded exactly the same into the same bbl.To do the measurements, the patch would have to be removed and replaced exactly the same.

Perhaps we can interpolate the results from a lead bullet which would be easier to measure, both before and after firing....but are the interpolation of these results valid when applied to a PRB? I don't think so.

Pletch...don't know if high speed photography would produce the accuracy to determine whether the RB increased in dia due to pressure and as explained previously, measuring the RB before and after firing is nearly imposible.

I'm sure I'll ponder all the responses to this topic the next time I use my MLer.....Fred

 

[roundball]

Although I agree w/ most of your post w/ the exception being....."obturation "OF" a patched round ball". "OF" should be replaced w/ "BY". Not being critical, but the definition of "obturate" is to close, seal off or stop up a bore so there's zero gas blow by.

As far as being inquisitive....I've been that all of my working life and still am, but only about things that have some importance.

Whether a RB increases in dia or not when fired isn't of major importance in "obturating" the bore....the patch is responsible for doing this. So if it is a fact that a RB does increase its dia when fired, the amount of increase is small and nearly undetectable.

The most difficult areas of a bore to obturate are the grooves...the areas that the RB and patch do completely seal off are the lands and a small increase of the RB's dia just slightly increases the seal.

I suspect that if many shooters would calculate the patch thickness req'd for the actual bore and groove dias and the RB dia being used, they'd find that the patch thickness isn't sufficient to seal off the grooves.

It would seem that w/ radius groove rifling the patch can more readily seal off the grooves because the grooves don't have sharp corners as w/ flat bottom rifling.

When starting to shoot and hunt w/ MLers, I developed very accurate and efficient loads because I took the time to calculate a patch thickness that sealed off the grooves. Whether or not a RB increased in dia was not considered because from a practical standpoint, it didn't matter. So...how many of you consider a RB's increase in dia or not when fired when determining a suitable patch thickness for a RB's dia?.....Fred

Just to add additional information.
My assumption / understanding of the context of the OP's question was as it relates to the practical functional aspect of a PRB in a muzzleloader.
IE: does a PRB expand / obturate to engage the rifling as part of an intended design / performance expectation.

In close to 25,000+ recorded PRB shots out of many calibers of many muzzleloaders for going on a quarter of a century I have yet to see any evidence of a PRB expanding / obturating in any intended / expected functional manner associated with its purpose of being fired from a muzzleloader. And that includes shooting / recovering PRBs from game, from soft foam trap boxes, from jugs of water, etc.
The conclusion is PRBs do not 'obturate' as part of their designed expected performance to engage rifling...like the skirt of a miniball does.

It is further proven to be crystal clear that there is zero requirement for a PRB to expand / obturate for accuracy given my own personal tests documented her on the MLF, with solid glass/acrylic marbles and solid brass balls...both of which are 'PRBs"...during non-lead projectile testing, both on the range and in the field.

 

[coloradoclyde]

You could use a gun with a removable breech to facilitate post loading measurements.
Keep in mind that if possible we want to exaggerate the affects of obturation so they are easily measurable.
If we create conditions by where we cannot measure the obturation it will not disprove obturation it will only show that we can not measure it.

 

[roundball]

And you're a philosopher too? You're treading on subjects that really aren't at all in "your realm". Your statements as to how people should behave doesn't help in this discussion and only shows...well I'm not qualified, as are you, and we're both certainly not qualified to ascertain how people think and the reasons they think as they do . This discussion is really about "who wins" and ego and the facts are ignored... and you're a contributor to this "winning above all"

I don't think you read other's opposing viewpoints completely or don't digest the meanings of opposing views....this is quite evident in your responses. Seeing this discussion has deteriorated into "winning above all" and for what little contribution I've made to this "discussion". I take partial blame, for it has deteriorated into a controversial but minor subject that from the onset was doomed to be "what it has become".

Up till now I've just offered what I perceive as technical aspects of internal ballistics in a MLing BBl....what you've offered were irrelevant info and personal biases.

This topic should be "locked" before the "fireworks" really start......Fred

Extremely well said.
Unfortunately every forum has a few keyboard hunters / keyboard theorists who seem to post in every thread that appears up and down the forum...but the knowledge level, lack of real hands on experience is obvious based upon questions asked and statements made.

 

[Vaino]

We wouldn't be measuring "obturation" of a fired RB...we would be measuring the dia and length of a RB......obturation is the act of closing off, sealing off or stopping up a bore to prevent gas leakage. This can be done in various ways.....and a PRB is one of them.....Fred

 

[coloradoclyde]

Nowhere in the OP's original comment does he reference round balls being "designed" to obturate.
He referenced minnie bullets being designed to obturate, which is actually a misnomer.....they are designed to make use of obturation.

And you criticized me about reading comprehension :shocked2: :rotf:
I was glad to se you had started talking to me again, but now I see that may have been premature. :shake:

You have made your position of disbelief well known......You can stop trolling now.
There are people who have a genuine interest in this topic.... if your not one of them please find another. :v

 

[coloradoclyde]

Different definition, different criteria, different test......that's ok it doesn't matter just document every aspect of what you do and it will provide good data. :thumbsup:

 

[M. De Land]

The ball shortens and splays out Fred and that is part of the reason for the obturation and side parallels clearly seen in recovered snow balls or in flight pictures.
A portion of this occurs at loading but not all of it.
Heavy loads blow/tear the patches up at the muzzle from unburned powder grain and escaping gas not while in the bore if of proper cloth type (cotton), thickness and weave.
Dr. Mann proved that bullet obturation occurs progressively up bore for several inches with black powder. The highest pressure spike is not necessarily the instant the ball begins to move because the whole powder column is not yet burning but probably shortly there after as overcoming the inertia raises pressure which increases the burn efficiency of the powder column so in the first few inches as more of the column ignites and the internal volume is still small is likely the highest point of pressure.
It can easily be demonstrated that the whole powder column does not ignite simultaneously in a short barreled hand gun or rifle.

 

[Vaino]

Don't understand the first part of your post.......Fred

 

[coloradoclyde]

The ball shortens and splays out Fred and that is part of the reason for the obturation and side parallels clearly seen in recovered snow balls or in flight pictures.

It's like making a quarter....a smooth slug is placed into a die and extreme pressure is applied. The side of the die has ridges just like a barrel has rifling. The pressure expands the slug into the grooves and voila your quarter has ridges on the sides.

 

[Larry Pletcher]

The ability to measure the amount of deformation caused by loading is easy. Load the ball with extra cloth and pull it back out again. The ball will show the cloth marks. Here is something that surprised me. If you mic the ball before and after doing this, you will find that the ball is shorter front to back.

I tried this with three different sizes of balls for my .54 Rice barrel. I measured a .526, a .530, and .535 before loading. Then I loaded each one and pulled it back out. All balls were shorter than they were originally. However, they did have longer contact with the rifling. The .535 ball had the longest cloth mark front to back, and the .526 ball had the shortest. I expected the .535 ball to grow in length, but instead it simply grew a longer "bore-ride" in the center.

When working with a single size ball, I would expect this type of deformation if obturation took place. If none took place, I would expect to see the same measurement as noted on the loaded and pulled ball.

Regards,
Pletch

 

[Vaino]

The displaced lead from compression when loading a PRB has to go somewhere.....I suspect it migrates to the grooves. Normally one would think the "ball" would elongate, but you measured that it became shorter. That's surprising.

Wonder if a PRB when loaded in a smoothbore would elongate since there's no grooves to accept the displaced lead?

How did you pull the PRBs out?....Fred

 

[Larry Pletcher]

The displaced lead from compression when loading a PRB has to go somewhere.....I suspect it migrates to the grooves. Normally one would think the "ball" would elongate, but you measured that it became shorter. That's surprising.

Wonder if a PRB when loaded in a smoothbore would elongate since there's no grooves to accept the displaced lead?

How did you pull the PRBs out?....Fred

I loaded the ball with it in the middle of a sheet of patching. Used a nicely shaped loading tool to prevent smashing the front of the ball. Then I used the patch material to pull it back out.
Regards,
Pletch

 

[Larry Pletcher]

Fred,
I hunted through some notes trying to find the numbers for that .526, .530, .535 ball "load and pull" thing. So often I file something away and can't find it. So I got out the .54 and three ball sizes and repeated the experiment. Below is what I got tonight:

----------Before loading--After pulling------front to back
Ball size-----F to B dia-----F to B dia-----length rifling mark

.526---------.5255-----------.5235-------------.141
.530---------.5305-----------.526--------------.163
.535---------.5365-----------.527--------------.172

I always have trouble formatting a chart. I hope the dashes work. BTW, I used the same cloth for all three balls. Pulling the .535 was hard the last time I did this and was hard to pull this time also. I worried about tearing off the cloth and having to trickle in some powder, seat the ball, and shooting it out. That wouldn't be hard to do, but it would ruin the experiment.

Regards,
Pletch

 

[Vaino]

Your chart is excellent and the info is really surprising. As the size of the ball dia increased, so did the shrinkage, front to back. The .523 ball shrunk .002, the .530 shrunk .0045 and the .535 ball shrunk .0095.Your results have been verified a second time....so must be accurate.

Good way to pull the ball w/o damage. Thanks, Fred

 

[M. De Land]

I suspect the short starter causes or increases this Larry.
If the patched ball is started and seated with a ram rod and no short starter or rod bouncing to seat it on the powder than shortening at loading will be minimized.
We find snow bullets substantially shorter than before firing with black powder cartridge lead bullets and these usually are a good bit harder being mixed with tin or antimony than lead balls for muzzle loaders.
A ball does not have near the mass up front for obturation to occur as does a bullet but as far as I can detect from pictures it seems to occur to some extent.

 

[Vaino]

Does your .54 have an even number of lands and grooves?...if it does, I'd be interested in the RB OD which would be the areas of the groove and the smaller areas which would be the areas of the lands. If you didn't save the balls, that's OK....but sure would be interesting to have this info...thanks....Fred

 

[Larry Pletcher]

Fred,
I'd look it over, but I just locked it up. It's a Rice .54 so I think it's a 7 land barrel. I think all Rice barrels are 7 lands and grooves. If I'm wrong somebody here will know.

Regards,
Pletch

 

[Vaino]

Just checked a Rice bbl...7 it is....Thanks....Fred