Testing round ball obturation theory. An invitation.

[Stormrider51]

All my life I have heard and believed that a PRB made of dead-soft pure lead will obturate or "bump up" on firing to better fill the bore and help prevent gas blow-by.  And yet when I mentioned this on another forum a couple of "experts" loudly claimed that obturation doesn't happen.  One stated specifically that he had never seen any evidence to show that obturation happens and that since the portion of the projectile facing the pressure is rounded instead of flat like a modern bullet the ball can't be shortened by the pressure.  Well, this left me with two thoughts.  One is that I need to prove or disprove obturation by direct testing.  The other was that I didn't want to be a part of any forum where a few members were allowed to dominate discussions and, even worse, be rude in their replies.  (I witnessed several newcomers being treated in an insulting manner.)  

I have a fairly well-equipped gunsmith shop and a number of years of experience in the shooting sports.  I decided to do some testing.  I took a short piece of rifled .50 cal barrel that has been laying around waiting to someday become a pistol.  It was perfect for my intended use as it had never been tapped for a breech plug.  I turned a brass cleaning jag down to a diameter that just would slip into the bore.  The face of the jag was a very close match to the shape of the ball and came up nicely around the sides.  I found a bag full of .490 balls sitting on a shelf and gathered up several thicknesses of patch material.  Let me note that the balls were cast of dead-soft lead.  I measured each one with micrometer calipers before use.  I also used a lube made of 50/50 beeswax/vasoline that I've used for years.  I decided to start with a patch thickness that would create what I consider to be a  "normal" fairly tight patch/ball combo.  By "normal" I mean that the PRB could be pushed through the bore smoothly using firm pressure.  The section of barrel was clamped in a vise.  Here's what I found.

Ball #1 measured .489".  I short-started it, cut the patch at the muzzle, and pushed it through the bore.  After peeling away the patch there were clearly visible impressions from the patch material around the circumference but no sign of rifling marks.  Interestingly, the  ball now measured .490".  Had obturation already begun just from the smack I gave the short-starter and being pushed through the bore?

Ball #2 measured .490".  I did everything as above except that this time I stopped short of pushing the ball all the way through.  Instead, I switched ends with the ramrod and pushed it back out again.  The result was almost identical to my first try.  The ball showed impressions of the patch and now measured a hair over .491".

Ball #3 measured .490".  Again, I did everything the same including stopping short of pushing the ball all the way through.  But this time I wanted to simulate the pressure of the expanding powder gasses on the rounded base of the ball.  I set the ramrod with its jag against the base of the ball and smacked it firmly with a leather mallet while pushing it back toward the muzzle.  The result was that not only were there impressions of the patch material, there were also clear marks left by the rifling.  More importantly, the ball now measured .492".

I intend to repeat these limited tests at least three more times to confirm my initial findings.  Then I plan to repeat them using a thinner patch and a thicker one as well.  The indication so far seems to indicate that a ball does "bump up" but this is where the invitation part comes in.  I'd like to invite anyone who has the ability to do so to repeat these tests and report their findings in this thread.  By compiling our data we can hopefully put to rest the debate over obturation.

The obvious best proof one way or the other would be to actually fire a PRB and recover it undamaged.  The "undamaged" part is the kicker.  Anything I can think of to fire it into will deform the front of the ball and negate the data.  Someone suggested firing it into a snow bank but those are few and far between in Central Texas!  If any of you folks "Up North" have access to a snow bank and the patience to try to dig a fired ball out of it....

Thanks,
John

[Riley/MN]

HA, Pitchy might have some from that snowbank he shoots inta (if it has thawed yet)

The other thing you could try... on a still day, shoot the ball straight up in the air and then just catch it when it comes down.....

Seriously though, I cannot imagine a soft lead round ball not bumping up - but I guess I have never been challenged on that before.

I will be watching this thread.....

[Gordon H.Kemp]

Stormrider51 , I think I know the site of wich you speak , and yes , there are several self proclaimed "Experts" that assume they have all the answers to all questions . I like the tests that you tried , and believe it shows that those of us that accept soft lead obturates when normal ignition preasures are applied to overcome the friction of the rule that an object  at rest, tends to stay at rest Etc.  I think that if you repeat the same test proceedure with a thinner patch there will be a tad more obtuation  (tapping it with the mallet) than with the tighter patch because there will be less resistance  to the obtuation of the ball .  Its my opinion that the ball can only obtuate to the actual measurement of the bore , but that it WILL obtuate .
         But , whats our opinion compared to the many great and glorious "Poobahas" that seem to be accepted as the last word in all things muzzleloading .
          Keep us posted on any updates , and THANKS !

[Swamp]

The other was that I didn't want to be a part of any forum where a few members were allowed to dominate discussions and, even worse, be rude in their replies. (I witnessed several newcomers being treated in an insulting manner.)

Stormrider, you have stumbled on the right place to be! You will not get that kinda response here I assure you. So now you have seen how others run their places, so why don't you just stick around right here, and be a part of the best traditional muzzleloading organization there is, the TMA!

Welcome my friend!  

[Loyalist Dave]

First, let me point out that "obturation" does not mean a mere deformation of the bullet, but means "the process of a bullet or pellet, made of soft material and often with a concave base, flaring under the pressure of firing to seal the bore and engage the barrel's rifling." Your tests noted that the ball was deformed, but a .492 ball isn't sealing a .500 bore right?  

Second, the ball may not be "smacked" by the gasses as you suppose..., it is possible  hit by the top of the powder column (which is softer than lead), which compresses as the powder column deflagrates.  This then may overcome a portion of the inertia and friction of the patched round ball, to start the ball moving forward, before the full powder column ignites and becomes gas, pushing against the patched round ball.  OR..., it might fully deflagrate before the ball really begins moving..., thus making your premise valid.  It needs testing.  

Your test showed that using a short starter the ball is deformed several thousandths of an inch, but not all of us use short starters.  Some have coned barrels, some use patch and ball combinations that are started by their thumbs, and some like me simply force the ball with a push, not a smack.  I also stop when the ball is steated, and don't bounce the ramrod on top of the loaded ball as some folks like to do.  I know such an action deforms the ball, and I try to avoid it.

To actually test, you need to fire the projectile into ballistic gellatin, which is used to recover any type of bullet (even pure lead) for ballistic comparisons.  Once recovered the bullet may be measured to see if it actually obturated, or if it simply deformed, and how much it deformed.  

However, I think that since most of us have recovered fired patching material uncut by the rifling, when shooting on the range, that's pretty conclusive proof that the ball doesn't "obturate" for it should cut through the patching material if the ball was sealing the bore.

LD

[Stormrider51]

HA, Pitchy might have some from that snowbank he shoots inta (if it has thawed yet)

The other thing you could try... on a still day, shoot the ball straight up in the air and then just catch it when it comes down.....

Seriously though, I cannot imagine a soft lead round ball not bumping up - but I guess I have never been challenged on that before.

I will be watching this thread.....

Riley...Tell you what, you come and catch the ball as it comes down.  Your eyes are probably better than mine and I'll loan you my old catchers mit.  You do that and I'll give you a cold mug or two of homebrewed beer.  

John

[Stormrider51]

Stormrider51 , I think I know the site of wich you speak , and yes , there are several self proclaimed "Experts" that assume they have all the answers to all questions . I like the tests that you tried , and believe it shows that those of us that accept soft lead obturates when normal ignition preasures are applied to overcome the friction of the rule that an object  at rest, tends to stay at rest Etc.  I think that if you repeat the same test proceedure with a thinner patch there will be a tad more obtuation  (tapping it with the mallet) than with the tighter patch because there will be less resistance  to the obtuation of the ball .  Its my opinion that the ball can only obtuate to the actual measurement of the bore , but that it WILL obtuate .
         But , whats our opinion compared to the many great and glorious "Poobahas" that seem to be accepted as the last word in all things muzzleloading .
          Keep us posted on any updates , and THANKS !

Gordon,
Thanks for the encouragement.

John

[Stormrider51]

The other was that I didn't want to be a part of any forum where a few members were allowed to dominate discussions and, even worse, be rude in their replies. (I witnessed several newcomers being treated in an insulting manner.)

Stormrider, you have stumbled on the right place to be! You will not get that kinda response here I assure you. So now you have seen how others run their places, so why don't you just stick around right here, and be a part of the best traditional muzzleloading organization there is, the TMA!

Welcome my friend!  

Swamp,
I've been reading on here for a few days and haven't seen anyone "flame" anybody else yet.  There's no point in it and when done to newcomers is just plain sad.  One guy over there reminds me of a chihuahua, always looking for someone to bark at.

John

[Stormrider51]

First, let me point out that "obturation" does not mean a mere deformation of the bullet, but means "the process of a bullet or pellet, made of soft material and often with a concave base, flaring under the pressure of firing to seal the bore and engage the barrel's rifling." Your tests noted that the ball was deformed, but a .492 ball isn't sealing a .500 bore right?  

Second, the ball may not be "smacked" by the gasses as you suppose..., it is possible  hit by the top of the powder column (which is softer than lead), which compresses as the powder column deflagrates.  This then may overcome a portion of the inertia and friction of the patched round ball, to start the ball moving forward, before the full powder column ignites and becomes gas, pushing against the patched round ball.  OR..., it might fully deflagrate before the ball really begins moving..., thus making your premise valid.  It needs testing.  

Your test showed that using a short starter the ball is deformed several thousandths of an inch, but not all of us use short starters.  Some have coned barrels, some use patch and ball combinations that are started by their thumbs, and some like me simply force the ball with a push, not a smack.  I also stop when the ball is steated, and don't bounce the ramrod on top of the loaded ball as some folks like to do.  I know such an action deforms the ball, and I try to avoid it.

To actually test, you need to fire the projectile into ballistic gellatin, which is used to recover any type of bullet (even pure lead) for ballistic comparisons.  Once recovered the bullet may be measured to see if it actually obturated, or if it simply deformed, and how much it deformed.  

However, I think that since most of us have recovered fired patching material uncut by the rifling, when shooting on the range, that's pretty conclusive proof that the ball doesn't "obturate" for it should cut through the patching material if the ball was sealing the bore.

LD

Dave,
Very good points and yes, I was using the wrong term for what I'm talking about.  Using "upset", "shorten", or "deform" would have been more accurate as the ball itself never touches the rifling in a normal load.  My question was whether or not the ball grows larger in diameter thereby compressing the patch material and helping to seal the bore.  It is my opinion, and opinion is the lowest form of knowledge, that it can't help but do so given the softness of pure lead and the laws of physics.  I'm looking for ways to test the theory and hopefully others to repeat the tests for verification.  Interested?

As for ballistic gelatin, I've used it to test the expansion of hollowpoint pistol bullets in the past and on one occasion even fired a lead ball into it for a comparison.  The pure lead ball mushroomed beautifully which would prevent an accurate determination of how much deformation was due to which factor.

John

[sse]

Riley...Tell you what, you come and catch the ball as it comes down.

[Riley/MN]

Riley...Tell you what, you come and catch the ball as it comes down.  Your eyes are probably better than mine and I'll loan you my old catchers mit.  You do that and I'll give you a cold mug or two of homebrewed beer.  

John

Ummm, I think I have a meeting tonight...

[Loyalist Dave]

My question was whether or not the ball grows larger in diameter thereby compressing the patch material and helping to seal the bore.

I think that's already been demonstrated by you.  It would deform and thus "tighten" the fit in most loadings.  Even if you didn't use the short starter, the ball does get some sort of sharp smack when it's launched, right?  There would be some "squashing" of the ball as it moves forward, from the powder blast.  You might see how tough it is to load a .495 ball vs. the same patching material and a .498 ball (Lee makes a mold).  If it's tighter than you can really handle, with a .003 difference, I think you can conclude it does seal the bore better than a human can.

As for the gelatin, you don't need to fire a full load, and you may need to check the gelatin mixture.  We wouldn't need to test for ballistic performance, just recover the projectile, so a softer mix would work.  For example, if you fired a 20 grain load instead of 60 or higher, you might have less expansion, but after all if 20 grains expands the ball by x amount, then 40 should to more, and 60 even more.  

It's also possible that a 20 grain load will give you all the expansion you will ever get (lets not forget the rifled pistols of the period eh?), as perhaps after the first 20 grains go boom..., the ball is moving forward thus not giving enough inertia to cause further expansion..., and the remainder of the load of say a 60 grain load, merely adds velocity?  

We'd need soft gelatin, and some really good shots, and hit the gelatin at say 100 yards..., thus allowing the ball to decelerate some, so we could compare.  If the ball from a 20 grain load isn't deformed more than from a 40 or 60 grain load, you'd know it does seal, it works with a pistol load, and the remaineder of the load accelerates the ball.  

I have also heard of firing a projectile upward at an angle into a silk handkerchief..., which supposedly will get caught and ride along with the bullet, and allow you to recover it..., but this was supposedly with revolver rounds, so again use a light load.  


LD

[Two Steps]

What about water?  Large stock tank...swimming pool...my front yard after a rain
Al

[Gordon H.Kemp]

I"d like to add at this time , for those who may just starting their  journey into the addiction of muzzleloading  and the history that surround these weapons , that wether or not a soft lead spehre  obtuates  is not relative to enjoying this hobby . Its just another fascet of the hobby that some wish to pursue .
          So just ignore the discussions such as this subject and enjoy the hobby for what it is . If at some point in your journey a question you would like answered arises , please ask , and there will be folks that will have the answers on this site . We all started not knowing many things and had to learn as we progressed .  Your questions will be treated with respect , and answered in a cival manner.

[Stormrider51]

My question was whether or not the ball grows larger in diameter thereby compressing the patch material and helping to seal the bore.

I think that's already been demonstrated by you.  It would deform and thus "tighten" the fit in most loadings.  Even if you didn't use the short starter, the ball does get some sort of sharp smack when it's launched, right?  There would be some "squashing" of the ball as it moves forward, from the powder blast.  You might see how tough it is to load a .495 ball vs. the same patching material and a .498 ball (Lee makes a mold).  If it's tighter than you can really handle, with a .003 difference, I think you can conclude it does seal the bore better than a human can.

As for the gelatin, you don't need to fire a full load, and you may need to check the gelatin mixture.  We wouldn't need to test for ballistic performance, just recover the projectile, so a softer mix would work.  For example, if you fired a 20 grain load instead of 60 or higher, you might have less expansion, but after all if 20 grains expands the ball by x amount, then 40 should to more, and 60 even more.  

It's also possible that a 20 grain load will give you all the expansion you will ever get (lets not forget the rifled pistols of the period eh?), as perhaps after the first 20 grains go boom..., the ball is moving forward thus not giving enough inertia to cause further expansion..., and the remainder of the load of say a 60 grain load, merely adds velocity?  

We'd need soft gelatin, and some really good shots, and hit the gelatin at say 100 yards..., thus allowing the ball to decelerate some, so we could compare.  If the ball from a 20 grain load isn't deformed more than from a 40 or 60 grain load, you'd know it does seal, it works with a pistol load, and the remaineder of the load accelerates the ball.  

I have also heard of firing a projectile upward at an angle into a silk handkerchief..., which supposedly will get caught and ride along with the bullet, and allow you to recover it..., but this was supposedly with revolver rounds, so again use a light load.  


LD

Dave,
I like the way you think.  Thanks for the insight and suggestions.

John