Obduration in MLs

[Larry Pletcher]

I figured to start this rather than hijack the other topic.

Obduration in MLs has been an interest to me for quite a while. This was much discussed on another mailing list long ago. The problem to me is that, in most cases it is difficult to prove. I'm going to start at what can be proved and move to what is more difficult.

I shoot a paper-patched long range bullet gun. The bullet slides down the barrel easily with just the weight of the ramrod. If this bullet is fired with a mild load, say 40 gr, the patch is burned. Loaded with a normal load, say 80-90 gr, there is no burning. Instead the paper is creased heavily or sliced in thin strips. This seems to be evidence that when the bullet leaves the muzzle, it is shorter and thicker than when it was loaded.

If we could recover a bullet with ZERO damage from impact we could measure it. However trying to prove what was caused by firing and what was caused by impact would be impossible.

Another way would be to look at rifling marks. The length of rifling marks would tell us how completely the bullet "bumps up". Again recovering an undamaged bullet is the problem. I'm told that oiled sawdust does pretty well, but any damage is probably not good enough.

Here is where photography comes in. I have wanted to photograph a paper patch bullet separating from the patch. I want to be close enough to see the length of the rifling marks. If this could be done, the length of the rifling marks show direct evidence of obduration and how far forward the obduration goes.

This can be done with the right equipment. Here is a photo demonstrating the ability:

(Photo credit- Harold Edgerton at MIT)The flash duration was 1/10,000,000 th of a second)

The projectile in the photo was traveling 2800 fps ”“ far faster than we need for a ML experiment. If we can stop a bullet or ball at 1000 ”“ 1500 fps and examine rifling marks, we might be successful.

If it sounds easy, it isn’t - but I’m not too far off. Here is a photo taken a few years ago with more primitive equipment.

In this pic the .40" ball is traveling about 1000 fps. It breaks an infrared beam at the moment it sheds its patch. This triggers a flash in a dark room. The shooter has to hit the beam in total darkness, and the camera had to be focused on the spot on the beam that the ball breaks. We spent more time than I'd like to tell about getting this shot.

Using this set up to prove obduration with a bullet would be an easier task than with a ball. With a bullet in my gun, there are no rifling marks when the bullet is loaded. Any rifling marks in a photo would prove the existance of obduration. The size of the powder charge would determine how far forward the rifling marks went.

If I set about to prove that obduration exists in a fired ball, I would first have to load a ball into the muzzle and pull it back out to see the amount of rifling marks left by the patch. To confirm obduration, we would need to see a longer rifling mark on the ball in the photo than on the ball just removed from the muzzle.

All this is to demonstrate that it is much easier to argue about obduration than to prove it. I'm confident that obduration occures in soft lead bullet guns. My gut says it takes place in round ball guns but certain conditions might be needed to be able to measure it. I'd want a large ball, very tight patch, almost no lube, and plenty of luck. The list of problems to be over come is long - not the least of which is stopping a 540 gr bullet at 1100fps inside the lab, er I mean my garage.

I realize this is long. You can probably see why I haven't started on this right away.

Regards,
Pletch

 

[Stumpkiller]

Neat.

I have a ball recovered from a deer taken with a frontal shot that shows the weave of the luned patch pressed into the lead. Aparantly the wax or grease of the lube is not compressable - urprised me to see it. The lands are apparant as flats on the ball, but it really isn't showing the rifling much. The 0.021" patch smooths out the sharp definitions.

Also, the ball went from 0.490" dia to 0.520". Not much flattenning at all (but it was from a time when lead was hard found for me and some wheel weights may have snuck into the mix).

 

[hanshi]

I've known a number of people who were "obdurate" but never an ML. I do know of a disagreement about whether or not prb "obturate". :rotf: Please forgive me, Pletch, but I couldn't resist. The devil in me, I guess.

 

[nkbj]

My Fremont needs a fiber shotgun wad under an almost loose patched ball to group. That ball has got to be getting shorter.

 

[David W.]

Yes, it is difficult to prove. A heavy powder charge would almost certainly be needed to remove any doubt.

Thanks for your post!

 

[Larry Pletcher]

I've known a number of people who were "obdurate" but never an ML. I do know of a disagreement about whether or not prb "obturate". :rotf: Please forgive me, Pletch, but I couldn't resist. The devil in me, I guess.

Awh, Heck, Hanshi,
I tried to copy the word from the earlier topic and messed up. I usually switch these words and actually tried to pay attention this time. I tried to edit the post and messed up there too.It ended up as a new post below yours. (This has not been a guud kebord da 4 me.) And, I can't change the title. I'm giving up now.
regards,
Pletch

 

[hanshi]

I know that, Pletch, but I just couldn't help myself. 50 lashes; one for each word in my post. :grin:

 

[nchawkeye]

Yes, it is difficult to prove. A heavy powder charge would almost certainly be needed to remove any doubt.

Thanks for your post!

I've often thought that this is why some guns start to group better with higher powder charges...

 

[Bill Hall]

I've always thought that one way to document obturation would be to fire a ball straight up, with a heavy charge, and let it land in a pond. Then paddle a boat to the splash, dive down and find that ball. Easy, right? :rotf:

I suppose the theory of obturation is like a black hole. We know they exist, everything works in models, but we can't see them. By process of elimination, obturation must exist. And if you put the theory of obturation to work for your benifit, it works.

I rely on it with one of my daughter's rifles. Worn out barrel, shallow rifling, won't shoot straight with goex ffg. But if we use swiss ffg, goex fffg, or 777 (all higher initial pressure than goex ffg), the rifle shoots dead on. I must attribute the difference to more obturation of the ball, as the ball must squish into the shallow rifling better with that inital hard push. Just can't see it happening.

When it comes down to it, most of what happens in a barrel (muzzleloader, or modern) is a whole bunch of theory. I do hope to see you succeed with your goal of proving the theory though. Good luck. Bill

 

[Vaino]

Thanks for sharing your thoughts on this intriguing subject. Here's some of my thoughts...right or wrong. A TIGHTLY patched RB after loading is no longer round but has a flat at the tangency of the ball and because of the tangental compression, the sectional density has slightly increased. Upon ignition and the increasing pressure to overcome inertia, the rear of the ball moves first and thereby compresses the ball to produce an even tighter PRB fit. Don't know if this compression can be measured in a PRB, but the tangental flat and patch weave imprint would orient front and back and possibly the length could be measured. Big loads would exaggerate any compression. We know that conicals compress and that's the reason that the TC Maxiball has intermitent smaller dias because they're easier to compress and will better obturate the conical w/ the bore. Of course, ball dia., patch thickness and a completely clean bbl for each shot would be requisite. Recovering a spent, unharmed RB is the big problem, but perhaps a 1000 yd range and a large water container would do the trick. Would take some doing, though....Fred

 

[ebiggs1]

Great idea for a topic. :thumbsup:
Thinking out loud a bit. How about shooting into a water tank? Don't know exactly how just thinking.
If you had a barrel like the one you are testing with but it had no breech plug, you could see exactly how loading effects the ball. :hmm:

 

[Vaino]

Good idea asre a plugless bbl...it would provide dimensions of the unfired PRB. I was thinking of using a bbl similar to a modern artillery breech...nearly the same results but using the same bbl for pre-fire dims and then the actual firing. Again, all is for nought if the "unharmed" RB is not recovered....Fred

 

[roundball]

We know and there seems to be film evidence of the bottom layers of shot pellets getting squashed by the weight of the shot charge about them at set-back time...and the outside edges of those bottom layers...more so than layers higher up...get flattened against the bore walls.
Stands to reason a PRB would as well...to what degree and with what powder charge are some of the sticky points

 

[fho]

It is not hard to do ,just make a sawdust box. The slug gunners do it to look at there bullets.

 

[nkbj]

The problem is of course trying to push a projectile hard enough to get it to expand in the barrel and then slow it down without it expanding a whole bunch more. This video shows such, using two one gallon jugs of water in front of two coffee cans made into a tube filled with shredder paper. The bullet is straight soft lead.The rifle is a TC New Englander sleeved to .458" bore. The camera person is my best friend that married me oh so many years ago.

Recovering the bullet let me see that I needed to stack more card wad under the bullet base.

 

[tg]

I believe there is considerable obduration, we use to shot with a sand pikle backstop and there were always lots of elongated cylindrical shaped remains of round balls in the sand,often curved not straight and often usually in groups of two or three for some reason

 

[Rifleman1776]

Great pic. Congrats for taking effort to do it. How far from the muzzle was that patch and ball?

 

[Rifleman1776]

shows the weave

Not unusual. A good way to judge if a ball/patch combo might be right for your gun without burning a lot of powder is to seat the ball with a big hunk of your patch than pull back out. The ball will (should) show the rifling and imprints of the patch fabric.

 

[Rifleman1776]

I've often thought that this is why

some guns start to group better

with higher powder charges...

That will usually be a faulty conclusion.
The reason "some guns start to group better" with heavier charges is that faster twists do better with light charges and slow twist barrels require the higher velocities gained from heavier charges to group well.
Now....let the 'h' start falling on me with experiences of exactly the opposite. The is the ml game, the only absolute is that there are no absolutes. :v

 

[hanshi]

Great video and much food for thought.