Killing time revels intersting fine about obturation

[PacMan]

I always beleived in obturation but never really knew why. I started out this morning loading some ACWW cast this morning with the ideal that i could get some kind of ideal of the cylinder to barrel alignment.Using .5 grains of 700X which lodged the bullets about 2 inches inthe barrel. After driving them back out i had deformed the slugs to the point that i had my doubts about the accuracy of my test.(heck i am not sure if i can tell anything this way or not) but any way i was using a non checked GC bullet.

What i did notice was that all six slugs had varing degrees of deformed/flatten shank bases. They went from as cast size to as much as .003 out of round with all of the shanks being out of square/not flat.

Next move was to load up 6 more heat treated none checked GC bullets and try them out. As i thought would be the case they stayed uniform in dia. and none out of square.

What suprized me was the amount of deforming to the softh bullets with such a small charge.

Now weather this would relate to the accuracy of shooting GC bullets without the check i have not a clue.

Sorry guys,I recently retired and have to much time on my hands.

Dwight

[Bass Ackward]

Good job. It isn't always about the scientific validity of a test because we know that all situations are different and this is EXACTLY why you can't apply mathematics to an ever changing science.

Ever wonder why GCs are more accurate?

Pressure is not just a function of powder charge. It is also a function of alignment, leade and cone angles, bore finish, lube, hardness, etc. So if you have any of these that are not perfect, pressure JUMPS. This jump is often well beyond what appears to be logical or what you see listed in a manual.

This is the biggest factor for recommending over hardness to new or new gun shooters.

Irregardless of what happens to the front of the bullet during transitions, the base is the part of the bullet that pays the price.

The answer for GCs is that they don't get eaten away by pressure as fast as a PB slug.

[PacMan]

Bass i agree with preasure being a combination of things as you listed. What really stired my intrest was the many post asking about accuracy of GC bullets without the GC.

I am just thinking out loud here so bare with me guys.

Asumming that the mold will cast a bullet that has a properly cast bottom driving band and a round and centered gc shank and cast to a hardness that will resist obutration be more accurate than a softer bullet that shank deforms upon firing?

Using this very limited test shows that the soft bullet shank after firing and before it exited the muzzle was no where near the quality of bullet that i or most anyone else would load if it were a plain base bullet.

Now if it actually does affect accuracy the next step would be to find what hardness bullet is needed to not deform the shank with the desired load.That may be a good trick.

Dwight

[Bass Ackward]

Now if it actually does affect accuracy the next step would be to find what hardness bullet is needed to not deform the shank with the desired load.That may be a good trick.

Dwight


Well, that is the trick isn't it?

The point being that you expect pressure to be one thing, but can you be sure? It says pressure should be _ X _ in a manual. But it only was in the gun tested.

Bullet weight / length is another factor huh? Lets say that a bullet is too short (as defined by time) to rotate the cylinder into alignment before the bearing area breaks seal with the face of the cylinder.

Is the deformation or out of round coming from pressure? Or from the momentum of the cylinder that actually distorts the shank of the slug?

Who knows? The only way to tell is to decrease the time it takes for rotation (speeding up the bullet) or going to a heavier slug that has more bearing length to perform the task in a set time.

[PacMan]

Yes i understand what you are saying.
The reason i think that it was preasure that caused the distortion are two fold.
1st is the fact i was using a 200 grain bullet that will actually engage the lands before it leaves the mouth of the case.
2nd is that there was no flatting of the shank's side to indicate that it had struck the cylinder throats. The shank being smaller than the driving bands should miss the throats unless badly misalligned.I would think.

Which brings up another thought that keeps comming back.Unless the cylinder is in perfect allignment with the bore if you have to tight of fit bullet to cylinder throat the chances of the deforming that you relate to should be greater. I understand that ths play in most cylinders should make up for this but only if the play is equal on both sides.
In short the bullet needs some room to allign itself in most cases i would think.Come to think of it the longer the bullet is the more room it should need.

This is making my head hurt-ha

Just my thoughts.
Dwight

[Bass Ackward]

You are probably right. See any one of the variables listed above will also come with a corresponding increase in pressure.

Yet there are conditions that still allow for a good launch. For those individuals, the need for a check is minimized. The bearing length must successfully point and hold the nose of the slug into the wind as it exits the barrel.

If the bearing length / hardness is such that a uniform air flow pattern is established before enough of the slug exits, you get a good launch. If not, then that extra surface area and strength of the check could have made the difference.

If pressure exits uniformly around the slug, flight is not disturbed. And with a revolver, it must do this twice. Once at the cylinder face and at the muzzle. Two chances to ruin the base of the slug from gas cutting.

How far the accuracy from a successful launch would continue is a question for the design of the bullet and the purpose of the load.

Still, an insightful test.

[PacMan]

Well Bass the air flow business just went past my ability to deal with.
Anyway i think that we both agree that a GC bulet is the best way to get accuracy and a hard bullet builds on the GC's abilitys.

As often happens the discussion has drifted from one thought to others which is good as no good answer is without many thoughts.

I have enjoyed the conversation and hope that we both leave with some food for thought.

Dwight

[44man]

Very good test! Amazing how fast a boolit can be ruined, isn't it?
It is why I go overboard when I read about "low pressure" loads of Bullseye, 231 or Unique using soft lead.
Might as well put a line of boolits on a plate and smack them with a big hammer and make them all look the same.
It is the reason the gas checks were developed, lead too soft to take even that tiny bit of pressure. Imagine 7 gr of 231!
The gas check might save the base but what about the rest of the boolit?

[Bass Ackward]

It is why I go overboard when I read about "low pressure" loads of Bullseye, 231 or Unique using soft lead.


Ahhhhhhh .... yep, overboard is a good choice of word there. :bigsmyl2:


Sorry about the air description. But I find that focusing on one aspect of cast bullets often bogs people down and it may not be the problem that is causing them the most problem.

Everything, and I do mean everything, needs to be considered as a package that affects the launch. And generally, the more aerodynamic something is, the easier it is to launch well regardless of other events that may be happening to it. Hollow points and round noses are probably the fastest at establishing good air flow.

In essence, cast bullets can bury you in details and lose sight of the big picture if you aren't both knowledgeable in the particulars of the gun you are using and cast in general.

[9.3X62AL]

Threads like this one are what makes this place great. MANY THANKS, GENTLEMEN.

[targetshootr]

I may have misread this thread but isn't the whole idea to get the base of your boolit to deform in a good way?

And, iirc, Keith wrote that his pb boolits with a bhn of 10 or so were fine to 1200 fps.

[PacMan]

targetshooter-Well the thread ended up getting into a couple of different areas on bullet obturation but my orignal intent was to show how little pressure it took to distort the base on a gas ckeck bullet shank that did not have the GC in place.

Did you read all the post?

[targetshootr]

Yes I read it a couple of times and the jist of it seems to be that obturation is not a good thing.

[PacMan]

Well i would say that obturation is necessary if bullit fit is to small in order to fill the groves and seal off gas blow by.

But once again i was talking about a GC design bullet without the check applied. As i mentioned in the first post and in another reply to Bass was that their are a lot of question about shooting GC bullets without the GC.Some had better luck than others.

My thoughts was maybe a harder bullet would do better because i would not think that you would want any obturation of the GC shank for the reasons i mentioned in my origonal post. The shank on these 6 bullets deformed in ways that could not help but hurt accuracy.

[targetshootr]

In that case I misread it. I thought your experiment was to see the effects on cast boolits in general. And then things got into how incredibly hard cast boolits need to be and I find myself on the Keith end of the spectrum.

[PacMan]

No one said that the bullets had to be hard!!!!!!!!!!!!!!!!!!!!!!

[Bret4207]

IMO obturation is NOT what we want. Why do we go to the trouble of casting a perfect boolit, sizing it just so, carefully loading in brass opened with an M-die and seating it so that the diameter isn't reduced if we're just going to mangle it into putty when we drop the hammer? I believe we should be striving for minimum obturation. BUT- I also believe we get obturation to one extent or another no matter what. The test in this thread is probably statistically meaningless, but it does show things happen inconsistently. Reducing variables (the ones a noted author of cast bullet handbooks says don't matter or even exist) is our goal. BHN alone won't solve that no matter what. It's all about fit, balance and consistency.

[44man]

You fellas are mixing terms again! :bigsmyl2:
We NEED obturation---ALL the time. That means "to seal."
What you don't want is to make the boolit expand, deform or slump in order to obtain a seal, or obturate.
Even if a boolit holds shape but skids the rifling past the base band, you will lose the seal. This is where the check comes in, it will provide more "grip" at the base and hopefully stop the skid.
Slamming a too soft boolit with sudden pressure, even with a check, will still skid the base and lead the bore so in that case a check is a worthless expense because you will have defeated it's purpose.
Everything must work together, pressure peak, time and place of pressure peak, boolit hardness, GC or PB and boolit fit to the gun.
Even the nose shape of the boolit will aid or detract from your results.
Every test I have made for over 50 years has shown me that the faster the powder, the better the boolit must fit the gun and the harder it has to be to resist damage.
A slow powder that peaks when the boolit is fully engraved and is well down the bore, gaining speed, is the better choice. This is why it is silly to use a good dose of Unique for a fast boolit instead of H110 or 296.
Even 2400 can be considered on the faster side so a softer boolit is not as good as what you can get away with using 296.
Revolver cases are too small for anything slower then 296 because it can fail to burn fully, reduce velocity and in most cases, accuracy.
As you shorten your barrels, you also bring in many problems with powder choice.
I can't make your 2" barrel shoot like a 7-1/2" barrel unless I get near 30 BHN because a fast powder is needed. Sure, you can use 296 or H110 but you are just making fireballs in front of the muzzle.
I used to marvel at those shooting a .38 special with pure, swaged boolits and Bullseye where more lead was squirted from the gap then went down the bore. Then many thought a hollow base would be better!!!! It might make the putty ball "obturate."
Start to think in terms of "mechanical" instead of black magic. The gun is a machine and I don't see anyone using aluminum crankshafts in their cars or Alox in the oil pan.

[1Shirt]

Great thread. Always appreciate the 44Man comments, as they always seem to be well thought out on a common sense basis.
1Shirt!:coffeecom

[felix]

It might be easier for some folks to think of a piston in a car cylinder. Ping? Yep, the wrong powder. Or, the wrong ignition timing. Did you forget the piston rings and/or how they seal? You know, the rings are nothing but gas checks. ... felix

[Frank]

44man:
I used to marvel at those shooting a .38 special with pure, swaged boolits and Bullseye where more lead was squirted from the gap then went down the bore. Then many thought a hollow base would be better!!!! It might make the putty ball "obturate."
They win matches with those soft bullets so something must be working right. Maybe it's the low pressure round. The boolit needs to be soft enough to obturate. Now what's harder? Having to make bullets exact to fit a gun's dimensions, or just make a bullet soft enough that it conforms to the gun every time. But limit it's pressure so it doesn't skid. Or better yet, give it a HB so when you boost it's pressure, it expands to conform. :popcorn:

[44man]

44man:
They win matches with those soft bullets so something must be working right. Maybe it's the low pressure round. The boolit needs to be soft enough to obturate. Now what's harder? Having to make bullets exact to fit a gun's dimensions, or just make a bullet soft enough that it conforms to the gun every time. But limit it's pressure so it doesn't skid. Or better yet, give it a HB so when you boost it's pressure, it expands to conform. :popcorn:
Never has making a boolit change to fit has worked. There is no such thing as a "low pressure" load. Fast powder, but low overall pressures punch a boolit too fast.
The only way to shoot soft is with black powder.
Those matches are shot at close range anyway but you can't realize the amount of leading in the guns. I had to clean the guns for those guys and it took days to get one bore clean only to have a few shots fill it again. Ever see a smooth bore .38? Need a Roto Rooter in the barrel!
I cleaned many guns for the Cleveland police force, now where do you think I got all the lead for my muzzle loaders? [smilie=l:
Have you ever seen a revolver with lead packed on the front of the cylinder and frame?

[Frank]

44man:
I had to clean the guns for those guys and it took days to get one bore clean only to have a few shots fill it again. Ever see a smooth bore .38? Need a Roto Rooter in the barrel!

What's was their problem? Maybe they were shooting copper and didn't clean it, then fired a bunch of soft bullets and it built up.

[44man]

44man:
What's was their problem? Maybe they were shooting copper and didn't clean it, then fired a bunch of soft bullets and it built up.
No, 100% soft lead with fast powder. All Bullseye loads.
Not a single person was casting with WW boolits or water dropping. They all bought dead soft boolits. Not many of the police cast or loaded. They bought factory loads or factory swaged boolits. Issue loads were junk.
They would do a job on a BG, if you could hit them.

[Bret4207]

You fellas are mixing terms again! :bigsmyl2:
We NEED obturation---ALL the time. That means "to seal."
What you don't want is to make the boolit expand, deform or slump in order to obtain a seal, or obturate.


No, we're all mixing terms I'm afraid. I understand what you mean, and you're correct in the sense you mean, but in the sense we're using the word (which the engineers among us tell me is the wrong term, but I always forget the correct one) to "obturate" is to cause the boolit to swell or rivet as the pressure curve rises which mashes the boolit into the throat area and leaves it at throat size as it starts it's journey into the leade or forcing cone, allegedly ensuring the boolit will be of adequate diameter to obtain a grip on the rifling and seal the bore. What we should be after is a properly fitted boolit in the first place, one that is already large enough to seal the throat/bore. The only time we should desire obturation in the sense we use the term is in a poorly built gun that doesn't allow us to start with a boolit of large enough diameter, one that doesn't allow us to properly fit (seal the throat/bore) to start with.

In a properly made gun for cast the throat should be a fraction larger than bore proper which would allow us to chamber a boolit "fat" enough to seal without obturating.

Trying to redefine a term in common usage leads us to the same problem we have when we say "hard alloy". To one person it 16 Bhn, to another 35 Bhn. People are pretty much on board with the idea of using "obturate" to mean the riveting/swelling. Lets not add more confusion.

[Frank]

So what if the soft bullet spits a little lead out of the gap? You wanna see a gunked up revolver, go take a look at my BFR. It's got Felix lube all over the cyliinder. It's naturally lubed so it will never wear out. :lol:

[Bass Ackward]

The day is coming when good quality WW will be a thing of the past. Since the last high priced spike, everything got mixed in when it came back. So future wheel weight that enter the system probably will be contaminated. So people are going to end up using different sources of metal that may not HT. Either that or they will have to buy it which is seldom economical. Lino to mix is becoming scarce too.

So people are going to have to learning to live with obturation the choice to use it or not is going to become mute. Lower amounts of antimony are going to render many molds under diameter as well. This is going to trend folks to either less shooting, or smaller, cheaper caliber guns. By then expect jacketed to be even higher priced than today. Read an article about 12 things that were going to cost more this year and ammunition was one of them.

There are big changes ahead, maybe not for some of us, but life is going to change for the boomers and newbies. Learning a little now will make the transition easier.

[44man]

I agree with Bret and Bass. Terms are misused and become too common and WW metal will be a thing of the past. We might have to buy metals and mix our own but the tree hugger's might outlaw all lead in any form. Some stupid bird ate some lead and died--I would feel better if I had just shot the bird. The importance of a bird is worth a million humans.
Can't drill for oil or gas, can't take coal from the ground, can't build nuclear plants, can't put windmills up, can't put up solar power plants in the desert. NOT IN MY BACKYARD! Some worm might be harmed.
I have enough stink bugs here to generate much electric if you burn them. :bigsmyl2:
Even your vote has lost value. I feel so sorry for the next generation.

[kelbro]

I think more people need to experiment with soft lead and make up their own minds. I read it so often and just followed the notion that you can't shoot soft lead. Then I tried it, just because I had so much of it. I was really surprised how well it shot and did not lead the bores of my pistols.

[44man]

I think more people need to experiment with soft lead and make up their own minds. I read it so often and just followed the notion that you can't shoot soft lead. Then I tried it, just because I had so much of it. I was really surprised how well it shot and did not lead the bores of my pistols.
Done that, been there. 56 to 59 years of playing with revolvers has moved me away from soft lead. FAR AWAY! Only BP gets pure lead from me. The time, work and expense of getting soft lead to shoot right is longer then I have to live. Not worth the effort.

[kelbro]

Didn't take long :). These are 25yd target loads. Very accurate. Definitely not long range hunting loads but still a fun way to use up some of those buckets of tape-ons.

[44man]

Pure lead shot at the right velocity and push is most likely the best ever for hunting. I killed hundreds of deer with round balls and even the cap and ball. For larger animals, just make the ball larger.
The Maxi Ball from a muzzle loader is a sure killer.
The problem is that modern guns and powders do not work as well with it. For every person that can shoot soft lead, there are a million that can't do it. Even those that say it works will spend more time cleaning out lead then shooting.
I shoot for years without cleaning a barrel and never find enough lead to worry about, a few flakes on the first patch or none at all.
I have never, ever found any leading in a BP muzzle loader using pure lead. Just don't ask me to shoot it from my revolvers! :bigsmyl2:

[Jim]

Pure lead shot at the right velocity and push is most likely the best ever for hunting. I killed hundreds of deer with round balls and even the cap and ball. For larger animals, just make the ball larger.

Years ago, a friend killed a fairly good size doe with a .54 GPR. It was a head on shot and he hit her dead center in the brisket. He said she went down like a bag of sand. When he got to her, he found that the ball had exited the butt!

[44man]

Years ago, a friend killed a fairly good size doe with a .54 GPR. It was a head on shot and he hit her dead center in the brisket. He said she went down like a bag of sand. When he got to her, he found that the ball had exited the butt!
That is the very best factory muzzle loader made. I will never understand the in lines and sabot's. They work but are a pain to load the second shot.
I just love the round ball. The only reason I don't use them as much is that a revolver is more challenging. I sold my deer rifles but will never sell my muzzle loaders or revolvers.
A revolver is much harder to make effective on deer then the round ball. My learning with the revolver will never end.

[Jim]

I have that same model in a left hand caplock. Off the bench, I can hit a 3 lb. coffee can all day at a hundred yards.

[RobS]

and the distributor is the timing of the ignition of an engine just the same as the primer selection and powder selection of a reload allows for a cast boolit, whether it be of a softer or of a harder BHN, to launch smoothly or..............in some scenarios to not launch smoothly due to not fitting together or understanding all the pieces of the working machine.

[Frank]

kelbro:
I think more people need to experiment with soft lead and make up their own minds. I read it so often and just followed the notion that you can't shoot soft lead. Then I tried it, just because I had so much of it. I was really surprised how well it shot and did not lead the bores of my pistols.
I agree with kelbro. In some low-pressure calibers a dead soft bullet can shoot tiny groups at 50 yds. How does it do that? Things must have got better I guess. [smilie=1:

[Bret4207]

Balance. Find the right load with a design the gun likes and you can get any alloy to shoot, or so it seems. Weaker alloys may benefit from slower pressure curves, but then there are exceptions that make me question that. I think we get stuck with an idea and stick with it sometimes instead of trying something new.

[btroj]

Yes Bret, we do sometimes get stuck in a rut. In my opinion the only rule inshooting cast is that there are no rules.
We need to experiment more. Keep learning. What may have been in the past may not be now.
We also need to realize that we all have different requirements and needs from our guns. Not everyone is looking for the same thing.

I use some soft bullets, some hard bullets. In reality, I have no idea how hard or soft they are. Don't care, they all seem to work. That is my criteria.

Brad

[44man]

Yes Bret, we do sometimes get stuck in a rut. In my opinion the only rule inshooting cast is that there are no rules.
We need to experiment more. Keep learning. What may have been in the past may not be now.
We also need to realize that we all have different requirements and needs from our guns. Not everyone is looking for the same thing.

I use some soft bullets, some hard bullets. In reality, I have no idea how hard or soft they are. Don't care, they all seem to work. That is my criteria.

Brad
That is the way it is. Change things when you have a problem ONLY.