do heavy boolits obturate sooner

[targetshootr]

...than lighter boolits, speed and hardness being equal? ...since it takes more pressure to get a heavier bullet going. I have a NEI 340 gr 45 cal plain base mold and wonder what should be top speed using straight wheel weights and no g/c.

Also wonder if it will obturate more because it stays in the cyl and barrel longer.

[JeffinNZ]

I think it is more factory of sectional density IE: the longer they are in relation to there girth the more inertia will exist.

[454PB]

I've always wondered why people want obturation. Seems much better to cast a boolit large enough in diameter that it doesn't need obturation.

[targetshootr]

As I unnerstand it, it seals the bore once a boolit obturates. If it doesn't, gas gets around the boolit and creates leading which is why hard boolits need to be pushed faster.

[44man]

I do not believe in it at all. I fit the boolit to the throats and don't know if I get any at all being they are larger then bore size. I would rather size down the boolit as it enters the rifling instead of making it expand to fit. I shoot pretty hard boolits at all velocities from light plinking loads to hunting loads and they shoot great. I have also shot softer boolits very fast with no leading at all.
I do shoot slightly undersize boolits ( Throats only.) from my .44 SBH but I neck size so the boolit is kept straight in line with the throats and a hard boolit has given me several 1" groups at 100 yd's.
Undersize throats or boolits too small will never give the best accuracy no matter what gun you have, even a musket with Minie' balls. The more you reduce the obturation, the better. The more you get away from the idea, the smaller the groups will get.
In my BPCR I fit boolits to the chamber, I use a .464" boolit for a .4593" bore.
I will never tell you to use a too small but soft boolit so it expands to fit. They just make noise! :Fire:

[targetshootr]

I never gave it a lot of thought either but I was reading Handloader and it made me wonder if a big boolit would obturate sooner just because it's heavier.

Brian Pearce on the 45-270-SAA:

"A plain base also allows obturation or upsetting to fill throats (especially important with oversized throats) and create a proper gas seal, as long as bullets are not cast too hard. The plain base also creates less pressure than a comparable bullet with a gas check."

[475/480]

It seems he is just repeating what has been said before.Makes me wonder if he EVER knows what he is talking about.Also if the throats are oversize .002"+ is a boolit really going to obturate that much ( .002") without severe leading.

Sean


Brian Pearce on the 45-270-SAA:

"A plain base also allows obturation or upsetting to fill throats (especially important with oversized throats) and create a proper gas seal, as long as bullets are not cast too hard. The plain base also creates less pressure than a comparable bullet with a gas check."[/QUOTE]

[montana_charlie]

I agree with 44man...
Fit the bullet to the bore when you buy the mould...not when the charge ignites.
CM

[45 2.1]

I agree with 44man...
Fit the bullet to the bore when you buy the mould...not when the charge ignites.
CM

Matter of a difference of opinion, but I would think fitting it to the chamber and throat for a handgun and chamber, throat and bore for a rifle works much better.

[targetshootr]

From what I gather, a bullet should obturate if it works properly so it's one more thing to consider along with everything else. Maybe not top of the list but in there somewhere.

[Harry O]

Everyone has their own opinion. This is mine.

Every time you apply pressure to a metal, you will get obturation. As I said before, there is elastic obturation (good) and plastic obturation (bad for a well fitted bullet, but it can help with an undersized bullet). You apply pressure to a bullet when you ignite the powder. I believe that as long as the peak pressure for two loads is the same, the obturation will be the same.

So, a downloaded heavy bullet will obturate the same as a heavier loaded light bullet (if they both have the same peak pressure). If the heavy bullet is loaded to a higher pressure than a lighter bullet (using the same amount of powder, for example), it will obturate more (the pressure would be more).

It is interesting to note that many of the people who disagree with the 1,422 x Bhn formula tell of their tricks to get the bullet to go faster than would be predicted by the formula. Their "tricks" ALWAYS seem to be something that REDUCES the peak pressure. This may be using a slower powder or putting a cardboard (or other material, such as a gascheck) protector under the bullet (to spread the load more equally). Or, it may be any number of other things. But, whatever it is, it always seems to be something to protect the base of a plain base bullet.

Veral Smith says that some obturation is needed regardless of the bullet fit (he is VERY strong on making the bullet fit proper for the gun, not obturate just for obturations sake) in order to seal the rifling grooves as the bullet passes down the bore. I don't know nearly as much as he does about lead bullets, but it makes sense to me.

[targetshootr]

Well put. That's kind of what I thought. Does that formula give the pressure at which obturation begins on a given boolit?

[454PB]

My Ruger Redhawk has .4315" throats and a .430" bore, and only .002" barrel cylinder gap. I size my boolits .4315". Once kicked in the butt, any obturation can only happen in length of the bullet. You can't compress lead any more than you can compress water or boolit lube.

Some have suggested that the lube grooves will compress, but if the bullet fits the bore or is slightly bigger, it can't compress the lube groove without compressing the lube as well.

Maybe what some call obturation is what I call "sizing within the bore".

[felix]

Obturation is shortening the boolit and making it wider, including expanding the chamber along with the brass. Sizing the boolit is compressing the sides of and lengthening the boolit. Both must occur for the "bestus" accuracy. ... felix

[44man]

Something will always happen with the boolit when slammed with pressure but if contained well, it will be minimal. In the chamber it will expand with the brass to the chamber walls. I don't think that is as serious a problem as getting a crooked start in the throats.
45 2.1 is correct in that fittin a cast boolit to the chamber when seated is even better but most heavy revolver boolits have to enter the throat some. Boolit design is a factor. I have the big Lyman .45 boolit that goes a long way into the throats. I suppose the front of the boolit could be the only part sized but it is so accurate I won't bother. Might be a future test though. This boolit has shot a bunch of groups at 50 yd's that are one ragged hole and it has done 1" at 75 yd's. That is no small feat with a Vaquero and the sights on the gun. I don't see how I could tell the difference changing the sizing.

[Bass Ackward]

But, whatever it is, it always seems to be something to protect the base of a plain base bullet.


Harry,

I was not aware that the 1422 formula was a PB predictor?

But even if it was, look at Elmer's well publicised and tested load of 22 grains of 2400 for his HP White tested 34,000 psi. He loaded ammo and sold that around the world. That pressure figure is out of a test barrel that has no obturation into a forcing cone that has to be sized back down to raise pressure, so I suspect pressure in a wheelgun was higher than that. :grin:

That's a PB, 10 BHN bullet. That formula says can't be done. If that formula is meant to be a generalization across many factory designs and calibers with poor fitting bullets or newer bores, then I say it's a good guide for starters or for someone that wants to shoot fast and cheap. But it ain't no law.

Bullet design is so much of a factor to strength. So is proper bullet fit. Those are my best tricks, but controlling the rate of how that peak pressure comes up still determines your ceiling based on the variables of your gun. After shooting several handguns though out my lifetime, the guns never reached maximum performance with PB lead until about 10-12 thousand rounds. At that point, you pretty well know what you have and what you need in the way of hardness. That's my experience.

[45 2.1]

Harry,

I was not aware that the 1422 formula was a PB predictor?

But even if it was, look at Elmer's well publicised and tested load of 22 grains of 2400 for his HP White tested 34,000 psi. He loaded ammo and sold that around the world. That pressure figure is out of a test barrel that has no obturation into a forcing cone that has to be sized back down to raise pressure, so I suspect pressure in a wheelgun was higher than that. :grin:

That's a PB, 10 BHN bullet. That formula says can't be done. If that formula is meant to be a generalization across many factory designs and calibers with poor fitting bullets or newer bores, then I say it's a good guide for starters or for someone that wants to shoot fast and cheap. But it ain't no law.

Bullet design is so much of a factor to strength. So is proper bullet fit. Those are my best tricks, but controlling the rate of how that peak pressure comes up still determines your ceiling based on the variables of your gun. After shooting several handguns though out my lifetime, the guns never reached maximum performance with PB lead until about 10-12 thousand rounds. At that point, you pretty well know what you have and what you need in the way of hardness. That's my experience.

Good write-up John. Exactly............. There is a lot more going on than what that little formula indicates.

[44man]

I have never found anything that works as stated, from twist rate charts to all the other junk. The guys are right, you have to play with stuff to see and not believe all that is printed.
Marlin wrote me back about the 1 in 38 twist on the .44 and it was worked out on paper----IT SUCKS! :( They determined on paper what RPM's it took to stabilize the .44 bullet. Might work at 3000 fps! :mrgreen:

[Harry O]

Well put. That's kind of what I thought. Does that formula give the pressure at which obturation begins on a given boolit?

No, that is not where it starts. It starts at anything above zero pressure. The 1,422 x Bhn formula is approximately where it changes from elastic obturation to plastic obturation.

I have seen pictures in some of my casting books (don't remember if it was Veral's or not) of tapered groove marks. This is where gas escaped along the rifling and melted off some of the metal, soldering it to the barrel. I also remember seeing in Veral's book of some soft lead bullets with a rifling ring at the front and rear. Between them, increasing the amount of powder increased the amount of permanent deflection (from the rear, working forward). When I was doing experiments of my own, I found that leading did not occur until the pressure was a LOT higher than where the accuracy went to heck. You cannot depend on leading of a well fitting bullet to warn you to back off. The pressure of just about any normal load on just about any cast bullet does bad things to it.

When you get very much above that formula, you have to resort to tricks. No problem if you know what they are, but I have seen many times a new caster asking about solutions to his problems and being put down because he did not know the "expert" casters tricks.

I have shot some of Elmer's loads and remember brushing out light leading. I also remember reading in one of his books ("Sixguns"?) that they gave very little leading. But leading there was. That may work for others, but it has never worked for me. So go ahead and blast away about how stupid I am.

[45 2.1]

I have shot some of Elmer's loads and remember brushing out light leading. I also remember reading in one of his books ("Sixguns"?) that they gave very little leading. But leading there was. That may work for others, but it has never worked for me. So go ahead and blast away about how stupid I am.

Harry-
Elmer complained about a lot of things. Most all of them had merit. Now, did you shoot Elmers original design boolit, with his specified components and alloy with it. If not, you don't get to bitch about it. Do you know what he used in his loads and his directions to load them? Todays supposedly Keith molds are a very far cry from the original.

[44man]

Harry, tapered groove marks are USUALLY the result of a boolit skidding before taking the rifling. That opens a gas escape slot. Mostly the result of a heavy, soft boolit and a fast powder.

[Harry O]

Harry, tapered groove marks are USUALLY the result of a boolit skidding before taking the rifling. That opens a gas escape slot. Mostly the result of a heavy, soft boolit and a fast powder.

Actually, the taper can go both ways. When the wider part is at the front, the cause is what you say, skidding. When the wider part is at the rear, it is because of gas cutting (too hard a bullet and too low a pressure). Both cause leading. I did both when I first started casting, but did not know what I was doing wrong until I saw pictures of both and an explanation. BTW, the pictures were is Scovill's Peacemaker book, not Veral's book.

I also took out Elmer's "Sixguns" book last night and reread the part about casting bullets. He says near the end of that chapter that even with guns that have perfect alignment, a correctly fitted bullet, and a smooth bore, there can be leading with "hot" loads, like with 2400 powder. He accepted that as part and parcel of shooting lead bullets with his loads. I have absolutely no doubt that he did what he said he did when it came to accuracy and power. However, I also don't doubt that he had many times more experience than me with cast bullet handloads. He probably knew more tricks than I ever heard of. I cannot get good accuracy with any leading. In fact, the accuracy of my loads goes bad even before I get any noticable leading, so I stay away from it.

[Bass Ackward]

I did both when I first started casting, but did not know what I was doing wrong until I saw pictures of both and an explanation. BTW, the pictures were is Scovill's Peacemaker book, not Veral's book.

I cannot get good accuracy with any leading. In fact, the accuracy of my loads goes bad even before I get any noticable leading, so I stay away from it.


Harry,

I don't know how to avoid leading if you want to see where the top is. Sometimes you can go on up assuming you aren't causing a pressure situation and get things to come back in or settle down. Don't misunderstand, I am not advocating leading, just that it isn't always a show stopper for me in a handgun. Especially with mid range loads. In fact, if your intent is long term use between cleaning, you may DO better with a light leading load.

I do not want to cloud up the issue of gas cutting. But most people assume it only happens before the initial seal takes place. This isn't true. In fact, I wouldn't rate initial gas cutting as the most common cause. But let's say your seal was quick and perfect, you can still get gas cutting. That's why it's is important to be able to learn what you are getting and why or how it's beginning first. Chicken or the egg.

Once galling takes place and the lead starts to build, that means the next round is no longer taking it out. Therefore, the next bullet must size down to pass this point. If pressure is too low to cause a re-obturation in the bore, you cut. Then the leading progresses on out as streak leading. But once it goes on out, then you go back to a good seal condition and accuracy can come back better than expected. That's why you hear so many heavy handgun shooters cry and complain when they have to clean their guns, mostly because it's built up enough on the face of the cylinder to start causing timing issues. They know what it will take to get back.

And why a common slogan for cast is to "just shoot it". If you can't stop the leading, ignore it if it isn't create a hazardous situation and sometimes the gun will clean up itself as it smooths what is causing the problem in the first place. Grandchildren are a God send for this. :grin: This can be preferable to causing more problems by improper cleaning all the time if you don't have the patience. Sometimes you get lucky with new guns. Sometimes, you don't. :grin:

[Harry O]

There seems to be a misconception about the 1,422 x Bhn “rule”. It seems like some people think it is like a light switch. Lower, it works great. Just a little bit higher, the bullet disintegrates. This is not at all how it works.

I did some experiments several years ago when I was looking at this. I cast up one type of bullet with two different Bhn numbers (from memory they were about Bhn 12 and Bhn 18). I sized and lubed them the same and matched the size to a specific rifle. Then I figured out the “transition” pressure and figured out some loads that were a little under to a lot over that pressure.

What I found was that under that pressure, there was little difference in accuracy, but the groups tended to tighten slightly the closer it got to that pressure (note that I did not fire any squib loads or loads that were greatly under that pressure so I did not have a problem with gas cutting). Slightly over that pressure, groups slowly started to open up. When I got to about 1/2 to 2/3 again more pressure than 1,422 x Bhn, the groups were between 2 and 3 times as large as their smallest groups. Beyond that, I started to get leading and I had trouble keeping the bullets on the paper.

Whenever I want a load that will work, I start with this formula. Yes, you can go over that, but you will have to resort to “tricks” to get both accuracy and velocity. How many times have you heard “every gun is a rule unto itself”. Such loads are “high strung”. If you are willing to experiment enough, you can sometimes find a higher pressure load that will work. But not always.

The rest of my life is a lot shorter than the life I have already lived. I am not going to waste the time I have left fighting this battle at the loading bench or here. I use cast bullets with moderate loads. If I want maximum loads, I use jacketed. I also won’t waste my time responding to people that are more interested in arguing than in exchanging information.

[sundog]

Harry, your post speaks volumes...

[felix]

Yeah, Harry, a bag full of tricks never hurts. My favoite trick is to use chasers during and after experimentation, on whenever the gun appears to be opening up groups beyond expectation. ... felix

[45 2.1]

For a better description of this supposed rule see this:
http://www.lasc.us/FryxellCBAlloyObturation.htm

[Wayne Smith]

"chaser" Felix, that would be single malt??

[Bass Ackward]

What I found was that under that pressure, there was little difference in accuracy, but the groups tended to tighten slightly the closer it got to that pressure (note that I did not fire any squib loads or loads that were greatly under that pressure so I did not have a problem with gas cutting). Slightly over that pressure, groups slowly started to open up. When I got to about 1/2 to 2/3 again more pressure than 1,422 x Bhn, the groups were between 2 and 3 times as large as their smallest groups. Beyond that, I started to get leading and I had trouble keeping the bullets on the paper.



Harry,

What you have described is what Mr Marshall used to describe as the best accuracy comes just before leading begins. I have run your experiment many times over. It is standard practice for every new caliber I get so I know what to expect. And I hope I ain't agrivating you. Either way, sooner or latter you will see the light even if you don't right now.

Not to be argumentative, just food for thought:

Using the same ACWW and bullet design, I can alter this balance point you describe by several hundred fps in the same gun. Bullets sized the same, etc. etc, etc.

Take my 35 Whelen and ACWW can be as low as 1600 fps or as high as 2100 fps using the exact same powder with a 250 grain bullet? Do you know what trick was changed? Lube. Yep. That's it. And if you want to try this yourself use some LLA on an ACWW bullet and then come up with it changing lubes. I guarantee you will see a MAJOR difference as you change lube regardless of caliber. Now if you harden your bullets, this differential becomes less and less.

But here is another trick, I designed the same bullet profile and just adjust the weight from 210 to 255 grains so bullet fit was the same across the board. I kept the same lube and ACWW mix from the first batch described above. If I lower my bullet weight and keep the same bullet dimensions, I can raise this balance point from 2100 fps with the 255 grain up to 2400 fps with the 210 grainer. Same RL15 powder but charge is varied of course. Failure pressure is 32,500 for the 255 and 34,000 for the 210. Want a little more velocity? Change to a pistol primer and you can go up another grain.

That's the only tricks and these are available to every cast bulletier.

Still not a believer? I can do this with a 30-06 where the extremes will be even larger. I can get up to 2600 fps with ACWW because the case is larger in relation to the bore and bullets are lighter. This is a 150 grain bullet. Why? Because pressures come up slower. See the pattern? Want faster? Try a 50 grain bullet out of a 223 @ 2850 holding 1/2". Same ACWW batch as the other bullets. SO .... obviously caliber, case capacity, bullet weight, bullet design, all factor into that issue besides powder speed, primer, bore condition AND .... bullet hardness.

But look that 22 caliber stuff up on that chart. Clearly I am blowing that chart all to hell with the 22 caliber where ACWW craps at about 40,000 to 44,000 psi using plain old 4831. Increase case capacity to a 22-250 and I can show you 3200 fps before accuracy craps. Slow powder yea. Of coarse. Who uses Bullseye in a 300 Win mag with jacketed bullets? Don't you adjust powder speed there as you go up in bullet weight and case capacity? Peek performance powders are different for a 300 Savage than a 30/378 WBY Mag right?

Why does this logic have to be any different with cast?

So you have a lot more to factor in to that equation now besides "individual gun specifics" and you can see that chart / formula ain't worth the paper it's written on unless you don't understand these principals. Too many variables, that have nothing to do with tricks, just common sense cast principals.

[Harry O]

Harry,

What you have described is what Mr Marshall used to describe as the best accuracy comes just before leading begins. I have run your experiment many times over. It is standard practice for every new caliber I get so I know what to expect. And I hope I ain't agrivating you. Either way, sooner or latter you will see the light even if you don't right now.



Actually, this is not what I found. And, it surprised me. I found that (with a correctly sized bullet for the rifle bore and good lube) accuracy starts going bad long before leading occurs. It starts going bad slowly, but still we are talking about worse. When it gets to leading, the bullets scatter instead of slowly getting worse, but still, the accuracy was getting worse before. The gap between peak accuracy and leading was actually quite large.

I have been reloading for over 45 years. I have only been casting for 17-18 years (I got a late start). I have probably made every mistake there is, and I am still making them, but I have learned a few things. One of them is that a beginner should use the 1,422 x Bhn formula until he learns the basics. If he wants to branch out afterward, go ahead. I think anyone who suggests that a beginner should go for max velocity with a plain base lead bullet right at the start is doing him no favors. Throwing in the variables of sizing, base protection, hardness, lube and any of the other tricks you use are not something that a beginner should throw into the mix along with all the other stuff he HAS to learn when he starts casting.

I have had a few medical problems that last few years that are not going away. I have realized that I don't have all the time in the world to chase unicorns anymore. Max velocity with a plain base lead bullet is one of them that I decided was not worth the effort. Have fun chasing unicorns, but the 1,422 x Bhn number is real, it does have consequences, and it matches EVERYTHING I was taught in engineering.

[Bass Ackward]

Harry,

Sorry about your health. My prescription is an off season spent casting those blues away. By spring we will pray that you are better and I assume you will know what to do with the slugs.

The chart is a good place to start. The beauty to cast is that we get to do what we want and aside from safety, live with the results. If your happy going by the chart, then by all means use it. I do believe that it is worth seeing the other side just to know what affects what.

You can also affect this point, by how much lube you use should you ever want to continue this testing. Get a good Lovern style bullet and simply cut back and watch what happens. You may be different, but when the groups start to open for me, the bullets HAVE lost balance because leading began. It's just the bullet and the check took enough out for me not to be obvious. Do you know how I know? I cheat and use a bore scope. :grin: This is what you are seeing on the target. PB lead will remove some itself before you notice it, but this is not close to what a check will do.