I used to know this, honest !

[watkibe]

For a given bullet weight and powder charge, which will cause higher pressure, a cast boolit, or a jacketed bullet ?
Put another way, if I have good data for a jacketed bullet load, can I substitute a cast boolit of the same weight ?

[geargnasher]

Is this a trick question? :razz:

Gear

[leadman]

There are alot of variables that affect the load. Under "normal" circumstances the cast bullet will cause less pressure. But bearing surface and alloy will affect the pressure.
Also most jacketed bullet load data is much too "hot" for cast loads. It is hard to get a 150gr cast boolit to shoot 3,000 fps in a 30-06 for instance.

This is why both cast and jacketed load data is available.

[onondaga]

Between a cast boolit and a jacketed the same weight and the same charge in the same firearm the cast boolit will have lower pressure because cast alloys are softer and have less resistance in the bore.

Jacketed bullet data can generally be used for cast boolits but it is very helpful for accuracy and prevention of leading to stay with the lower pressure loading "starting load" area that cast boolits will more likely tolerate. Unfortunately some jacketed "Start loads" are already well beyond the ultimate compression strength of cast boolits, but the danger factor is gone.

There is a sensible answer for this. You are asking a basic beginner question and need to fill your head with basics to avoid a lot of problems and trial and error. The Lee 2nd Edition Modern Reloading explains very well the relation of alloy strength to practical loading with great logic. The New Lyman 4th Edition Cast Bullet Handbook is also great. I prefer the Lee book for alloy selection basics, but the Lyman has more loads just for cast boolits. That is why I have both!

Gary

[Bwana]

"Between a cast boolit and a jacketed the same weight and the same charge in the same firearm the cast boolit will have lower pressure because cast alloys are softer and have less resistance in the bore."
I might have to argue the point in the case of linotype cast boolits. They are extremely hard. Given that, with "regular" cast boolits, if the seating depth is the same it should be ok

[onesonek]

"I might have to argue the point in the case of linotype cast boolits. They are extremely hard."

Hard they are, but I rather doubt they are harder than the gilding metal jacket material. Then too, you have less bearing surface with a typical LG boolit. And I would think, the hardess lead alloy still has has a lower friction coefficient than jacket alloy's.

[oscarflytyer]

I actually recently read somewhere (wish I could recall where) that a lead bullet would/could have/cause higher pressure!

This goes against everything I had ever heard/been told. But the logic presented was thus:

a jacketed bullet is sized smaller than a cast lead bullet and only has to engage the lands. It does not have to fill and seal the grooves.

a cast bullet is normally sized larger than a jacketed bullet so that it will fill the grooves and seal the bore. this is done to stop leading.

this "oversize" cast bullet - compared to a smaller sized jacketed bullet - has more surface contact with the bore and thus creates more friction - and more pressure - all other things being equal.

[Junior1942]

It's simple: a lead bullet contains lube; a jacketed bullet doesn't.

[Wayne Smith]

I'm no physicist, in fact I never took the course, but I find it hard to believe that a lubricated lower ductile metal will create more friction than an unlubricated higher ductile metal under similar conditions.

[waksupi]

One of the most important things to learn when you start shooting cast, is to forget what you know about jacketed bullets, and do not try to make them the same animal.

[blackthorn]

"all other things being equal"

Therein lies the rub----all other things are NOT equal!!!

[Tatume]

I actually recently read somewhere (wish I could recall where) that a lead bullet would/could have/cause higher pressure!

There was an article in a recent gun magazine that made this claim. It specifically applied to revolvers only. They hypothesis was that the cast bullet will obturate upon leaving the constraints of the cylinder throat, filling the forcing cone in the barrel. It is then swaged to groove diameter in the barrel, resulting in increased pressure. The claim was supported by firing identical loads in a revolver and an unported barrel of the same length, and measuring greater speed from the revolver. The deduction was that greater speed must be the result of greater pressure.

[Char-Gar]

Wat... I would suggest you buy a good book on reloading and read cover to cover before you get within arms reach of a reloading press. Your level of knowledge does not rise to the level of basic and I don't want you or somebody else to get hurt.

I am not trying to be mean or cranky...just concerned for your safety.

[felix]

Obturation can be substantial and cause an excessive initial length of the pressure curve, most especially if the neck tolerance is too close. Both lead and copper projectiles obturate and its just a matter of degree for whatever reasons. Those reasons are the maintenance of shooting cast boolits specifically. So, the velocity answer is yes, no, and then maybe all three, each with a very minor variation of the load. ... felix

[GaryN]

"There was an article in a recent gun magazine that made this claim. It specifically applied to revolvers only. They hypothesis was that the cast bullet will obturate upon leaving the constraints of the cylinder throat, filling the forcing cone in the barrel. It is then swaged to groove diameter in the barrel, resulting in increased pressure. The claim was supported by firing identical loads in a revolver and an unported barrel of the same length, and measuring greater speed from the revolver. The deduction was that greater speed must be the result of greater pressure."


If I read that in a gun magazine I would no longer pay much attention to what the author had to say. There are too many variables when using two different guns to claim that. How about one?: The cast bullet seals off the barrel better and "captures" more of the energy from the powder charge. Or two: the cast bullet is lubed and has less friction so it goes faster.

[GaryN]

The preceding was two reasons why cast would shoot faster in the same gun. Add to that a different barrel with different throat dimensions, different chamber dimensions, different rifling and the myriad of other differences, it's like comparing apples with potatoes.

[cbrick]

In a revolver premature forcing cone wear can be caused by high velocity and too soft of a cast bullet alloy for the load in magnums. The bullet obturates in the barrel cylinder gap making it larger than groove diameter and then swaged down by the forcing cone.

Don't take this to mean that you need to shoot diamonds in a magnum revolver, doesn't mean that at all but if you’re shooting a soft alloy at max pressure/velocity in a 357 or 44 Mag as examples you could well be putting excess wear on your forcing cone.

Higher pressure? Maybe, as felix said the pressure time curve could be increased making the pressure higher earlier. How much higher? Dunno but unless your running on the ragged edge already I would be more concerned with shooting an alloy of 15-18 BHN as opposed to around 7-9 BHN.

Rick

[Bwana]

"I might have to argue the point in the case of linotype cast boolits. They are extremely hard."

Hard they are, but I rather doubt they are harder than the gilding metal jacket material. Then too, you have less bearing surface with a typical LG boolit. And I would think, the hardess lead alloy still has has a lower friction coefficient than jacket alloy's.

Yes, but, the jacket is just that, a jacket. The core of jacketed bullets are far more ductile than linotype bullets. And the linotype runs all the way through. I destroyed a Lyman 450 handle sizing linotype boolits, Part of the reason was because they cast about .003" larger than ww. But they were HARD.

[cbrick]

Lino is about 22 BHN.

Jacket metal is about 99 BHN. Wish I could remember where I read that, I think the NRA cast bullet book.

Yes, lino is HARD as cast bullets go but not nearly the hardness of a jacketed bullet.

Put a little case lube on a lino bullet and run it through your sizer and size it .001". Now put a little case lube on a jacketed bullet and just try to size it even .001".

Which do you think is harder?

Rick

[onondaga]

The Lee 2nd edition is on sale for $10.60 at Midway:

http://www.midwayusa.com/viewproduct/default.aspx?productnumber=484416

This is a hard cover edition also and a wonderful book with great information on casting, alloys and cast loads..

Gary

[watkibe]

Thanks for all the widely divergent responses. I also thank those who expressed concern about my safety, due to my virtually complete ignorance about casting bullets.
I suspected (sorta remembered) that a cast boolit can often be safely substituted in a recipe for a jacketed bullet if the bullets are the same weight.
Onandaga, I always respect the info in your posts, and I thank you for tracking down Modern Reloading, second edition 2. Thanks.
I not only have the second edition, but the first edition as well; I bought it when it was first published.
On occasion I ask a "dumb" question just to stimulate interesting responses, and maybe learn something along the way. This was not the case with the question that started this thread. I just wasn't able to trust my memory on that point, and my patience with looking through all my manuals and notes had gotten somewhat thin. Ummm, what to do ? "I know", I thought, "I'll ask the good folks on CastBoolits." As expected, I got several answers that answered my question. Quite unexpectedly, I was also called inexperienced, and ignorant.
After reloading and casting boolits for almost 30 years, the "inexperienced" charge is dismissed. As for stupid: I was in grammar school when my IQ was tested. The result was 160 on the Stanford-Binet test. (on this test, 70 to 130 is considered "normal").
So, to one and all, whatever your motivation, thank you for sharing.

[firefly1957]

You need to put in caliber when you ask such a question! One of the problems that cast boolits run into in bottle necked cartridges is when the base of bullet is below case neck the bullet can rivet causing high pressure. Also lead acts different at high speed then copper if you want to test this put a ingot of lead in a vise and go at it with a hack saw then try as thick a piece of copper as you can find. Even though lead is soft you will find it is harder to cut than copper it has to do with the properties of each material. Or you can try the same in a drill press with smaller pieces of lead and copper.

[onondaga]

cbrick pointed out in #19 that jacket material is about BHN99. Our cast bullet alloys get no where near that. Many in the casting community, including some members here believe The BHN to load pressure relationship theory presented in the Lee manuals is hogwash and that ultimate compressive strength of bullet alloys does not translate to an area of accuracy sweet spot in a cast bullet load as Lee projects.

I do believe Lee and have repeated his testing procedure numerous times when working up cast loads.

Physically getting that experience under my belt has been a help to me in understanding a relation of the jacketed bullet to the cast bullet regarding the pressure of loads and the window of crossover between cast and jacketed loading data.

Those chapters in the Lee book on alloy BHN and load pressure are the most difficult to study and learn if you don't do the experiment and take an opportunity to prove Lee right yourself. There are so many new casters and so many old casters that are only interested in published load data and results that ignore the theories and only want group size. They don't do themselves or their firearms justice by not really working up loads with alloy and fit.

Jacketed bullet data can be helpful to you if you understand its relation to your cast boolits in your alloy.

Gary

[Char-Gar]

When it comes to things that might blow up in your face, memory is always suspect. The older we become, the more suspect it is.

Experience only counts, if we learn and can recall what we learn. There are lots of folks who have done things wrong for a very long time. They seem to be unable to learn from their mistakes.

High IQ only counts, if it helps us get through life with success. There are lots of very bright folks who don't have enough common sense to come in out of the rain.

The above is just my musings on this very rainy day in deep South Texas. It is not intended to speak to any individual or issue. Just some random thought from a gabby old fellow.

[onondaga]

A lot of us with the high IQ sometimes forget that IQ is only a potential and that the ability to achieve is something altogether different. Yes, I tested higher than the level you mentioned even as an adult, but achievement level in my life has taken wide variation generally dependent upon my desire or need to accomplish and of course, in my life, personal health has been a large factor.

Gary

[Char-Gar]

Intelligence is just one of the tools we humans have in our bag of tool to live life. Like any tool, it only has value to the degree and how it is used. It only is important if it is used for a valid goal. Hitler was one smart dude!

The same is true of education and most every other tool in our bag. A successful life often has little to do with either intelligence or education. Both tool are to be used and not worn as a badge to impress others and set folks higher on the food chain.

Just saying....

[44MAG#1]

mmmmm

[cbrick]

When it comes to things that might blow up in your face, memory is always suspect. The older we become, the more suspect it is.

No kiddin, I have always been an advocate of good notes both with handloading and bullet casting. Any more every day older I get the more important these notes become and the more detailed I need them to be.

Rick