1422xBHN: relationship b/n hardness and velocity [Archive]

44man

01-16-2007, 10:07 AM

That is so true. I tried a few makes of commercial boolits and all were undersize and very hard. I never got any accuracy with any of them. Lots of leading too.
I don't believe in the bump up stuff at all as far as very undersize boolits go. I believe the boolit should fit the throat, then any base expansion is the ideal situation. With a real tight fit or even an overize boolit, very hard alloys can be shot without any expansion.
Although it is true an undersize, soft boolit will bump up, help prevent leading when the proper lube is used, although I have seen disasterous leading with them, but they can bump up off center, deform the noses, mangle the grease grooves closed too fast so you will run out of lube before the barrel length is transitioned ( How much lube can be lost at a cylinder gap when the boolit is crushed?) and they are never as accurate as a proper fitting boolit.
After over 50 years of messing with all kinds of boolits and guns from muzzle loaders up, I can't put any faith in bumping up a boolit. It doesn't even work with a Minie' ball. I still remember the .38 specials with soft, hollow base wadcutters that would get so packed with lead that I could not see any rifling. Even the outsides of guns would be packed with lead.
The boolit makers have the same mindset as the mold makers. Make everything to what barrel makers say a bore is, how many of you have a .457, 45-70 bore? Or a .429, .44 bore?
The good man at Rapine offers many boolit molds in different diameters, very smart! Most of us have to order a custom mold or make our own.

9.3X62AL

01-16-2007, 10:20 AM

44--

I largely agree with your statement, esp. the part about starting the boolit out at the correct diameter to begin with. I do believe that yield strength of an alloy is a factor in the sealing equation somehow, but don't choose to go there myself. I think the most dramatic improvement I made in terms of accuracy improvement and leading prevention was with the 9mm pistols, by using throat-matching boolits (.357"-.358") in the SIG-Sauers (first) and in a couple others since that time.

carpetman

01-16-2007, 12:33 PM

Nah Veral Smith didn't invent any Mathematical equation for bullets. His equations were all for tax laws.

Harry O

01-16-2007, 12:42 PM

Actually there are several writers (other than just Veral Smith) who believe in this fornula. It was controversial, so I decided to test it myself a while back. If anyone is interested, I can dig out the details, but basically, this is what I did.

I cast some bullets. Plain base Lyman 375167 (the formula was never intended for gascheck bullets). Then I heat treated half of them. That gave two distinct Bhn numbers to work with (from memory, Bhn 15 and Bhn 22). I figured out the pressure point for both hardnesses (using the 1,422 x Bhn equation) and then used my Powley computer to find out what load that would be. Then I loaded up three cartridges each from well below that point to above that point. I went to the range and tested both (again from memory, it was from about 26gr to 40gr of IMR4064).

The gun was allowed to cool between 3-shot groups. I took the gun home and thoroughly cleaned it between one Bhn and the other Bhn tests. Each test was approx 30 rounds each. In both cases accuracy took an abrupt turn for the worse when the pressure passed the 1,422 x Bhn line. Although that is not a large amount of tests, I was only verifying what people I respect had said. It was enough for that.

Some additional details. I took the softer bullet up considerably higher than the crossing point. Accuracy was bad and got worse, but there was no leading until considerably higher pressure than where the accuracy went bad. Another detail. The accuracy was virtually the same for all groups when below the crossing point.

One of the people who posts here is of the opinion that he has "proved" that the 1,422 x Bhn formula is wrong. He has a lot of data posted on it that was given to him by others (competition shooters). I do not have a computer program what will tell me black powder pressures (like the Powley does for IMR powders). However, I have shot BP for some time and have a number of books on it. From that, it appears to me that ALL of his data is on the hard side of the crossing point. As I have pointed out to him, you CANNOT tell what happens at the crossing point unless you load some cartridges above and below that point. You have to cross it to tell if there is any change. This was never answered -- just ignored.

Ricochet

01-16-2007, 12:52 PM

So we have some saying that this is a number for a pressure you must load to or beyond to achieve proper obturation of the boolit, and one saying (with experimental data) that accuracy deteriorates abruptly when passing this pressure. Interesting.

felix

01-16-2007, 01:22 PM

It appears the equation does not take into account the diameter of the boolit in relation to the throat. We need to have that parameter included somehow, someway into the formula, along with the diameter of the throat. So, we need two things added to the formula which already includes the BHN, such that the final formula for P = f (BHN,THROAT,DELTA). ... felix

cbrick

01-16-2007, 01:28 PM

Below is a "cut & paste" fron an article by Dave Scovill in Handloader # 165, September/October 1993 on this subject. The purpose of the formula is for a guideline for "MINIMUM" pressure not max pressure. It is a guide and not a hard set rule as other factors of alloy composition and bullet size/fit come into play also. I still think there was earlier mention of this formula but I didn't find it so perhaps I am wrong about that.

While the BHN for any given alloy
yields some relative measure of its
hardness, Veral Smith of LBT came up
with a conversion factor that makes it
possible to evaluate lead alloys in
terms of pressure in pounds per square
inch (psi). If you have an alloy that
measures 12.5 on the BHN scale,
simply multiply the BHN by 1,422. In
this instance, 12.5 x 1,422 = 17,775
psi, or the pressure that will cause this
particular alloy to become plastic, or
malleable.

Rick

felix

01-16-2007, 01:49 PM

We need a formula for dynamic pressure, not static alone. Pressure tends to follow the center of the moving mass, and this is exhibited by seeing at the backstop a hollow base which was made out of a flat base during accelleration of the boolit. ... felix

Harry O

01-16-2007, 02:59 PM

The statement that you need to get OVER this amount (1,422 x Bhn) in order to get adequate obturation is wrong. This number marks the change from the "elastic range" to the "plastic range" on a lead alloy stress vs strain diagram. See http://en.wikipedia.org/wiki/Stress-strain_curve for general discussion. Note that the stress-strain curve looks a little different for a lead alloy (the one shown in Wikipedia is for steel or similar material), but they act the same way. The most important point on the curve (for ALL engineering, not just bullet casters) is the point where it goes from elastic to plastic. That is the yield point of the material. Also note that the peak stress is needed to make this work, not the cup or lup or some other "average" pressure.

This is what the stress-strain curve means to bullet casters. When stressed within the elastic range, the bullet will return to its exact size and shape after the load is removed (such as when it leaves the muzzle). When it goes OVER this amount, it goes into the plastic range. That means that once stressed, the bullet will never return to its original size or shape. The bottom of the bullet will be deformed the worst, which is the worst you can have for accuracy. Veral Smith actually has pictures in his book of a soft bullet that was loaded with increasing amounts of peak pressure. You can see the deformation increasing from the rear towards the front as the pressure increases. Obviously, if you have a deformed base (over the yield point), you will not have very good accuracy.

As far as bullet size, the bullet must be larger than the groove diameter. It will not give consistent results with a bullet that is smaller than the groove diameter.

Idaho Sharpshooter

01-16-2007, 03:16 PM

carpetman,

looks as if you are not only wrong on the 1442 issue, but a horse's ass to boot.
I do not agree with Veral's tax dealings...but it has about as much to do with this forum and his expertise as what sort of personal issues you bring to the table.
Besides lack of manners, of course, we got that one! Perhaps we could trade you for starmetal.
Grow up, nobody here cares about you...or your asinine personal attacks on forum members.

regards,

Rich
DRSS

45 2.1

01-16-2007, 03:28 PM

The bottom of the bullet will be deformed the worst, which is the worst you can have for accuracy. Veral Smith actually has pictures in his book of a soft bullet that was loaded with increasing amounts of peak pressure. You can see the deformation increasing from the rear towards the front as the pressure increases. Obviously, if you have a deformed base (over the yield point), you will not have very good accuracy. This is not always true! If the boolit is large enough and fills all the available space, then it doesn't have anyplace to deform out of shape to. Accuracy can be far more decent than you believe in this case. I shoot PP boolits this way with pure lead as the boolit alloy (at about 25,000 C.U.P.) and get better accuracy than you could believe possible. The same can be done with filler if you do it right.

Harry O

01-16-2007, 04:06 PM

I have shot undersized, soft bullets that MUST deform to seal the bore (for example, more than 5,000 rounds of 41LC bullets -- but other ones, too, that were not as dramatic). Having a soft bullet that can deform to fill an oversized bore is often times more accurate than harder, but still undersized bullets. However, it is still second best.

The best accuracy is a slightly oversized bullet. And, it can deform even if it is slightly oversized. In fact, according to every stress equation I have ever used, it is an absolute must. Just because you cannot see a difference by eyeballing it, does not mean it does not deform. Back when I managed a quality control department, we had some measuring instruments that measured to the millionth (1,000dth of 1,000th of an inch -- anodizing) of an inch.

There are deformations whenever you exceed the yield strength. That is a physical law. And it can be measured. And, it is random. So, in this case, some bullets may give much better accuracy than expected -- but you cannot depend on it. It is better NOT to deform the base, if the dimensions of the gun allow that.

cbrick

01-16-2007, 04:36 PM

Here is an article by Ken Easterling on bullet strength relating to terminal ballistics (after internal ballistics, after external ballistics) and what the alloy is expected to do inside the target (game animal). Getting the bullet out the end of the barrel is only part of the role of alloy BHN. It was originally (and still is) published on leverguns.com (http://www.leverguns.com)and is reprinted at this URL with permision of Jim Taylor and leverguns.com. It is a bit technical but it is guaranteed to accomplish its goal of getting the bullet caster to think about alloy strength and BHN to accomplish his goals for his shooting situation.

http://www.lasc.us/TaylorBulletWeakEnough.htm

Rick

Pilgrim

01-16-2007, 04:39 PM

I've thrown my opinions on boolit design at this forum a number of times, and 45 2.1 basically hit it on the head, at least from my experience. In the first place, the 1422 X BHN is the threshold where permanent deformation will take place. Oftimes folks refer to this as obturation. It has been shown, by Scovill I believe, that bullet bases will slug up as pressure increases above this point. He did his experiments with a SAA .45 Colt with the barrel removed.

As far as our shooting is concerned, IN FIXED BREECH guns, if your boolit diameter is greater than the groove diameter, and the pressure peak occurs after the boolit is in the barrel, then the only deformation that can take place with that boolit is in the nose region where it is unsupported. A boolit that begins to obturate while still in the throat of the chamber requires fast (e.g. "pistol" or shotshell) powders so that the pressure peak occurs early. If this happens and the boolit is slightly undersized re: the throat, but is aligned properly (not out of alignment with the bore), and the chamber is concentric, then nothing happens as the boolit will swage back to groove & bore diameters with no boolit distortion re: out of balance. If the boolit is not straight with the bore, and is smaller in diameter than the throat, then the obturation and swaging will create an out of balance situation and accuracy will suffer.

If you have a "bore rider" or a boolit that just fits the groove diameter, things can change quickly. Without obturation, if the boolit is slightly smaller in diameter than the throat, the boolit will have a path for gas cutting as it transitions from chamber, through the throat and into the rifling. The gas cutting can and will foul up your accuracy since it is never uniform on the base of the boolit. If you are shooting a GC boolit, you may never notice the leading as the GC will scrape it away with every shot and thus no lead build up. Gas cutting will still have taken place, and accuracy will still suffer. If your boolit obturates or is large enough so no gas cutting occurs, then no bullet damage will take place and all is well, except for the boolit nose. In this case if the pressure is greater than 1422 X BHN, and the nose is "long" (like a bore rider usually is) then the nose will deform into the grooves and this deformation usually won't be uniform. Again, acccuracy will go down the tubes. If your bore rider is a few .001 greater than bore diameter, but less than groove diameter, sometimes the nose support is good enough so this doesn't happen. On the other hand, if the nose is short (doesn't have a bore riding portion) then any deformation that takes place seems to be uniform, OR it may take greater than 1422 X BHN to cause a short stubby nose to deform to any degree. Anyway, the 1422 X BHN is more applicable to revolters than it is to any fixed breech firearm. In a fixed breach firearm, the 1422 X BHN only matters if the boolit design has some part of it that is undersized, or has a portion of the boolit that is essentialy unsupported, or partially so. I tried to make sense out of the formula and use it to my advantage, until I realized it really only applies to revolvers or "long nosed" boolits, After that realization, I just made sure to use non-bore riding boolits in rifles, and then forgot about trying to use the 1422 X BHN relationship. In revolvers, I believe it can be critical. FWIW...Pilgrim

MT Gianni

01-16-2007, 05:09 PM

Pilgram, no axe to grind but do I understand that the unsupported nose has the same pressure as the bullet base? My training in liquids and gasses says that pressure is defined as a resistance to flow. I assumed that psi would be equal on the base and sidewalls of a bullet where they contact the bore but tha tthe nose would have a much lesser psi with only air in front of it. Again assumed nose slump was caused buy a mis-alignment or undersized whipping action as the pressure attempted to make as much contact with the barrell as possible? Gianni.

cbrick

01-16-2007, 05:13 PM

Very well said Pilgrim.:-D

As for discounting the minimum pressure in rifles I think it would depend to some degree on as cast diameter, throat dimensions of the firearm, alloy etc. but yes, I think you are correct. With bore riders I agree with the exception of a bore rider that actually fits the rifling diameter properly (that's been kinda rare in my experience) but in any event an un-supported bullet nose is not a good thing and of coarse gets progressively worse as pressure and velocity increase just as you described it.

Rick

cbrick

01-16-2007, 05:25 PM

MT Gianni, yes & no.

Conventional wisdom says that as pressure builds the bullet base starts to move first with the nose resisting movement, shortening the bullet (by how much depending on pressure, alloy & BHN), an un-supported nose under these conditions slumps to one side or the other.

Its off track of this thread but this "shortening" of the bullet is one of the things that lead Elmer to design his flat lube groove.

Rick

grumpy one

01-16-2007, 05:48 PM

You can get a conception of the stress level within the bullet by drawing what we old engineers like to call a "free body diagram" of the bullet during its journey down the barrel. There are three main forces to think about if we ignore the rotational aspect (considerable stress is generated by accelerating the bullet to make it rotate to suit the rifling). One force is accelerating the bullet, and two are resisting this acceleration. First, there is gas pressure on the base of the bullet, and it varies widely during the 20-24" journey. Second, there is frictional resistance generated by contact with the bore - and this is the smallest of the three forces. Third, there is inertia: the force to accelerate the bullet is the mass multiplied by the acceleration achieved. These three forces are in precise balance at any instant.

Bullet stress is predominantly caused by the inertia effect. You can visualise it by thinking about a deep pool of water. Pressure equals depth by density. Hence the inertia-induced stress is low towards the end of the bullet nose, and very high low on the bullet base, increasing linearly in between. Thus the first problem you get with too much acceleration of the bullet (ignoring the possibility of rotational problems if there is not enough bearing area on the sides of the rifling), is that the base collapses. The nose won't deform until the base is way past the gooey stage. Of course the bullet can still accelerate with a gooey base; the barrel contains it like a glass contains water. However a lot of goo will be left behind on the barrel interior; this piston has no piston rings (unless we fondly imagine that the gas check precisely fits the bore).

Pilgrim

01-16-2007, 07:11 PM

If you believe that lead is compressible, at least to a small extent, then yes, the pressure on the nose could be less than that of the base. However, I think the diffrence would be very little as the alloy, at least in a barrel, isn't going to compress very much, if any. It can't, as the boolit can't get any shorter since it's diameter is fixed (e.g. groove diameter). Since it can't get larger in diameter, it really can't get shorter while it's confined. Basically, the volume is going to be a constant. You can fool around with thoughts of compression or not, but the boolit is as big as it is and will stay that way all the way down the barrel and to the target, as long as it doesn't fly apart enroute.

If you consider that the boolit is not compressible, then the pressure on the nose is the same as that of the base and both are subject to F=MA as the acceleration force. The base ain't ever going to pass the nose in the barrel! The nose however, CAN deform into the grooves while the base is accelerating, and I suspect this is what happens with BHN less than needed for boolits that have the capability of deforming due to form. Another way of looking at it is the base is beginning to move while the nose is deforming in place from inertia. The energy (F=MA x time) has to go someplace and it can be acceleration or deformation. The forces needed to accelerate the base are also being used as the deforming force for the nose. If it can't deform due to shape and constraints, then the base, nose and all parts in between are going to accelerate the same. Anyway, that's my Norwegian Village Idiot view of internal ballistics re: boolits and barrels!! Pilgrim

grumpy one

01-16-2007, 07:17 PM

Pilgrim, the only thing that can accelerate the front of the bullet is the back of the bullet. That is, the tip only accelerates itself, while the base accelerates itself plus every part of the bullet in front of it. Just think of the bullet as a liquid and you'll get it. Pressure increases with depth below the surface, which is the bullet tip.

And taking two grabs at this to get hold of it doesn't make you any kind of idiot. Engineering students in their first two years tend to take up muttering in their sleep over this kind of stuff.

leftiye

01-16-2007, 07:26 PM

Yeah, especially if the bullet is a fluid from too much pressure

grumpy one

01-16-2007, 07:29 PM

Yeah, especially if the bullet is a fluid from too much pressure

Yes. Up to the point where it yields, the "pressure" is just internal stress in the bullet, which ranges from almost nothing at the tip to lots and lots at the base. Then if you plot a cut-off line where the stress reaches the yield point for that alloy, the rest of the bullet below that line, down to the base, is goo.

cbrick

01-16-2007, 09:45 PM

Pilgrim, sure, the bullet can and does get shorter given enough pressure. Your correct that the sides of the bullet are constrained by the bore but . . . the bullet has lube grooves and crimp grooves. If the bullet shortens no, it doesn't get larger in diameter than the bore but it can and does get shorter by filling in the lube and crimp grooves sqeezing out the lube. This is part of the lube process. Only bullets that are hard enough to resist the pressure applied could avoid this and its possible that could be too hard for the base to properly obturate.

Rick

waksupi

01-16-2007, 09:46 PM

Gentlemen, play nicely.

Harry O

01-16-2007, 09:51 PM

Lets talk a little bit about what "obturation" is or is not. Some people think that when the bullet is undersized, the pressure of the powder will shorten and increase the diameter of the bullet. If it increases the diameter enough to close the gap, that is good. Everything said so far is true -- up to a point.

Whenever pressure is applied to any lead alloy we use, it deforms. The bullet will get shorter and increase in diameter. The rate that it changes is a constant (for each type of material). Double the pressure and the deformation doubles. The rate is called "the modulus of elasticity" (see also "Poisson's ratio"). So a bullet can deform to fill a gap (if it is small enough), but it will spring back into shape after it leaves the barrel -- if and only if the pressure is below the yield point. Keep in mind that gap does NOT *only* mean diameter. There are also gaps caused by uneven widths of rifling. When there is a gap on the side of one of the lands, the gas will escape there first when the bullet reaches the muzzle. It will be deflected. Read Veral Smith's book for more on this.

If the pressure is above the yield point, the modulus of elasticity no longer applies. There is no constant between pressure and obturation. The length of time the stress is applied is now comes into play. The longer the stress is applied the more deformation will occur. What is worse is that if it has been stressed above the yield point, it will never return to its original size or shape.

The information given by grumpy is exactly what I believe happens with the bullet -- the intertia and the pressure working from the base, forward. Again, There are pictures of this exact thing happening in Veral Smith's book. My opinion of this book is that it is necessary by everyone who posts here. It is an "advanced degree" in how lead acts under pressure. Although Veral Smith is not an engineer, he is a shrewd observer, has done a LOT of tests, and is very logical in his conclusions. I do NOT have anywhere near the experience with bullet casting he has, but I worked for over 20 years as a structural engineer and I can see that everything he said is supported by what I was taught as an engineer.

grumpy one

01-16-2007, 10:19 PM

Gentlemen, play nicely.

I think I'm the only one that could be meant for, and if so, my apologies - I hadn't intended any insult to anyone. I'll stay out of it now.

grumpy one

01-17-2007, 12:14 AM

I now realize I was not the intended recipient of that counselling message - I must be hypersensitive or something.

Harry O, where the bullet has not yielded, the pressure it applies to the barrel interior is just based on elastic deformation of the bullet and is fairly moderate. In the lower part of the bullet, below the line where the bullet metal reaches yield stress, the part of the pressure that is not withstood by the metal has to be applied hyraulically to the barrel interior. In other words, you can calculate a total pressure at any point in the bullet by drawing a line from zero stress at the tip, up to full gas pressure at the base. You can then find the point where that line equals the yield stress of the bullet metal. Below that point, if you subtract the yield stress from the total pressure, the remainder has to be supported as a hydraulic pressure against the barrel interior. That remainder increases linearly from zero at the point where yield stress is just reached, to gas pressure less yield stress right at the bullet base. That gas pressure less yield stress is applied to the barrel interior via the lube. Seems like if that is too much pressure for the lube to withstand, it will burn up - and this will always happen first at the bullet base.

It is also worth bearing in mind that the part of the bullet that is below the yield line, being goo, cannot contribute to rotational acceleration of the bullet - so as the yield line moves up the bullet with increasing gas pressure, the risk of "stripping the thread" in the rifling increases.

cbrick

01-17-2007, 01:18 AM

I think I'm the only one that could be meant for, and if so, my apologies - I hadn't intended any insult to anyone. I'll stay out of it now.

I now realize I was not the intended recipient of that counselling message - I must be hypersensitive or something.

I couldn't figure out who that was meant for ???? I didn't see anything amiss.

Rick

ktw

01-17-2007, 01:20 AM

Thanks for the discussion.

Based on this thread, and some other reading I've done over the last 24 hours, I've come to the conclusion that for plain based boolits it would be a good idea to stay at or below the '1422 x BHN' pressure point for a given alloy. Obturation is not necessary in this particular application (plain based heavy cast in a 45 Colt carbine) as I have plenty of 'as cast' diameter to work with. I suspect you may be able to cross this alloy threshold to some degree when using a gas check.

There isn't a whole lot of published load data (with pressure) for 325+ gr cast loads in a 45 Colt. Found a couple load possibilities (based on Hodgdon, P Kelly, J. Linebaugh) that should work within my alloy constraints. I ordered a copy of Load From a Disk to assist with predicting loads that meet alloy pressure constraints in the future.

-ktw

MtGun44

01-17-2007, 01:45 AM

"It is also worth bearing in mind that the part of the bullet that is below the yield line, being goo, cannot contribute to rotational acceleration of the bullet - so as the yield line moves up the bullet with increasing gas pressure, the risk of "stripping the thread" in the rifling increases."

I would like to politely differ.

Just because the metal is subjected to a load higher than the proportional limit
(yield stress) it doesn't change state and is not "goo", it is just heavily loaded.
It will carry other loads just like under any other loading condition.

One key point is that properly fitted bullets will not need significant obturation
to fit the bore, and will retain their original shape more completely. A very
hard bullet that fits the throat and bore very well doesn't need obturation
to shoot well.

For some guns with undersized chambers which don't permit properly sized
bullets to chamber, obturation is mandatory for any accuracy. Otherwise
obturation may be harmful to accuracy in many or most cases if it occurs
beyond a small amount, as the bullet's change in shape is not necessarily
under control. Large amounts of uncontrolled bullet change in size will
not likely add to accuracy in most cases.

In revolvers, this shape changing as the bullet moves from
chamber to throat and then jumps the gap to the bore is fraught with
dangers of size (mis)matching and lack of or excessive obturation.

Knowing about what pressure will be required to obturate can be helpful
in designing a load (bullet slection, alloy, size, HT, powder speed, charge,
etc) to obtain desired results. This is the value of this formula. I doubt
that any hard generalizations about the effect of reaching the yield stress
are going to be particularly useful, it is just a piece of information to
use for load design, go past it if you want, avoid it if you need to, as your
conditions and intent require.

Another structural engineer. Been there done that for 30+ yrs.

Bill

45 2.1

01-17-2007, 07:54 AM

Some of the above discussions might relate to materials, but are not what is going on in a barrel at all times. Dr. Mann (of "The Bullets Flight") did a lot more on this than Veral thought of. The short or no barrel experiments are documented in Dr. Mann's book also. All boolits are permanently deformed on going into the throat and barrel by the rifling. Oversize boolits can lengthen. Undersize boolits can foreshorten. The point is to fit the boolit to the throat and use an alloy that matches the pressure level that your using. Not all of the boolit realizes the same pressure. Pressure reduces as you go farther away from the point it is applied. At the levels we normally use (those listed in the cast manuals), the boolit isn't goo either. What your seeing is the result of flame cutting from the powder burn. The lead alloy or PB is not exposed to the flame and pressure for long enough for that to happen. Go take a cutting torch and pass it over a boolit and see for yourself.

Taylor

01-17-2007, 08:06 AM

45 2.1

01-17-2007, 08:16 AM

Bass Ackward

01-17-2007, 08:38 AM

The equation is just a guide, nothing more as it only outlines what would be more ideal than just guessing. There are numerous ways to beat and cheat that equation. The complete answer is in bits and pieces, a line or two in one article and some more in another. I've never seen the idea related completely in any article i've read, past or present.

Great way of stating both posts!

Newtire

01-17-2007, 09:03 AM

While I have not done any scientific testing other than actually firing the boolits, I can say that I tend to side with the opinion that this formula only gives us the point that the alloy begins to distort/obturate. If the boolit is of good design to fit makes a big part of the difference whether it will work or not. I am shooting some boolits in my .30-30 that (according to this formula) should be over their limits and the Ranch Dog survives in my .444 with max loads of 4198. The M1 carbine boolit is another example. So anyway, I tend to think it would be only one factor in a big picture rather than the whole enchilada formula. I just go with what works. I agree with the playing nice bit too...

Slowpoke

01-17-2007, 11:49 AM

In a couple of recent threads there have been references to the working pressure of a boolit alloy in terms of '1422 x BHN'. Can someone either expound on this a bit, or provide me with a pointer to where it is discussed in more depth?

Specifically, does that represent the midpoint of a desirable range? The edge where bad things start to happen (or good things are just beginning)....

I've been planning out some more load development work (Lyman 457122-HP and Lee 457-340 in a 45 colt levergun). My initial round of casting was with a 12-13 BHN alloy and results were good out 1500 fps (i.e. reasonable accuracy, no leading)

I'd like to do some work in the future with some 8-9 BHN range scrap alloy and was wondering what to expect in terms of a target presssure/velocity range. When you calculate out '1422 x BHN' for 8.5 BHN alloy you don't appear to have much of a pressure range to work with.

-ktw

The best treatise on this that I have ever read is in the Cast Bullet # 131, Jan.- Feb. 1998, Titled Chamber Pressure and Brinnel Hardness By Steve Hurst

In the end he was satisfied with the relationship for a better Max pressure across the board for hard and soft lead would be BHN X 480 X 3 +10,500 psi .

He ended with "In actual practice, maximum pressure is a gray area rather than a strict limit because all the contributing factors are not known and those that are known are difficult to quantify."

good luck

Ricochet

01-17-2007, 11:57 AM

Pilgrim's explanation makes sense to me.

As for the pressure on different parts of the boolit, the air resistance in the bore is negligible. The gas pressure can be thought of as acting evenly across the base of the boolit, the boolit accelerating all together at a rate proportional to that force and the boolit's mass (neglecting bore friction, which is a smaller force), and at different cross sectional levels from the base to the nose of the boolit the force of acceleration acting over that cross sectional area should be proportional to the mass of the part of the boolit in front of that plane and the acceleration. If the boolit were a perfect cylinder, the pressure on the lead would steadily decline in a straight line from the peak gas pressure at the base to zero at the nose (neglecting those minor factors like bore friction and air pressure.) Wherever the pressure along the boolit reaches the thresholds already discussed for elastic and plastic deformation, the boolit will tend to shorten and bulge laterally, either temporarily or permanently. If that doesn't happen until that part of the boolit is already fully supported by the bore walls, it can't make a difference in the boolit's alignment. Now's where lubricants start entering into the picture. If the lateral pressure of the bulging boolit against the bore wall and the coefficient of friction of the boolit metal and the bore surface result in a longitudinal force at the surface sufficient to shear off a layer of metal, bore leading will result. If the lubricant has sufficient film strength under those conditions of dynamic loading to keep the metal surfaces from contacting one another, it won't.

Ricochet

01-17-2007, 12:01 PM

In the end he was satisfied with the relationship for a better Max pressure across the board for hard and soft lead would be BHN X 480 X 3 +10,500 psi .
Isn't that the same as saying (BHN X 1440) + 10,500 psi?

scrapcan

01-17-2007, 12:56 PM

It has been a while since I read through what I could find on this subject (was done for a special project for mechanics of materials). I think this equation from the article mentioned, BHN X 480 X 3 +10,500 psi, keep the terms seperated. The 1422 term is a simplified term and does not let you get back to the original terms in an equation. To most this is a small issue, but to engineers it is wise to keep all terms sperate so checks can be done to find errors when they occur.

This can be seen first hand when you read about the mars lander that smacked into the surface due to inconsistances in units. The error would not have been caught had terms not been carried through.

On the use of the curve for yield stress relationships. Another way to look at this is when punching holes in a metallic substance. You want to stay inside the yield limit so the hole is the size you want it to be, not over the yield limit where it is uncontrollable. I saw this first as a kid and did not understand what was happening until about 30 years later. A friend had punched holes in hardened steel for use on a chisel cultivator. He built a large press to shape and punch holes. He had a heck of a time experiementing until he came up with a punch that worked. Had he the experience ( or money to pay someone who did have the skills) to do the calculations it would have saved him
a year or 2 and many failed attempts. But hey experimenting is half the fun.

Punching holes in a forged horsehoe will show you this. Try to punch a hole with the metal to hot (effectively changing the curve) and you get holes not to your specs. Let the metal cool so you are in the range of plastic and you get nice holes that fit your nail. You do have distortion when the pritchel (punch) goes through, but it returns to the desired shape when load is removed. You set your nail head seat with the metal above the yeild limit so you get permanent distortion with the forepunch, two separate processess. Works the same with Aluminum. Lead is also included. But not all materials fit the curve theory, some composites do not.

Anyway just thought I would shed some light from another set of materials other than lead alone. Sometimes it helps to look at the world through a different window to understand the picture you are looking at.

Now it is in the rest of your hands to correct what I have said and help me learn if I am using things out of proper context or just flat wrong.

Ranch Dog

01-17-2007, 01:36 PM

Interesting topic! It's simple for me for cast boolits at rifle velocities...

1. A boolit that fits the barrel.
2. Rifle powders for rifle boolits that deliver at least 85% case density and not over 100%.
3. 1422 X BHN = PSI as a base line for investigating MOA perfomance during inital load development.

I shoot cast boolits in 12 out of my 15 Marlins. They all deliver sub-MOA performance at jacketed bullet velocities. I'm a simple guy, I don't need to understand all the in's and out's or rewrite the rules as long as I can reach out to 200-yards and dependable kill a big-game animal.

I enjoy reading all your thoughts!

Ricochet

01-17-2007, 01:52 PM

Harry O

01-17-2007, 02:07 PM

I read in Richard Lee's book that 1422XBHN is the max pressure that a cast boolit can stand.I called Lee Precision with this observation,and they did not have an answer for the difference.So now I am confused,who is right? I am real glad someone brought up this topic.Maybe I will get a better understanding,however Smith's equation does seem to make more sence(sp?).

I am not sure what you are reading. I have both books and both seem to be saying the same thing to me. If the peak pressure developed by the load is less than 1,422 x Bhn, you can expect good accuracy (assuming the plain base lead alloy bullet is reasonably well fitted to the barrel). If the peak pressure is MORE than 1,422 x Bhn, you cannot expect good accuracy. You may accidently get decent accuracy and, as mentioned before, there are many ways to "cheat" to move the limit upward, but you cannot routinely expect accuracy.

One of the ways to "cheat" the limit that I am aware of is putting something soft between the powder and the bullet. After the tests I ran, I later tried some with the softer bullet and plastic shot filler between the powder and the bullet. It moved the transition point between good accuracy and poor accuracy up about 10% when compared with no filler. I would expect that a couple of cardboard or fiber wads with a lube disc between them would do the same thing. For that matter, a gascheck will do even better. When using a plain base lead bullet, however, that dividing line has worked pretty well for me. And it has explained a number of failures that I had in the past.

Harry O

01-17-2007, 02:25 PM

Well, on that formula BHN X 480 X 3 + 10,500 PSI there are no units on the 480 and the 3. I have no idea where they came from. I don't see how it can be useful to keep 480 and 3 separate. We need more info about what those numbers mean. Applying a formula by rote without knowing what the factors refer to isn't that helpful IMO.

I have a suspicion that this may be a somewhat useful first approximation but there are going to be many complications applying it in practice.

Actually, the 1,422 is what can be traced back. I have seen 480 x 3 before, but have not seen how it traces back to anything (I have seen other numbers up to 1,450, too, but not where they came from). Brinnell hardness is measured in Kg per mm^2. The pressure developed by cartridges (at least in the US) is in Lbs per in^2.

1,422 is the conversion between the two.

1 Kg = 2.205 Lbs
1 inch = 25.4 mm

2.205 x 25.4 x 25.4 = 1,422

A Brinnell hardness tester pushes a ball into the plastic range of the material being tested. It is held there for 30 seconds. During that 30 seconds, the indentation spreads out (yes, I have done this with an industrial tester at 5, 10, 20 and 30 seconds to see the difference -- it does spread). It spreads out and deepens until it reduces the pressure down to the yield point of the material being tested. At that point, it does NOT spread any further. At that point, it stabilizes and all within 30 seconds. So you are essentially measuring the compressive yield point of the material with a Brinnell test. That is exactly where the bottom of the plastic range of the stress strain curve is.

It is NOT a perfect measurement. There are things called "triaxial stresses" under the ball that make it an imperfect measurement, however, it is close enough for bullet casters work.

cbrick

01-17-2007, 02:34 PM

The equation is just a guide, nothing more as it only outlines what would be more ideal than just guessing.

Absolutely, very well said. Anyone casting for very long should understand that there are no hard, fast rules set in concrete. Everything can be manipulated one way or the other for your benefit or detriment. This is one of the things that is so fascinating about this hobby. The 1422 formula is a useful tool when used as a guide.

I think that one of the most useful things about the 1422 formula is that it gets people to think.

Rick

45 2.1

01-17-2007, 02:40 PM

If the peak pressure developed by the load is less than 1,422 x Bhn, you can expect good accuracy (assuming the plain base lead alloy bullet is reasonably well fitted to the barrel). If the peak pressure is MORE than 1,422 x Bhn, you cannot expect good accuracy. You may accidently get decent accuracy and, as mentioned before, there are many ways to "cheat" to move the limit upward, but you cannot routinely expect accuracy.

Harry-
My friends, that i've taught how to do this, and I are positively amazed that we aren't getting good accuracy, either on purpose or by accident, according to you. Your definition must be quite a bit different than what mine is. BTW, that multiplier of three has a counterpart, the upper limit according to the equation providers is the multiplier four. It is just amazing what a little base protection, strengthening or something else does to nulify that equation.

Ricochet

01-17-2007, 02:52 PM

Thank you, Harry O!

cbrick

01-17-2007, 02:58 PM

I am not sure what you are reading. I have both books and both seem to be saying the same thing to me. If the peak pressure developed by the load is less than 1,422 x Bhn, you can expect good accuracy (assuming the plain base lead alloy bullet is reasonably well fitted to the barrel). If the peak pressure is MORE than 1,422 x Bhn, you cannot expect good accuracy. You may accidently get decent accuracy and, as mentioned before, there are many ways to "cheat" to move the limit upward, but you cannot routinely expect accuracy.

That is an exact opposite to everything I have ever read, heard or applied in practice. I'll match my 150 meter cast bullet revolver groups (scoped from bench) against anyone. The accuracy is anything but an accident and the load is way past what it would be using 1422 as a maximum rather than a minimum.

Rick

scrapcan

01-17-2007, 04:36 PM

Well Harry O you beat me to a response, but I will leave my original responsein just for giggles and grins.

Richocet and Harry O,

What you guys just said is what I was getting at. It does no good to throw out an equation without telling what the terms are. I have seen the equation with the seperate terms in several articles/references. But no indication of what those terms may be. If they are seperated out I would imagine somewhere someone will have given them with the definition.

Most of the engineering references give the equation for BHN in SI units and the 1422 is a conversion to get it to US customary units. So if you really want to know I think it would be good to go through the conversion from the SI equation to the US Customary.

Here is website that I found related to BHN testing that may be useful to the discussion fo this topic.

Gordon England website at http://www.gordonengland.co.uk/hardness/brinell.htm

Additional information is found in the machinery handbook.

Good discussion and keep the dialog going.

scrapcan

01-17-2007, 05:28 PM

One thing we all need to keep in mind when talking about this topic is that not all of us are using the same lead alloy in our boolits. The different alloys will have a different stress-strain curve and thus the working pressures may not be the same as that of lead.

We also need to be aware that we are not using precision equipment. Our equipment for measuring BHN may need the different calibration factor in the equation to account for slop in our device (i.e. loading force, ball diameter, time to make indent)

The above formula is away to convert a measurable indent to give a hardness number which is then converted to a psi reading. You still need to know the modulus of elasticity for your alloy to apply what you have calculated. Or you use and approximation (Lee uses the value for lead in his book I think, hopefully someone with one at hand can confirm that) and start from there knowing it is not exact for your material at hand.

Just offering more fuel to keep the fire burning, I offer it as fuel so flame away. I am always open to more learning.

GSM

01-17-2007, 05:37 PM

Here's another discussion of the 14XX * BHN formula.

http://http://www.lasc.us/FryxellCBAlloyObturation.htm

grumpy one

01-17-2007, 05:51 PM

Some clarification might be useful here. When the stress in the bullet alloy exceeds the yield stress, the material enters a plastic state which I have described as goo. Most kinds of goo are viscous, and that is especially true of overstressed metals. Since the whole trip down the barrel only takes a few milliseconds, there isn't much time to change the shape of the goo, and when the goo is also highly viscous, it takes a great deal of stress to reshape it quickly.

Depending on lots of factors, a bullet that is partly in the goo state can perform pretty well - especially if it is wearing a gas check, which keeps its gooiest part fairly flat and square. However whenever there is goo, there is considerable load on the lube. Once the lube fails, the goo can interact directly with the barrel - some goo will then get left behind, implying some flowing around within the bullet to keep replenishing the base area. There are also likely to be bubbles of vaporised lube in there, and they will distort the shape of the goo.

Short summary: a partly gooey bullet can potentially perform either better or worse than a non-gooey bullet, depending among other things on whether the stress exceeds the yield stress by a larger margin than the maximum capability of the lube.

cbrick

01-17-2007, 06:05 PM

Here's another discussion of the 14XX * BHN formula.

http://www.lasc.us/FryxellCBAlloyObturation.htm

I fixed the link for you :-D

Rick

Taylor

01-17-2007, 07:45 PM

not arguing now,nor siding with Lee.Pg 134."Select a load with a chamber pressure that does not exceed the Maximun Pressure in fourth column"
Ex:.indent .058, bhn15.4,bullet strength 21898,Max PSI 19109.I understand this to say: that a bullet cannot tolerate pressure's of more than 21898.He wants to stay about 10% less than bullet strength.

grumpy one

01-17-2007, 08:00 PM

There are several factors here. First, the actual chamber pressure can be higher or lower than that listed in the tables, depending on powder batch, ambient temperature, etc. Second, they are making one statement to apply to all circumstances from plain-base pistol bullets lubed with something scraped off a hot roadway, up to gas checked rifle bullets lubed with Super Unobtainium. I'm inclined to think with almost useless lube, and no gas check, you probably need to refrain from exceeding the bullet strength by any large amount, even when the customer happens to have a fast batch of powder on a hot day. However with a gas check to keep the bullet base flat and square, and a lubricant that might be able to sustain 5,000 or 10,000 psi bearing pressure for some useful fraction of a millisecond, suddenly the "90% of bullet strength" equation becomes ridiculously conservative.

Ranch Dog and others have great success with stresses well above bullet strength. Bass deliberately uses soft bullets - it looks to me as if he's found advantages in having the bullet base in a gooey state under just the right circumstances. It's interesting, though, that Bass ends up with the state and performance of the lube being a big factor in his outcomes.

Bass Ackward

01-17-2007, 08:34 PM

The reason I don't like a formula is because it focuses thought on it and it alone. It stifles growth by establishing mental boundaries. In essence, it supports ..... old wives tales about the limits of cast.

The biggest factors that works against this formula is well known to HV / slow powder users. The faster a bullet can over come inertia and get moving, the more pressure it can take. So therefore, a 22 caliber is easier to start off than a 45 caliber. The slower the powder you run and burn, the more pressure your base can take. The lighter a bullet is per caliber, the higher the velocity potential it has. The larger the case capacity, the slower the pressure comes up. None of these factors is taken into account not to mention throat types, bore condition, lube. Temperature is another big factor.

I have had ACWW over 3000 fps at what many on this board would describe as accurately at slightly over 40,000 psi. That's .... slightly .... above the chart for that hardness. And it took a 22-250 to get it there. For 30 caliber, the highest I shoot 2600 fps with a 160 grain bullet in an 06 and that same mix fails at 34,000 where it craps out. For a 35 Whelen, that drops to 31,000 psi and 2400 fps with a 210 grain bullet or 2200 fps with a 250 grain bullet.

See the trend?

grumpy one

01-17-2007, 09:00 PM

Looks as if its a scale effect then. This is good news. If we switch to .005 calibre rifles we'll be able to make the bullets out of soap. The environmenalists will be pleased, and rifle cleaning can be done just by tossing them in the bath with the kids. Gas check seating might be a bit tricky though.

Harry O

01-17-2007, 09:20 PM

Harry-
It is just amazing what a little base protection, strengthening or something else does to nulify that equation.

Isn't that EXACTLY what I said earlier (the test with plastic shot buffer for a filler). That fact that you can do *something* to skate past the equations limit does not mean it is wrong. What it means is you are comparing apples with oranges.

45 2.1

01-17-2007, 09:26 PM

Isn't that EXACTLY what I said earlier (the test with plastic shot buffer for a filler). That fact that you can do *something* to skate past the equations limit does not mean it is wrong. What it means is you are comparing apples with oranges.

Does that plastic absorb all that pressure or transfer it? It probably increases the pressure potential of the cartridge and increases the pressure placed on the base of the boolit if the manuals are correct. It does work, so just how does that pressure effect the boolit. Apples and oranges, NOT.

Harry O

01-17-2007, 09:30 PM

45 2.1 You obviously have something personal involved in this. Rather than descend into namecalling, you do what works for you and I will do what works for me. End of story.

grumpy one

01-17-2007, 09:31 PM

This is not the only possibility, but seems the most likely one to me. The PSB, consisting as it does of small spheres, is crushable under high pressure. This means it is likely to dull the pressure pulse - creating a slower rise and fall, and lower peak pressure, with the same area under the pressure curve, which translates as muzzle velocity. It is the peak pressure, not the average pressure, which transforms part of the bullet to goo and potentially breaks down the lube.

45 2.1

01-17-2007, 09:38 PM

45 2.1 You obviously have something personal involved in this. Rather than descend into namecalling, you do what works for you and I will do what works for me. End of story.

I don't have and you weren't called anything. Several of us have called you on your statement and you haven't provided an answer that is sound yet. We also know about stress, strain and material deformation as we are engineers also. If you want to do what works for you, fine, then do it and don't relate it as gospel.

felix

01-17-2007, 10:16 PM

The formula as it stands is incorrect for what we are actually discussing. If I read the entire thread correctly, that is. It seems we are talking the same info, but in different words. Have to be careful in remembering such terminology as goo being equal to the plastic state. ... felix

Newtire

01-17-2007, 10:49 PM

Now I see that "Plain Base" has been added to the soup. This changes things altogether I'm getting great groups all day long with about 10,000 PSI over with a gas check. Now the Plain Base...I haven't done enough shooting with those to give an opinion.

grumpy one

01-17-2007, 11:09 PM

Felix, the formula might be correct for unlubricated large-bore plain base bullets under equilibrium conditions. Personally, I think it probably is correct for that situation. When you add gas checks, rapidly changing conditions, lubricants, and scale effects, it is not correct - but it might be the right starting point before applying adjustment factors for those additional considerations.

I think the "plus 10,500 psi" concept is extremely crude. In effect it asserts that all lubricants are equal, all pressure traces are the same shape, and there are no scale effects (or that it only works for one calibre).

felix

01-17-2007, 11:25 PM

Grumpy, yeah. But we still have to remember that the plastic state, the goo, goes up through the middle of the boolit once the boolit is in motion. The nose, if narrow, will see the resulting damage quickly. I'd hate to be the engineer, rather the scientist, to come up with a concrete formulation that would work for almost every situation. I'd probably start with the Swede with it's fast twist because the system in totum has proven to be the most problematic to date on this board. I would probably have boolits made with various concave bases, with checks and without checks, and an exact BR gun made to shoot them. Pressure transducers would be applied throughout the length of the barrel. And, that's just for starters. ... felix

grumpy one

01-17-2007, 11:58 PM

Perhaps we could downsize the effect of some of the variables, though. It might be nice to use a pretty huge bore, so as to minimize the scale effect, because that one would be a whole adventure in itself. If we could minimize the stress caused by rotational acceleration that should help too - not because it is complex but because its interactions with linear acceleration would be complex in a bullet that is partly plastic. Since the plastic part of the bullet acts like a viscous material, and the remainder like an elastic material, the amount of the bullet that is actually participating in the rotational acceleration depends on how much of it is elastic at any given instant.

Suppose we started with a large smoothbore, and made some swaged fluted plainbase bullets for it with just the back quarter inch unfluted? By firing such bullets into a soft recovery medium, we should be able to see how much of the bullet suffered plasticity, from seeing how much of the flutes has decreased in depth. By doing that with various alloys we could test the validity of the formula for plainbase bullets. Next step might be lubricants - which would not reduce the plasticity, but the areas where the lube had failed should be identifiable. Then the whole thing could be repeated with gas checks. Next step would be the same bore size, but with rifling added. Finally, various bore sizes could be used and much the same series repeated. Why, in ten years or so we could have this nailed. What we need is a research grant.

A line from a very old David Frost comedy sketch. Newsreader says, "A ten year government study has concluded that you can make very good money from a ten year government study."

felix

01-18-2007, 12:14 AM

Got money? Now, that's equivalent to saying: Got Milk? I'm game, but we need to recruit Buckshot and/or some other heavy duty folks to shoot that thing you described. We might get some bucks for making a boolit version of a 50BMG BR gun. I'm afraid that monster would have to weigh 200 pounds to keep the recoil in check without using that noise making compensator. We will need 2700 fps pointed boolits, right? Might even have to go up through 3200 to blast out that center. ... felix

grumpy one

01-18-2007, 12:30 AM

It does seem as if the 50 BMG calibre is a good place to start, for a bunch of reasons. Most likely the bulk of the shooting would be done at low velocities - metallurgical examination of recovered bullets should show how far the plastic state extended up the core, and finding whether it actually extends much beyond plasticity of the outside part in such a huge bore would be one of the first results. My guess would be that Bass' scale effect consists mostly of the plastic state extending further up the center of the bullet as the bore gets smaller, for the same height of plasticity on the outside of the bullet.

However, you haven't got the data until you've tested the whole range of conditions, so in the end that monster has to be fired with maximum loads while shooting the hardest possible cast bullets. A hydraulic recoil system borrowed from a really small cannon might be a good idea. Is that autoloading AS50 50 BMG sniper rifle any gentler than a regular AW50? Personally I wouldn't get behind any of them.

357maximum

01-18-2007, 12:44 AM

The reason I don't like a formula is because it focuses thought on it and it alone. It stifles growth by establishing mental boundaries. In essence, it supports ..... old wives tales about the limits of cast.

I have always known the value of ignorance, here it is proving itself yet again....

I load cast to red bullet velocities all the time and beyond always have.. I simply picked a jacketed book load and off I went... It normally worked quite well....Did not know , did not care, did not care to know it was wrong....I knew what I needed to know....it worked....and when everything is right it still does....

The ol 1442 rule is not a rule at all...it is simply a guidline and one I generally choose to ignore or step quite a ways beyond...never was good with rules.:mrgreen:

I have had one major stumbling block in my travels.....

It was with a new encore in 357max...it did not perform the way I thought it should....so I did some reading and got into real trouble..(started listening to the harder=better bs)....my situation worsened the harder I tried and the harder i went... In a total state of frustration I contacted Bob(45 2.1) and asked his opinion.. he suggested I go to a more ductile softer mix......via WQ50ww/50pure.... I honestly thought aloud as I read his email .....*******....as it turned out it was I who the ******* be..[smilie=1:

I tried it....Bingo it worked. I have since used that alloy in many scenarios with great results...so I agree with the fellas stating that knowing that the GUIDLINE exists is great.....but do not live your life by it ....

I take the ditchdigger approach it either work or it don't...most the time it do...if it do not something else is probably wrong....

I am currently pushing a redneck plainbased 7mm lee boolit in a .280 rem.. waaaay harder with moa accuracy than any "RULES" say I can...I did not know if it would work...thought maybe it very well wouldn't....but instead of crunching numbers , reading, mind f 'ing it to death and sitting around thinking and contemplating, I got up off my **** loaded some test rounds and went out and actually tried it....it worked just dandy...came back in and loaded 50 of the best load, and went out and shot them all just to make sure.....yep still there...nice little cloverleafs...

Hypothetical fancy math does not cut it for me....I am more of a seat of your pants fella,,,, but to each their own....

****Disclaimer***The proceeding was one simpletons opinions and if for some reason you feel yourself totally disagreeing with his post...please be aware....more than likely he do not care, or care to know, or know enough to care..

Michael

felix

01-18-2007, 01:20 AM

Michael, you are absolutely correct! Happiness is keeping things we enjoy on a hobby level, and there is no doubt about that. ... felix

45 2.1

01-18-2007, 07:35 AM

piwo

01-18-2007, 11:11 AM

I have always known the value of ignorance.....

.....Hypothetical fancy math does not cut it for me....I am more of a seat of your pants fella,,,, but to each their own....

Michael

heehee.. this reminds me of a quote from Hall of Fame pitcher Bob Gibson, who when told by a reporter that a scientist concluded that curve balls don't really curve, it's an optical illusion: " tell him to go stand behind a tree and I'll bounce optical illusions off his head all day".. Quote probably isn't word for word, but you get the idea....

Not to belittle the science though. I find it fascinating and a place to frame my projects and expectations. I wish I understood it more. Unlike the learned men here, I am not an engineer, and don't possess even the basics of metallurgy, except that if its liquid metal, it's probably hot, and if a big chunk hits you, it will probably hurt. :oops:

ktw

01-18-2007, 11:53 AM

One does not need to run tests on anything here, it has already been done for you. Simply go to the Lyman manual (one that has pressures listed) and view the 44 mag section. A nice plain based boolit (the 429421 is good) is shown and look at the results. It shows the boolit going above the 1422xBHN maximum quite a bit. Does anyone say that they are not accurate?

Roughly 10% more than 1422xBHN at the top end, based on their specified alloy (Linotype).

I think this tends to support the observation made earlier by Ranch Dog; that during early load development work with cast boolits, the portion of the pressure curve in the vicinity of 1422xBHN is an interesting place to start. Particularly in the case of the larger caliber, plain-based slugs (the situation I outlined at the beginning of this thread).

I agree with many of the comments made earlier that shooting cast boolits is largely an experimental undertaking - there aren't a lot of hard and fast rules to live by here. At the same time, the materials we are working with do have limits and I find the technical give and take useful in that it does lead to a greater understanding of the materials and can guide us into more productive experimental paths.

Thanks again for the discussion.

-ktw

scrapcan

01-18-2007, 11:54 AM

KTW Good post and I agree whole heartedly. The scientific method can help to refine the question at hand.

Treeman

01-18-2007, 11:55 AM

Grumpy, Would you be satisfied with skipping the testing and simply rechristening boolits as 'Visco-elastic ballistic putty' ? ;)

grumpy one

01-18-2007, 07:26 PM

Treeman, I don't think the new name provides as much detail as the experimental results would. As a fine point, the bullet material is only putty when it is in goo mode - i.e. stressed above its yield point.

45.2.1, as KTW has said, I don't think a nominal maximum gas pressure 10% above the nominal yield stress of the material generates any discord with the theory - it just gives you a number for how much pressure the lube is supposed to be able to tolerate momentarily. I guess they are talking about the lube they recommend for that application in that manual.

45 2.1

01-18-2007, 09:35 PM

45.2.1, as KTW has said, I don't think a nominal maximum gas pressure 10% above the nominal yield stress of the material generates any discord with the theory - it just gives you a number for how much pressure the lube is supposed to be able to tolerate momentarily. I guess they are talking about the lube they recommend for that application in that manual.

Well, you can believe that 10% or not, but compare the 44 mag rifle section against the 44 mag pistol section in the 48th manual. The pistol alloy is linotype (suprise) and the rifle sections alloy is #2 alloy. Compare like lead boolits and like loads. You'll find the same loads on most, like 429667 (429421 isn't on both) with 2400 at 20.6 gr. gives 38,900 C.U.P. in the pistol section. There will probably be a slight pressure difference between alloys, but lintoype at 21 BHN gives 29,862 for pressure and #2 alloy at 17.5 BHN gives 24,885 for pressure using the "formula". Both are well below the listed pressure. One load is 30% over and the other is about 56% over. I've seen enough things like this to not believe any formula like that given. If you choose to believe and follow the formula, you will be limited in what you'll try and miss some very interesting things as 357 maximum found out. Its your choice.

grumpy one

01-18-2007, 09:58 PM

I don't disagree with you - the science aspect is not nearly far enough advanced to replace practical experience. Bearing in mind that the science says there are several crucial factors not yet mapped - the gas check effect, the scale effect, the performance of various lubricants, and the time lag effect (how quickly does the plastic state propagate through an overstressed metal?) the formula is not even a starting point unless you have a large bore, plain base bullet with a pretty undistinguished lube. Even then it is a point to work up from, not a point to work down from.

Way back when I was in training there was a lot of interest in an experimental manufacturing process called "explosive forming" - you shaped what was initially a flat sheet by using a one-sided die, and an explosive charge in a largish cavity on the opposite side. The first and most obvious thing that was found when forming steel that way, was that you were dealing with gas pressures that were much higher than what the strength of materials calculations predicted would be required. Some of this was just due to geometry - you can only form the part of the sheet that has yielded - and some was due to timing effects - explosive pressure delivery takes a finite amount of time, and during that time pressures vary greatly in the forming cavity. However that didn't seem to explain it all.

Ricochet

01-19-2007, 10:15 PM

That's interesting. I've read that the anode plates of General Electric's 1960s 6L6GC vacuum tubes were made of a multilayer metal sandwich put together by explosive forming like that. A recent commercial reproduction of those tubes was to use leftover old material, but the stuff's no longer made.

grumpy one

01-19-2007, 11:48 PM

Some frame rails for low-volume cars, and similar items made from tubular stock, are produced by hydroforming these days. That consists of putting an external die around the tube, and applying internal hydraulic pressure until the tube conforms to whatever shape the die is. Depending on the formability of the material, that seems like a better way to make a tubular anode. Having said that, if the stuff is only formable at explosive speeds for example, that's a new ball game. They must have had some reason to do it the way they did.

Ricochet

01-20-2007, 12:25 AM

My understanding was that the explosive was used to weld together the layers of different metals in the sheet, not for forming the structure.

grumpy one

01-20-2007, 02:02 AM

We probably have different definitions of explosive forming. There is a process called thermite welding which would be in line with your description.

MtGun44

01-20-2007, 02:27 AM

I am going to make one more try at this "goo mode" claim. Just because
a metal is loaded beyond the linear portion of the stress strain curve
does NOT turn the metal into "goo". This is absolutely hard scientific
fact. "Goo mode" is not factual and does not happen.

All that happens at the yield point is that some of the deformation becomes
permanent, rather than springing back to the original shape after the
load is removed. That is ALL that "reaching the yield stress" means.
The metal is still just as strong as it was just below the yield stress, but
the relationship between load and deformation is no longer linear. For
many metals, the material actually gets stronger as you load it beyond
the elastic limit -- this is called work hardening and the metal is permanently
strengthened.

Check out the attached stress strain curve. This would be appropriate
for steel or aluminum. Lead alloys would be very similar, but my
professional experience with actual stress strain curves of lead alloys
is mostly for eutectic solder (63% tin-37% lead) which has only a moderate
work hardening effect. I'm not sure what our low alloy lead alloys would
do as far as work hardening, but I have heard of work-softening of
*heat treated* lead alloys, but this is not the same as work hardened.

I'm no expert in the interpretation of the 1422xBHN formula, and while
a fairly experienced caster by some standards, I'm still listening and learning
from this group - but we do need to stick to the scientific facts when they
are known, and the meaning of yield stress is very well known.

And it isn't "turning to goo".

Bill

Bret4207

01-20-2007, 09:38 AM

WOW! You won't find discussions like this at "Billy Ray Bob's Hunting, cat fishin' and NASCAR" website! Excellent.

Some of this is wayyyyy over my head. The idea I'm getting is that this formula is a guideline for determining APPROXIMATELY when a plain base boolit will start to obturate. My question would be this- If the alloy begins to deform at such and such a pressure, doesn't the time the pressure remains at that level have a significant effect on the issue? IOW- if the pressure stays high enough for a longer period of time then more obturation takes place? Assuming the obturation in our particular case is bad (nose slumping for instance) then slower powders would seem to be a good thing. Am I following that right?

Also, is the effect of the lube and groove design a factor at all? If a particular lube supports the grooves and remains in the grooves for a longer period of time doesn't that affect things like the obturation? It's all boolit fit right?

I'm in the crowd that says "Try it and see". I'm not a high velocity type anyway, but this thread brings up questions. I have a gut feeling that firearms vary so much that the formula is no more than a loose guideline. There is so much that can cause differences in pressure and so few guys who actually figure the pressures, much less those with Personal Ballistics Laboratories with it's transducers, etc, that I wonder if any of this is really going to clear things up for guys like me.

One things for certain. I wish I had paid more attention in school!

Taylor

01-20-2007, 09:52 AM

I'm with you Trp Bret,some of this is way over my head,so I just pick out the word's I can read and go from there.But this discussion has given me a much better understanding of 1422 and bhn.Just shoot them and don't worry about it.

felix

01-20-2007, 11:28 AM

Guys, it isn't over ya'lls heads. It's the terminology that sucks. And, with the new generation of folks the terminology is going to continue going south. For example, a mouse. Now, what the hell is that? An animal, or a plastic gadget with or without a tail, err... a wire, a radio transmitter, or just what. Will somebody clue me in? It's over my head, err.... that's water pressure several years ago, or is it something on top of a person's neck? Maybe something else all together if you read Playboy. Yes, Latin was once considered the ideal language because it is/was considered to be non-progressive and static enough to be "concrete" in meaning. ... felix

mag_01

01-20-2007, 12:49 PM

------BHN x 1422 = the ultimate compressive strength of the boolit-----this is the strength of the boolit---what it can take in pressure before it start to deform---and max chamber pressure should be about 10% less to be on the safe side. Lets say you have a BHN of 16 x 1422 =22703 PSI so a max chamber pressure 10% less would be---20433---this would be the max chamber pressure to insure the boolit of 16 BHN is at least 10% below the level at which permanent deformation occurs. Pressure not velocity dictates boolit strength. The best accuracy seems to occur just before the (UCS). ------Elastic limit boolit returns to its original size. Hope this helps----Mag

floodgate

01-20-2007, 02:04 PM

Grumpy:

No, there IS an explosive welding process. It (or at least one version thereof) had been developed by an inventor at China Lake where I worked in the early 1960's, and he wrote a book on the process. Photomicrographs of sectioned welds between two plates slapped together by a sheet explosive showed "breaking wave" type interlocks between the two dissimilar metals not normally weldable together. He heard the Russians had translated and adopted his book - without offering royalties - and asked the State Department to look into it. Eventually, he got an answer from the USSR, inviting him to come to Moscow to collect his fees. Since that was the height of the "Cold War", he decided to pass on the invitation.

floodgate

Ricochet

01-20-2007, 03:20 PM

We probably have different definitions of explosive forming. There is a process called thermite welding which would be in line with your description.
Oh, I'm familiar with thermite welding. No explosives involved with that.

joeb33050

01-20-2007, 03:38 PM

We did a lot of work on this, and at least some of us have concluded that there is no relationship between pressure, accuracy and bullet hardness other than that more speed requires more hardness, in steps such as: up to ~1200 fps, any alloy; ~1200-1600 fps, WW at ~12 BHN; ~1600 fps to ~2200 fps, linotype or so.
Now this flies in the face of a lot of published work, but I believe it's mostly wrong.
See 3.3.1, 3.3.2, 3.3.3 in the book at http://sports.groups.yahoo.com/group/CB-BOOK/, free to all, -there's a pretty comprehensive list of articles about this in there.

Particularly irritating to me is the notion that accuracy falls off with a given pressure as hardness goes both below and above the "calculated" "proper" pressure; and the many references to "ultimate compressive strength" and "compressive strength" that don't apply to lead alloys.
I'm not here to get into a contest, everything I and the others have to say on the matter is in the book.

joe brennan

MtGun44

01-20-2007, 06:14 PM

Tpr. Bret,

This is not rocket science, but some of the terms are unfamiliar. Ask most folks
what groove diameter, twist rate or headspace are and they'd be baffled,
yet all experienced cast bullet loaders know exactly what they mean and try
to use these terms and knowledge about them to get more accurate loads.
As we learn new terms we get more able to understand what is going on
and hopefully make better loads.

One commonly made statement which 45 2.1 has pointed out as incorrect
is that going above 1422 X BHN is necessarily a bad thing. If the bullet
is undersized, it must be bumped up to fit the bore to seal it and be
properly guided by the bore. We all have seen "too hard" bullets with
light loads shoot poorly and lead like mad. In this case MORE pressure is
needed to make the bullet obturate and fit the bore. OTOH, if a bullet is
too soft and the pressure is way too high, the pressure can distort the
bullet too much, and if the lube isn't working or the quantity (groove volume)
is inadequate, you will not be pleased there either. So - too little pressure
can be bad sometimes and too much pressure can be bad sometimes. It
may be helpful to know at what pressure the bullet will begin to permanently
deform (yield), but it isn't some guarenteed peg point to either never go
over or never go under. As usual "it depends. . . "

"Try it." is a very good point made by many here. :-D

As far as the nose slumping - The base the bullet is subjected to the pressure,
and the whole bullet is subjected to some really serious acceleration forces
(Gs just like the astronauts - now there you'd get some goo if you subjected
a person to bullet level Gs!). I'd guess that the main load on the nose would
be acceleration forces, which if high enough could cause the whole bullet to
reach yield - not from the pressure loads (which we'll not consider for this
point, but they are still there) and this might cause slump. I have no
experience with loads that high and alloys that soft, but maybe
some other folks have some knowledge about that. :confused:

The lube and groove design have to be factors, and 45 2.1 has pointed out
that if a bullet has a small enough area at the grease groove, it could yield
under pressure and this would make the groove volume try to decrease,
forcing the lube out and helping lubrication. I believe that Glenn has pointed
this out in one of his (excellent!) articles, too.

Bill

MtGun44

01-20-2007, 06:24 PM

grumpy one

01-20-2007, 06:52 PM

Ricochet and Floodgate, I don't see in principle why applying explosive force to two sheets of metal pressed against each other should not have much the same effect as a blacksmith's forge-welding process. Deformation of metal in the goo state (i.e. yielded) generates a great deal of heat, which can be calculated by multiplying the stress level by the displacement of each infinitesimal element of the metal - it is a form of viscous drag. Deformation of any viscous material requires energy input, and the energy is transformed into heat. The explosive itself also delivers heat. If practical experiments show that in practice this can actually be a useful welding process, that is interesting - I'd never heard of it.

45 2.1

01-20-2007, 07:30 PM

------BHN x 1422 = the ultimate compressive strength of the boolit No No No, it is the point where it yields, i.e. the yield strength where permanent deformation starts takeing place with no loss of material strength, the multiplier on the conversion constant is 3. What hasn't hardly been mentioned is that there is an upper range for the formula where the multiplier is 4, which they say is the ultimate strength of the boolit, a point where any more pressure actually decreases the strength of the material. And i'm still not defending the "formula", just telling you what its supposed to mean.-----this is the strength of the boolit---what it can take in pressure before it start to deform---and max chamber pressure should be about 10% less to be on the safe side. Lets say you have a BHN of 16 x 1422 =22703 PSI so a max chamber pressure 10% less would be---20433---this would be the max chamber pressure to insure the boolit of 16 BHN is at least 10% below the level at which permanent deformation occurs. Pressure not velocity dictates boolit strength. See the above, this is not quite correct. The best accuracy seems to occur just before the (UCS). ------Elastic limit boolit returns to its original size Elastic limit is below 1422xBHN. Hope this helps----Mag

357maximum

01-20-2007, 08:16 PM

WOW! You won't find discussions like this at "Billy Ray Bob's Hunting, cat fishin' and NASCAR" website! Excellent.

.... ya might be a bit surprised......

floodgate

01-20-2007, 08:33 PM

grumpy:

It's out of my range for sure, and probably out of yours too, but here it is on AbeBooks:

Explosive Working of Metals
John S. Rinehart , John Pearson
Bookseller: Zubal Books
(Cleveland, OH, U.S.A.) Price: US$ 470.45
(£ 238.37)
[Convert Currency]
Quantity: 1 Shipping within U.S.A.:
US$ 5.50 (£ 2.79)
[Rates & Speeds]
Book Description: Macmillan 1963, 1963. 351 pp., hardback, minor ex library marks, else text and binding clean and bright. Bookseller Inventory # ZB516841

[Bookseller & Payment Information] [More Books from this Seller] [Ask Bookseller a Question]

floodgate

Bass Ackward

01-20-2007, 08:39 PM

Well, I se that this is still going. Thats great. It's very educational.

I just spent the day running some formula busting 20-1 and ACWW that should make linotype puke. Here is my copy. Hope it prints properly.

Pressure Ranges for Lead Formulas

This is the formula for making the Calculations: ALLOY: BHN X Tensile Strength (480) = Factor, Factor X 3 = Minimum Chamber Pressure (psi), 4 X Factor = Maximum Chamber Pressure (psi)

Examples for common mixtures:

PURE
LEAD 5 5 X 480 =2400, 2400 X 3 = 7,200 psi, 2400 X 4= 9,600 psi

1-20 LEAD / TIN 10 10 X 480 = 4800, 4800 x 3 = 14,400 psi, 4800 X 4 = 19,200 psi

WHEEL
WEIGHTS 12 12 X 480 = 5760, 5760 X 3 = 17,280 psi, 5760 X 4 = 22,040 psi

LYMAN
#2 15 15 X 480 = 7200, 7200 X 3 = 21,600 psi, 7200 X 4 = 28,800 psi

LINOTYPE 22 22 X 480 = 10560, 10560 X 3 = 31,680 psi, 10560 X 4 = 42,240 psi

HEAT TREATED
WHEEL WEIGHT 30 30 X 480 = 14400, 14400 X 3 = 43,200 psi, 14400 X 4 = 57,600 psi

grumpy one

01-20-2007, 09:26 PM

grumpy:

It's out of my range for sure, and probably out of yours too, but here it is on AbeBooks:

floodgate

Thanks Doug, I'm a regular user of Abebooks, both for academic literature and sci fi I can't find anywhere else, but I think $100 plus postage is my record so far, and that was for something I needed desperately. In this case I'll restrain myself. Appreciate the reference, though.

joeb33050

01-21-2007, 07:19 AM

Joe,

For the folks like me that don't understand how to get the free book,
but would like to read it and learn, can you give us a simple "how to
get it" post? Is it a download? I don't know anything about Yahoo
groups and what/how to do with them. Sorry to be ignorant but never
dealt with that before.

Thanks.

Bill

Bill;
If you go to my post above and click on the address, it takes you to the site. There's a little signing in, the book is in FILES with a table of contents at the beginning. I'm not a computer guy myself, let me know if you have trouble.
Thanks;
joe brennan

longbow

01-21-2007, 04:43 PM

It seems that this is a controversial subject and one with lots of opinions as to which matters more - the formulas or field results.

I thought I would jump in with my 2 cents worth here too.

Bass has some good stuff above and to expand on the info and sources for lead properties I have a report published in 1955 by the Consolidated Mining and Smelting Company of Canada Limited (subsequently Cominco, now Teck Cominco). I used to work for them. now I work for a consulting company that works for them - ya just got to love corporate take overs and mergers (this is my 3rd)!

Some of the data is directly applicable to the bullet hardness and strength discussion in this thread so I will pass on those tidbits. If anyone is interested I can have the tables scanned as jpeg's or PDF's.

properties of pure lead @ 99.73% pure:
tensile strength: 1700 - 1900 PSI (sand cast); 2000 PSI (chill cast - likely similar to our type of bullet casting)
Brinell hardness: 3.2 to 4.5 (sand cast); 4.5 (chill cast)

Now, the number of 480 that is mentioned here and in other sources is what you get when you divide the tensile strength by the Brinell hardness number.

In this case it is: 2000/4.5 = 444. It is not exact and varies with alloy hardness to an extent.

Properties of lead with 4% antimony:
tensile strength: 4020 PSI (cold rolled); 11670 PSI (heat treated at 450 deg F then quenched)
Brinell hardness : 8.1 (cold rolled); 24 (after heat treating)

Properties of lead with 8% antimony:
tensile strength: 4650 PSI (cold rolled); 12350 PSI (heat treated at 450 deg. F then quenched)
Brinell hardness: 9.5 (cold rolled); 26.3 (after heat treating)

For the "480" number: 4650/9.5 = 489 and 12350/26.3 = 470 so a little variation but close.

You can see that even heat treated 8% antimonial lead only has a tensile strength of 12350 PSI which is very low by firearms standard chamber pressure considering that a .38 Special SAAMI rating is 18,900 CUP (according to my Speer handloading manual).

From my readings, the "480" is a number used by C.E.Harris where he recommended that chamber pressure be at least 3 times the tensile strength of the boolit alloy and up to 4 times the tensile strength of the boolit alloy as a guideline. The "480 is derived from the tensile strength/Brinell hardness number.

I have seen "500" used for this purpose as well and it is approximate.

So, what you get for heat treated 4% antimonial lead is: 480 x 3 x 24 = 34,560 PSI (min. recommended chamber pressure) to 480 x 4 x 24 = 46,080 PSI (max recommended chamber pressure)

If you want to use the 1422 x BHN: 1422 x 24 = 34,128 PSI (in the same range as above). The 1422 is derived from the conversion from metric units of the induced surface stress during the BHN test and again is approximate.

What these answers give is a recommended CHAMBER pressure NOT the tensile or yield strength of the boolit alloy.

My understanding of the formulas above are that they were derived from field results as a guideline for developing loads. They have been recommended by several gunwriters as a method for developing cast boolit loads by starting with appropriate chamber pressures. I do not think they are considered the final word but used for a starting point and general guideline.

Another issue here is what actual pressure the base of the boolit sees. The base of the boolit is exposed to the burning powder but there are losses of pressure all down the barrel due to the first lit powder in the breech pushing the boolit and the rest of the powder down the barrel as it is burning, and there are friction losses through gas turbulence, increasing volume, etc. in the barrel as well. In a straight walled cartridge and large bore the losses would be small but in a bottle neck case they would be fairly large.

What actual pressure does the boolit see? I don't know. Maybe someone with a piezo pressure transducer can hook one up at the breech to check then maybe half way up the barrel (it it is doable). Certainly chamber pressure doesn't peak until the boolit is on its way though fast pistol powders peak quickly.

Anything above the base of the bullet sees less pressure because it is accelerating less mass and of course the nose sees only compression from the air and small acceleration forces.

Even a .38 Special produces enough pressure to to turn a hard boolit to a solid smooth slug if the boolit were contained (if it couldn't move). The fact that the boolit can accelerate up the barrel keeps it from being swaged into a solid smooth slug.

Think about .44 mag pressures of 30,000+ PSI even with a hardened boolit with a tensile strength of 12,350 PSI the tensile stress is being exceeded by 2 1/2 to 3 times. If the boolit couldn't move it would be swaged to a smooth cylinder.

Well, I guess I have to qualify that statement to: if there were no lubricant in the grooves the boolit would be swaged to a smooth cylinder.

There is an article I think on this site that describes a fellow swaging hard cast boolits in a press to a new shape (hollow point? Nose shape change? I can't remember) and he said it worked fine as long as there was lube in the grooves, if not the grooves collapsed.

If the applied pressure exceeds the tensile strength of the material it changes shape to its surroundings. Obviously the majority of the boolit does not see the full chamber pressure.

There are things going on here that would take a physicist years to sort out but people have been casting boolits for guns and shooting them successfully for several hundred years.

I have several articles by C.E. Harris (some passed on to me by Dale53) and David Southall among others. There is also a website (Los Angeles Gun Club I think) with good info by Glen Fryxell (I hope I spelled that right).

Do I have it all figured out - no! But I have fun trying things and am currently working up loads for my .303's and will be following the recommendations of C.E. Harris and David Southall since they seem to get better results than I have so far.

Maybe that will help clear things up and maybe not. Just do what works for you.

Longbow