Pressure curve or acceleration curve?

[leftiye]

Been reading B.A.'s Secret of HV Cast. Damn fine exploration of a hard to lay out bunch of concepts. I didn't know if this would "fit"well if placed on that thread, so I started a new one.

B.A.'s thrust seemed to me to consist for the most part of a number of ways to keep boolit deformation to the minimum. Especially the use of slower powders to delay the pressure peak, along with several other ways to delay same. Well I got to thunkin' about this, and came up with a question. :confused:

If you read enough B.A. (different from B.S.!:mrgreen:) you know he isn't talking low pressure. He takes every opportunity to decry the "1400 X BHN" rule. So why does delaying the peak pressure until the boolit is down the barrel some make any difference if the pressure is above the plastic limit of the lead? Especially when he even goes to softer lead in order to go faster. Is it because the boolit is well supported by the barrel? I'm sure that is some of the answer. I'm sure that some of it is also that right at the first is the only place that all of the pressure bears on a boolit that is stationary, and the pressure therefore directly deforms the booit.

Then I had a possible clue. It may be because the boolit is accelerating at a slower rate later in the barrel than it is right at first. Traveling faster, but accelerating at a lower RATE? Therefore, less "G" force upon the frontal parts of the boolit pushing back against the base of the boolit.

Does anyone have data as to how fast a boolit is traveling at different points in the acceleration down the barrel? Can anyone calculate how the "curve of G forces" of a fired boolit might look? If acceleration is what causes deformation, andI'm sure it is, then we need to modify the rule of 1400 X BHN to read in units of acceleration.

[felix]

Actually, the velocity of the boolit is a function of the SUM of all microscopic pressure points along the barrel behind the boolit. What BA implies is that at the MAX pressure micropoint, the pressure is quite low for a slow powder versus that of a fast powder. The point would never be the same for powders of different speed (everything else the same). ... felix

[Larry Gibson]

"Then I had a possible clue. It may be because the boolit is accelerating at a slower rate later in the barrel than it is right at first. Traveling faster, but accelerating at a lower RATE? Therefore, less "G" force upon the frontal parts of the boolit pushing back against the base of the boolit. " The longer it takes to get to speed in the barrel the less obturation. Lengthening a time/pressure curve has nothing to do with reducing the pressure.

You have grasped the point, which is why many of us use medium and slow powders for cast bullet speeds in rifles above 1600 fps or so.

Larry Gibson

[leftiye]

Felix, Only if the actual peak pressures were different (no C.U.P.'s allowed) would that be true. I recognize that at peak cast velocity for the faster powder that the slower powder would create lower pressure, but he then jacks up the speed some more, and the difference in pressure may not end up being that much after all. Also, remember that he's exceeding the plastic limit of the metals in both cases.

Is there a way to calculate acceleration from two speeds and the time elapsed between them? I imagine we'd get pretty theoretical because speed at different places in a bore would be calculated in the first place. Also, the elapsed time would probably have to be estimated by Calculus. Might be worth having an idea how the acceleration situation looks as well as the pressure curve.

[Bass Ackward]

Leftiye,

I think you want to look into a computer program called Quickload. It does all that you are asking and more. It's expensive, but with today's component prices, it paid for itself in 6 months for me.

[joeb33050]

Actually, the velocity of the boolit is a function of the SUM of all microscopic pressure points along the barrel behind the boolit. What BA implies is that at the MAX pressure micropoint, the pressure is quite low for a slow powder versus that of a fast powder. The point would never be the same for powders of different speed (everything else the same). ... felix

I keep reading this stuff, and it keeps making no sense. What does it mean, "Actually, the velocity of the boolit is a function of the SUM of all microscopic pressure points along the barrel behind the boolit"??? Does it mean anything?
The velocity of any given bullet is a function of the area under the pressure curve, from ignition to muzzle or maybe a little after. The counters are inertia and friction. That's it kids, unless Felix has repealed F = MA.
Is it BS, or is it me?
joe b.

[joeb33050]

"Then I had a possible clue. It may be because the boolit is accelerating at a slower rate later in the barrel than it is right at first. Traveling faster, but accelerating at a lower RATE? Therefore, less "G" force upon the frontal parts of the boolit pushing back against the base of the boolit. " The longer it takes to get to speed in the barrel the less obturation. Lengthening a time/pressure curve has nothing to do with reducing the pressure.

You have grasped the point, which is why many of us use medium and slow powders for cast bullet speeds in rifles above 1600 fps or so.

Larry Gibson

Since I can't find the beef in this I've become somewhat abrupt. I don't mean to offend anyone. Well... However, I just have to ask this question. Larry, medium or slow powders at higher velocities? Do you think that this is news? Don't we all know this? It ain't news!
Am I wrong?
joe brennan

[Larry Gibson]

Joe

Take a valium, relax and enjoy the morning. Maybe get another cup of coffee.

Not everyone is aware of every thing. No, medium and slow powder use with cast bullets for higher velocity has been around for longer than me (don't know about you). And NO, we don't all know it. Look at Lyman's, RCBS's and other manuals and you will find the predominant use of fast powders for low velocity cast bullet loads in rifle cartridges. Read current magazine articles, of which there aren't many these days, on shooting cast bullets (other than in BPC's) in rifles and in most the use of fast powders at slow velocities is all that is mentioned. Show me in any current manuals where ANY instruction is given in loading slow powders for accuracy at higher velocity with cast bullets and why it works. There isn't any so save yourself the time.

Leftiye brought up a question and it was answered. That's part of what a "forum" is; a discussion. Also in a "discussion" all sentences are not going to be "declaritive".

Larry Gibson

[felix]

Leftiye, you're not wrong! If I am not mistaken, it was Ray Scarborough at Johns Hopkins who developed the Calculus for the big 16 inchers way back when. He also relied upon his expertise in numerical analysis in supporting his derived functions. ... felix

[Harry O]

I thought about this some myself. However, I don't really agree with your conclusion. I am thinking that what you are seeing has something to do with impact load vs a more gently applied load. I know from when I was doing testing on truck-trailer parts (years ago) that impact loads had a MUCH greater effect that an equal load that was more gently applied. Even if it was only slightly more gently applied.

I think everyone can agree that black powder could be considered an impact load. It is also relatively low pressure. I depend on that with my 41 Long Colt bullets. They have to slug-up from 0.386" to 0.401". I found out that Bullseye doesn't do nearly as good a job as BP and Unique does evern worse a job of slugging things up.

Since I was concerned about blowing up 100 year old guns, I carefully checked what was listed as the pressure of each so I wouldn't overstress it. I was getting better bump-up from BP even though it was supposed to be less pressure.

[Larry Gibson]

Harry O

Realise that the time pressure curve of the BP, though not as much peak pressure, is much quicker than the T/P curve of either Bullseye or Unique. I will grant you that impact load is much more severe but you don't have an "impact" per se as nothing is impacting the base of the bullet. The gas pushes on the base of the bullet. How hard that push is depends on how fast the T/P curve builds. As objects at rest tend to stay at rest is why the bullet will obturate when accelerated. The alloy will set back and swage out to fill any voids (in the lube grooves, in the space between the bullet and barrel and into any voids in the casting) if the accelleration is fast enough. This is why we harden bullets; to resist this obturation during accelleration. Some believe it is to "hold" the rifling to keep from stripping but that is not the case. We harden the bullet so it will keep its form during accelleration and not set back or improperly obturate. Using a slow powder and lengthening the T/P curve allows a higher velocity before unwanted obturation takes effect.

Larry Gibson

[leftiye]

Larry, I agree. Harry is on the right track too, he just has to percieve impact as fast time/pressure rises, and also look at mass with it's accompanying inertia as the resistance/obstacle.

Black Powder is a true explosive and generates a shock wave (smokeless doesn't detonate, it burns, and does not create a shock wave, as it is not an explosive in the true sense) which equates to a much faster pressure rise and much more "impact." Slowing down the pressure rise could be seen as lessening the impact, though the true perspective is that we are looking at lessened internal pressure on the boolit from lessened acceleration pushing against the inertia of the frontal parts of the boolits.

It would still be nice to know how much acceleration (rate) a specific alloy can withstand before plastic deformation occurs. If we knew this we could also know how much pressure rise over time would cause deformation and we could choose loads by pressure curve for particular alloys. I think these variables can be derived from existing data, and therefore not require a huge amount of experimentation.

This amounts to the answer as to why the 1400X BHN rule is inadequate. If you can avoid the initial pressure before the boolit moves from exceeding 1400XBHN you can exceed it later in the acceleration of the boolit. Just so long as the rate of acceleration does not cause the amount of internal pressure developed against the inertia of the front of the boolit to exceed 1400Xbhn.

[Bass Ackward]

This amounts to the answer as to why the 1400X BHN rule is inadequate. If you can avoid the initial pressure before the boolit moves from exceeding 1400XBHN you can exceed it later in the acceleration of the boolit.


Leftie,

Now you are thinking.

In a 35 caliber, I can make 14 BHN last to 34,000 psi with a 210 grain bullet at 2400 fps. 33,000 psi with a 220 grain at 2300. A 250 grain reaces peak accuracy at about 31,500 to 32,000 psi at 2100 fps. That is with a case volume of and a shape of a 35 Whelen case. GO to a 358 Norma and I can show you MORE from 14 BHN.

But if I drop down to a 150 grain in the 30-06 case in 30 caliber, I can get 35,000.

Drop to 22 caliber, I can make 40,000 psi from ACWW from a 48 grain in a 223 at 2850 fps. Or I can show you 3200 fps with a 22-250 at the same 40,000.

If I increase the case volume to bring the pressure up more slowly, I can do better. That's why that formula isn't worth much except for handguns, and only as a starting guideline.

What you are actually looking at is acceleration and pressure curves derived from overcoming inertia. The old pump up a bicycle tire or a tractor tire. The bicycle tire needs 40 psi and pumps up quick where the tractor tire may only need 12# of air and take you all day. That's case volume. Bullet weight is a bank vault door. You can take a bank vault door and push it closed with one finger. Attempt to kick it closed, and you will break your leg.

[Harry O]

Larry, I agree. Harry is on the right track too, he just has to percieve impact as fast time/pressure rises, and also look at mass with it's accompanying inertia as the resistance/obstacle.
..........
It would still be nice to know how much acceleration (rate) a specific alloy can withstand before plastic deformation occurs. If we knew this we could also know how much pressure rise over time would cause deformation and we could choose loads by pressure curve for particular alloys. I think these variables can be derived from existing data, and therefore not require a huge amount of experimentation.

This amounts to the answer as to why the 1400X BHN rule is inadequate.

I believe that the "steepness" of the time/pressure curve is a measure of the powders "kick". I disagree that the bullet base does not see an "impact". Pressure is the same whether it is from gas or from a hammer. The only difference with gas is the steepness of the time/pressure curve.

What I have been pointing out is that there is plenty of information out their on pure lead stress vs strain curves. It answers many of the questions you are asking. You just have to listen to what it is saying. Unfortunately, I have not seen very many curves for lead/tin (except for 50-50, 63-37, and 95-5, which are for soldering, not casting bullets -- and, believe me, I have looked).

What they show is that any amount of pressure will cause some strain. Below the "yield point", the stress and strain are directly proportional. Double the stress and double the strain. In addition, remove the stress and the strain will disappear -- when the bullet leaves the barrel, it will return to the same size it was before (except for rifling, etc). When you exceed the yield point, the stress and strain are NOT proportional. As long as you keep the pressure on (above the yield point) the more strain will occur. In addition, when you remove the stress, the strain will NOT disappear. You will have a deformed bullet and the most deformation will be at the base -- where the stress was applied.

What I believe is that you need a CERTAIN amount of deformation during the trip through the barrel to seal the rifling. That can be done below the yield point. If you go over the yield point, the base will deform leading to poor accuracy. BTW, the Bhn number gives a pretty close number for the yield point (triaxial stresses screw it up a bit, but not that much -- besides I believe that the stresses a bullet sees when it travels down a barrel ARE triaxial stresses)

I agree that the 1,422 number is NOT the entire answer, that there are "exceptions". In a previous post I called them "tricks". Whatever you want to call them, I know that you can go higher than that. But you cannot without changing something to soften the blow on the base of the bullet.

What has worked for me is using 1,422 as an upper limit. That way I don't get deformed bases. I also use about 2/3 to 3/4 of the 1,422 number as my lower limit. Lower than that and the rifling won't seal.

[Nelsdou44]

Very interesting read.

One item I have not seen discussed is the influence of the work needed to engrave the boolit into the lands in regards to the pressure/acceleration curve.

The boolit yields permanently along its length (drive bands) as the lands engrave displacing a small percentage of metal. After the boolit travels one "boolit length" down the barrel, the engraving "work" is done and the boolit continues racing down the barrel riding the lands and bore. To me this engraving "work" performed on the boolit consumes a finite amount of energy that is in addition to the acceleration of the boolit mass and friction.

But how much is it? For low to high Bhn's is it a factor? Does it influence the pressure curve?

Another variable is the boolit design and fit. I would think Loverins and LBT designs would have higher engraving forces than a bore-rider. That's not saying the force require to do the initial engraving is a "good" or "bad" thing. I'm just wondering if that first boolit length of travel into the barrel rifling is where accuracy is made or lost in regard to the pressure/acceleration curve.

Nels

[Bass Ackward]

Very interesting read.

One item I have not seen discussed is the influence of the work needed to engrave the boolit into the lands in regards to the pressure/acceleration curve.

The boolit yields permanently along its length (drive bands) as the lands engrave displacing a small percentage of metal. After the boolit travels one "boolit length" down the barrel, the engraving "work" is done and the boolit continues racing down the barrel riding the lands and bore. To me this engraving "work" performed on the boolit consumes a finite amount of energy that is in addition to the acceleration of the boolit mass and friction.

But how much is it? For low to high Bhn's is it a factor? Does it influence the pressure curve?

Another variable is the boolit design and fit. I would think Loverins and LBT designs would have higher engraving forces than a bore-rider. That's not saying the force require to do the initial engraving is a "good" or "bad" thing. I'm just wondering if that first boolit length of travel into the barrel rifling is where accuracy is made or lost in regard to the pressure/acceleration curve.

Nels


Nels,

ABSOLUTELY. If we had a prize, you would win it!!!!

For high velocity bullet design means everything!!! It dictates how hard or how soft you need. That is why I have to in fact go softer sometimes to go faster which is backwards. That's why at times a pistol primer makes all the difference in the world giving the bullet more time at low pressure to over come inertia and engrave and get moving. I use an LBT 150 grain spitze for HV. If that bullet had a narrower front band, I believe I could get more out of it. Because I could go harder.

But guess what? Throat angle also benefits those light 22s that seem to blow up at certain velocities too.

Cast benchresters like long lightly tapered throats and rifling for accurate cast that makes it easier for the bullet to move into the barrel where it will be supported. They know it works, but many don't think about why.

Engraving is just like sizing and it takes time. The steeper the resistance at the beginning whether that be from choking or leade angle or rifling width or bore finish in that throat area, (powder erosion) and soetimes .... hardness makes all the difference in the world. Cause they are affecting the pressure curve. Same as going to a slower twist rate. You cut pressure by changing the angle of the barrier to forward motion. Anything you can do to help a bullet get moving will lower pressure and improve your HV accuracy.

Bullet design is a key and quite honestly, the commercial bullet designs we have were never intended for this purpose. While I like a wide front band for levers and jumping, handguns too in cases, I want a narrower one to allow a softer start. I like 75-80% bearing area to fight the sway of the barrel as the bullet is moving up the whipping barrel. Ever try to walk on a moving bus? This is what a bullet sees going up a bore. And the forces here can size your bullet and cause gas cutting as the barrel changes direction and the force changes to the other side.

Same logic applies with the lightest bullet per caliber that I can reach the lands in my throat. IF I could shoot a 100 grain bullet in a 30-06 I could easily reach 3000 fps accurately. If RPMs were the monster, then the heavier and longer the bullet would give us a longer and stronger bearing area to fight RPMs. And this ain't so either. Think pressure reduction in design for HV.

[Harry O]

One item I have not seen discussed is the influence of the work needed to engrave the boolit into the lands in regards to the pressure/acceleration curve.
Nels

This is an interesting area of engineering. In the distant past (before the widespread use of computers), engineers were only interested in the area of a stress/strain curve below the yield point. They could calculate that. Going above the yield point was a sign of failure. It was also impossible to calculate above that with any kind of accuracy (I could tell you some war stories about that).

Since the widespread introduction of reasonably priced computers and finite element programs, more and more use of the area of the stress/strain curve ABOVE the yield point has been used. For example, the "crush zones" that are mentioned in car ads are places that go above the yield point to absorb crash energy before it reaches the people inside.

You are correct that something similar is happening to the bullet. When the gunpowder is ignited, the pressure goes up. You don't know how quickly because it varies depending on the size of the container. It starts out with a container the size of the inside of the case with the bullet seated. It ends up with a container the size of the inside of the case plus the size of the inside of the barrel. The Powley Computer has you calculate all of that. But it also depends on the steepness of the time/pressure curve or distance/pressure curve.

Anyway, I believe that some of the steepness of the slope of the pressure/time cuve is due to the energy needed to engrave the rifling on the bullet. That slows down the accelleration that the bullet would otherwise have. I believe it also increases the peak pressure. Obviously, if the bullet wasn't rifled, it would be further down the bore, the size of the container would be more, and the pressure would be lower. After the bullet is fully engraved, the forces opposing it would be less and it would pick up speed faster. Unfortunately, by then the powder is pretty much ully burned, so the acceleration drops.

Anything done to reduce the retarding force on the bullet will lessen the steepness of the time/pressure curve and reduce the pressure. That is good for plain base lead bullets. All the things mentioned above will do that.

I once spent some time trying to figure out the acceleration on a bullet. Just taking the speed of the bullet at the muzzle and the length of the bore, you can easily figure a straight line acceleration. You can also figure an acceleration based on the time/pressure diagram. The two figures are widely different. I don't believe either is "correct". There is no steady acceleration with a bullet. It starts out with a relatively slow acceleration, up until about the time the powder is completely burnt, and then slows down from there. Remember that acceleration is NOT the same as speed. Speed picks up throughout the trip through the barrel.

One thing I found interesting is that the place where the time/pressure curve peaks is pretty close to where the bullet becomes fully engraved. They are NOT the same place, but pretty close. There has to be a relation.

[felix]

All what has been said gives great credence for us to obtain take-off BR barrels whenever they become available. These barrels are well broken-in for cast, and a few hundred high antimony, low tin, boolits will smooth out the complete throat (freebore + angle). ... felix

[Bass Ackward]

Harry,

I think another variable for me is the use of full cases of powder. This forces the powder column to ignite from the back and burn forward. This column is following my bullet acting as filler until it burns. I try to make sure I pass the peak pressure before the column burns up.

So we have to introduce case design into this equation. Any case design that encourages powder to burn or to burn inside the case, adds to the problem. Therefore, I want a sloping case with a sloping shoulder that elongates this powder column. As opposed to what we commonly refer to as an "improved" case with straight sides and a sharp shoulder.

The 30-06 would be a superior HV case design compared to a 308 Win of relatively the same volume. You would probably be forced to run a slower powder in a 308 than I do in a 30-06. Same in 35 caliber which is why I shoot a Whelen here.

Again remember here that I am not trying to make a statement on cartridge superiority, only on my thought process toward HV cast.

[Harry O]

Harry,
I think another variable for me is the use of full cases of powder. This forces the powder column to ignite from the back and burn forward. This column is following my bullet acting as filler until it burns.
HV cast.

There are a lot of variables, aren't there. I don't have all the answers, but I know what works for me. Anyone else can try the same thing or do something different. And maybe what they do different works for them. That is why when anyone makes a firm statement and belittles anyone who disagrees is a fool -- at least when it comes to cast bullets.

I spent some time doing R&D for a truck-trailer manufacturer some years back, so I got to see a lot of things that people (including me) thought would work that didn't. They failed under testing. That showed me that theories are nice, but when it comes to what is true or not true can only be decided by CONTROLLED tests. Controlled tests mean varying one and only one variable at a time and testing it. That is what I did when I was experimenting with the 41LC. The downside of that is that I shot something over 5,000 rounds and it took about 5 years to get a pretty good understanding of that particular cartridge. I don't have the time to do that anymore.

BTW, I also found out when I was doing R&D that "data mining" is the most useless method of finding out anything. For example, doing an analysis of what a few champion shooters use is interesting (and which one of our members likes to do all the time), but pretty much useless to the average person. The myriad of details that each of those champions put into their lead mixture, casting, lubing/sizing, loading, and shooting are not known. Not to mention the physical differences from one shooter to another. Only the results are known. All the other reasons that one person wins a match instead of another are ignored. That doesn't work. Controlled testing is the only way to learn more than the most superficial things.

[Larry Gibson]

Bass

"IF I could shoot a 100 grain bullet in a 30-06 I could easily reach 3000 fps accurately. If RPMs were the monster, then the heavier and longer the bullet would give us a longer and stronger bearing area to fight RPMs. And this ain't so either."

What your missing here is your LBT bullet is short and fits the neck length and just enough out of the case to center in the throat and leade. Your LBT bullet has two small lube grooves and a small scrape area in front of the GC. There is no nose to ride the bore and unevenly obturate. The area from the front lube groove to the ogive taper is full diameter (.309") and is about .2" long, essentially a very wide driving band. It is a well designed cast bullet for the '06.

With this bullet and a close fit in your rifle there is very little room for obturation, especially uneven obturation that causes imbalances in the bullet. Thus there is less defects for higher the RPM "monster" to accentuate at higher RPM and adversely effect accuracy with your bullet than say with a 311291. Perhaps the reason your rifle shoots this bullet much more accurately than mine is it simply fits your rifles throat tighter or better than in my rifles throat. You probably have less adverse obturation than I do and thus maintain accuracy at a higher velocity than I do in my rifle. I did get pretty good accuracy at a higher RPM with your bullet but the RPM "monster" did get it way before I reached the velocity you are getting.

Larry Gibson

[felix]

Very true, Harry! Controlled testing by definition requires controlled components. That is very difficult for most of us who like to fabricate stuff out of junk. Junk here means anything that is unknown in terms of quality or quantity at the time of use. I really like the idea of using a stockpile of verified lead/powder/primer/case for repeated performance in the field, but that kills the fun for me because I have been doing that almost all of my professional career. Can't afford a chance. Now for the gun hobby, the excitement of what happens at the target that particular day is more important than knowing the results before leaving the house. ... felix

[Harry O]

Very true, Harry! Controlled testing by definition requires controlled components. That is very difficult for most of us who like to fabricate stuff out of junk.
felix

I do very little casting with WW. I probably have less than 100 lbs of it. I have about 1,200 lbs of roofing lead that I bought at the same time from a local recycling place (back when it was 22 cents a pound). It took three trips with my car to get it home. I tested it with three different hardness testers and tested quite a few of the ingots from start to finish while reducing it to ingots. It seems to be as pure as you will ordinarily get with lead (Bhn 5). In addition, I have about 350 lbs of monotype (with material certification) which was also bought at the same time and the same place. Finally, I have a bunch of pure tin.

I can, and do, mix up exactly the mixture I want for different bullets, bore sizes, and loads. I worked up a chart for figuring out in advance what I need for the Bhn I want (a link was posted here once before). It has proved out to be pretty darned close after several years of use.

Of course, the cooling rate of the bullet changes that a little. I remember casting three different bullets from the same mixture at the same sitting. One was about 100gr, one about 185gr and one about 270 gr. All were air dropped into a folded towel. The 100gr was about half a Bhn harder than the 185gr, which was in turn about a half Bhn harder than the 270gr. The middle size was about what I predicted for the Bhn.

[felix]

Harry, you are well qualified to be a boni-fide tester. You got the components and tools to do a bang-up job. ... felix

[leftiye]

Nelsdou,
I've been thinking about that same issue, the difference between acceleration down the bore versus the effects of pressure while getting started against the resistance of the leade. I think that in the first instance the pressure pushes against a piece of lead that is for all intents not just stationary (inertia), but trapped in place by an obstacle. At this point pressure that will deform is BHNX1400. (So keep your initial pressure low), plus in the case of the starts of the lands the area absorbing the force is small and pressure multiplies there

Later while traveling down the bore the rate of acceleration has to be high enough (we CAN calculate this rate for each hardness of lead) that the combination of the pressure on the base (probably greater than 1400XBHN) against the inertia of the frontal parts of the boolits exceeds 1400XBHN for the midsection of the boolit before deformatin can occur. Because the boolit is trapped in the walls of the bore, and lube is relatively incompressable, you may be able to exceed the 1400XBHN for the given alloy maybe even quite a bit before deformation that destroys accuracy occurs.

Harry,
would you rather get hit by a hammer, or the same mass of water in a balloon (at equal speeds)? Just like a Karate fist, the hammer concentrates the area of the force multiplying many times the PRESSURE of impact. Plus, there is no compensation within the hard mass, nothing upsets reduceing the TIME that the impact takes to transfer energy. On the other hand, a water balloon spreads out the impact and pressure becomes equal at all points on the surface impacted.

[fecmech]

Gentlemen--I'm a pistolero who is very happy with 2"@ 50yds with his handguns and next to no cast rifle experience. That said I've been following these 2 threads with great interest. Could freebore in rifles aid in that critical initial acceleration for higher velocity cast??

[felix]

Cast custom BR guns have a small amount of intentional freebore to help hold the boolits straight during that most important phase of ignition. The downside? The throat wears out quickly, forcing the user to seat less deeply as time goes on. Critical loads have to be adjusted to maintain accuracy. When that fails, it's time for a re-chamber, and a re-crown if necessary. Freebore for ignition purposes only? Probably not if the case capacity is half way reasonable for the mid-speed powders where there are many to be found to make things happen. ... felix

[Bass Ackward]

Gentlemen--I'm a pistolero who is very happy with 2"@ 50yds with his handguns and next to no cast rifle experience. That said I've been following these 2 threads with great interest. Could freebore in rifles aid in that critical initial acceleration for higher velocity cast??


Fecmech,

Maybe. I couldn't tell you. What I do know is that I need that contact with the rifling for three reasons. First is to maintain headspace. Slow powder loads don't maintain headspace very well. seating into the lands does this. It also performs a centering without having to choice the throat. I want to stay closer to bore size in this case. Third, it does aid ignition with the slow powders I am using.

So while a free bore may aid inertia, it wouldn't do much for ignition or my headspace. And if I had to go to a faster powder, I think the benefit would be negated.


Larry,

I did not mean to mislead anyone. I did not say that that bullet was poorly designed. I just said that for my needs, it could be better.

Veral told me himself that he made that bullet for a guy back in the late 70s that wanted a low velocity target bullet. That bullet was supposed to weigh 160 grains. But because the use was intended to be low velocity, the GC shank was shortened to almost have no space for lube.

This is counter to Veral's normal HV designs where the GC groove is wide. Veral believes that gets the lead away from the obturating pressure. Veral bet me I would never get anything over 2000 fps with that bullet, and was flabbergasted when I pulled it off. He IS right though about the wider GC groove if it doesn't destroy balance.

If you get one of those, I suggest you buy the stock mold which will be a better HV design even though the weight is a little heavier. Anyway, we will get you there one day. :grin:

[Larry Gibson]

Bass

I know you didn't denegrate the LBT design. I only meant the comment as a compliment. I do think it is a good design and as you've said, perhaps could be a little better. I think it leaves little room for unwanted obturation in the '06 as is though.

Larry Gibson

[Nelsdou44]

With all that's been said about the pressure curve after ignition, deformation of the boolit base, etc., then what is it about paper-patched boolits that allows comparable accuracy at higher velocities?

For example (my experience anyway) similar alloys, one boolit (sized to bore or slightly over) and PP'd will shoot well over a full power load of medium speed (3031) powder compared to another boolit (sized to fit to slightly over groove diameter), lubed, and CG'd, same load.

The bases of the boolits see the same pressure/acceleration curve. Or do they? I always thought the paper kept the lead off the steel, preventing stripping of the rifling. Or does the paper help the boolit to engrave into the lands quicker with less distortion and thus a truer launch?

Nels

[Harry O]

Nelsdou,
Harry,
would you rather get hit by a hammer, or the same mass of water in a balloon (at equal speeds)? Just like a Karate fist, the hammer concentrates the area of the force multiplying many times the PRESSURE of impact. Plus, there is no compensation within the hard mass, nothing upsets reduceing the TIME that the impact takes to transfer energy. On the other hand, a water balloon spreads out the impact and pressure becomes equal at all points on the surface impacted.

The only difference between a hammer and a water ballon is the slope of the pressure rise curve. With a hammer it is vertical. Pressure rise is instantaneous. That is where we get "impact loading". With BP, it is sloped slightly. That means that the pressure rise is NOT instantaneous -- it takes just a little time, so the blow is cushioned ever so slightly. With Bullseye, it is sloped more -- more cushion. With 4227, it is sloped even more. With a water ballon, it would be laying down almost flat. No, they are not the same, but pressure is pressure. It can all be calculated.

[Harry O]

With all that's been said about the pressure curve after ignition, deformation of the boolit base, etc., then what is it about paper-patched boolits that allows comparable accuracy at higher velocities?
Nels


I think this has been answered here, although I have absolutely no experience with paper patched bullets.

I would be willing to bet that the force it takes to engrave a PP bullet with rifling is a whole lot less than the force it takes to engrave a lead alloy bullet. That means that the velocity will be higher for the same pressure. There is less resistance to the bullet when it first starts out. You will not be putting MORE pressure in the base of the bullet. If anything, you will be putting less pressure on the base with PP.

[Bass Ackward]

With all that's been said about the pressure curve after ignition, deformation of the boolit base, etc., then what is it about paper-patched boolits that allows comparable accuracy at higher velocities?

For example (my experience anyway) similar alloys, one boolit (sized to bore or slightly over) and PP'd will shoot well over a full power load of medium speed (3031) powder compared to another boolit (sized to fit to slightly over groove diameter), lubed, and CG'd, same load.

The bases of the boolits see the same pressure/acceleration curve. Or do they? I always thought the paper kept the lead off the steel, preventing stripping of the rifling. Or does the paper help the boolit to engrave into the lands quicker with less distortion and thus a truer launch?

Nels


Nels,

I sort of agree with Harry, how can we know without test equipment? But the one thing you can be sure of. No matter what material you put in a bore, it feels the pressure. Copper feels the same pressure, the only exception that when it begins obturation at about 34,000 psi, it doesn't require a lube or paper to continue unless you outstrip the protective covering of the copper and tear up the bullet.

I am not a paper patcher either. Poor patience, and arthritis make me look at other alternatives. But that paper patch is going to feel that same pressure as lead because the core IS lead.

And the RPM forces are just as great on the paper as on the lead. And we all know paper is stronger than lead against RPMs, right? :grin: SO paper overcomes RPMs. :grin:

So for me the only variable that you are removing are the galling from forces that the lube is protecting the bullet by lubrication from pressure. When pressure overcomes the material, and or lube you are using, you / accuracy fails. Be that lead, copper or I would guess that ultra strong RPM fighting paper. (did I over do that point? :grin: )

[Larry Gibson]

"Or does the paper help the boolit to engrave into the lands quicker with less distortion and thus a truer launch?"

Back in my PPing days that was my thought. A true PP bullet has very shallow grooves, if any, and is not distorted by the rifling. The distortion of a cast bullet by the rifling creates defects in the balance of the bullet. Those defects in balance are what is accentuated by RPM at a certain level accuracy is lost. Also with the very small grooves on a PP bullet there is little room for set back obturation. The PP bullet is, in effect, a stronger bullet able to with stand more accelleration before unwanted setback creating defects that upset the balance of the bullet occurs. The bullet is able to with stand accelleration better because it is supported more by the PPing in the throat and barrel. By sizing down your bullets you in effect swaged out some defects and minimalized the size of the grease grooves. That along with no defects from rifle engaving minimises the defects in the swaged down PP'd bullet. Thus accuracy was maintained at higher RPM with the PP'd bullet vs the regular cast bullet because there weren't the defects in the PP'd bullet caused by eneven obturation and rifling for RPM to accentuate. The more balanced the cast bullet (PP'd or regular cast) on exit from the muzzle the more accurate it will be, particularly at higher velocity/RPM.

As example I found that the Lovern 311466 when sized down to .301 and PP'd shot every bit as well with the same loads as the designed for PPing 301618. Bullets were cast of the same alloy (50% WW - 50% linotype). The loads were developed for a friends Target M70 in 30-06. The load was with IMR4350 and velocity was in the mid 2600 fps range. I'm working off memory here as the 301618 and 311466 moulds were his as was all the loading and sizing dies and the data stayed with him. I did cast up about a thousand 311466s using his mould and sized them in his .301 die, PP'd them and used them in a M1903 over 45 gr of IMR4895. Velocity was 2594 fps at 186,842 RPM with a consistant 3 MOA grouping at 200 yards (my eyes were a lot younger then and I could use the issue aperture sight quite well). I also had some of the 311466s that I sized at .311 and lubed and shot in that rifle as regular cast bullets. I lost 2 MOA accuracy at 100 yards with both 4895 and 4350 right at 2,000 fps and 144,057 RPM.

I've recently picked up a 311466 mold and will probably try PPing again.

Larry Gibson

[leftiye]

Everyone's got good perspective on the Paper patch thing. I like Harry O's approach especially. One can see how this (lowering the force of engraving) would lower initial pressures, and secure all of the benefits that entails, Including less deformation and lowering initial pressures, and delaying the pressure rise and peak.

[Bass Ackward]

Here is an example where I used bullet design to cut pressure while still maintaining alignment. I bit my tongue here and designed a short bore ride section. This gives the alignment I need with the bullet able to move 1/8" before the front band makes contact. This is a fairly new winter design for me that I tried this morning since we got down to 20 degrees. Rifle and ammo was left out all night. The bore ride makes a sharp shoulder to deal with the lube (fouling) in the bore.

The load is 46 grains of RL15 with a Remington rifle primer and my 255 grain bullet. Velocity was 2163 av with an ES of 31. This barrel was clean so the first shot was blown in the dirt, here are the other 19. The 10 on the left with the black dots under orange were sized .3585 and the other 9 were .3595. Looks like I could go maybe another 1/2 to 1 grain higher with this one.

Pat, here is an example of a rifle that sucks with low velocity cast. But it does fairly well at higher velocities. You wanted group sizes and pictures. :grin:

http://i146.photobucket.com/albums/r267/ba2_shoot/35255.jpg

[Larry Gibson]

Bass

Nice shooting loads in the .358 (assuming 100 yards). If that's a 12" twist barrel that load is cranking 129,780 RPM, or a 14" twist they're at 111,303 RPM, or a 16" twist they're at 97,359 RPM. Which ever twist your rifle is that load is well within the RPM threshold and the groups show it. Pretty much the same with my Shilen 26" barrel on the M91 Argie with 14" twist chambered in .35 Remington. I can shoot the 200 gr RSBS cast bullet to max velocity given the case capacity and still be within the RPM threshold.

Larry Gibson

[KYCaster]

So, Bass....quit teasing us and tell us about the boolit. Weight?...Length?...Nose shape?....Pix would be nice.:roll:

Jerry

[Bass Ackward]

Bass

Nice shooting loads in the .358 (assuming 100 yards). If that's a 12" twist barrel that load is cranking 129,780 RPM, or a 14" twist they're at 111,303 RPM, or a 16" twist they're at 97,359 RPM. Which ever twist your rifle is that load is well within the RPM threshold and the groups show it. Pretty much the same with my Shilen 26" barrel on the M91 Argie with 14" twist chambered in .35 Remington. I can shoot the 200 gr RSBS cast bullet to max velocity given the case capacity and still be within the RPM threshold.

Larry Gibson


Larry,

Really? See that barrier thingy never enters my mind. Load and go baby. Wonder what I can do if I harden these? Oh yea, 100 yards. This is the most .... consistant in the cold that I have ever done.


Jerry,

Nothing special here. I tried 3 pictures of the bullet and they are just too blurry. I can do up a page and fax it to you if you want to use the PM feature.

[Pat I.]

Pat, here is an example of a rifle that sucks with low velocity cast. But it does fairly well at higher velocities. You wanted group sizes and pictures. :grin:

Bass,

Excellent shooting. What gun are you using?

Pat

[Bass Ackward]

Bass,

Excellent shooting. What gun are you using?

Pat


Pat,

Sorry. Most of the folks around here already know, it's a 35 Whelen sporter built on a Savage 110 action with a Shilen barrel.

[Pat I.]

Pretty neat. When I was first thinking about getting into BR shooting and not knowing if I'd like it or not I built my first gun on a Savage SS action using a 30 cal Shilen 14 twist SM barrel . I had an 06 reamer so cut an FL 06 die down and formed some brass out of 35 Remington til it looked about right and chambered it up. I got the idea for the case out of a FS article about a guy that turned a Marlin 336 into a single shot off hand rifle. The thing shot pretty good and gave me a good education since this was my second attempt at fitting a barrel. I think this was one of those times where not knowing my limitations worked out.

Savage was just getting back in the game at the time so what they considered a varmint rifle at the time consisted of a long actioned SS with a skinny cheap plastic stock so I got a 3z3 piece of oak from Gun Parts and notched it out so it'd fit over the fore end and glued it on. The thing was ugly as hell but it shot pretty good.

[Bass Ackward]

The thing shot pretty good and gave me a good education since this was my second attempt at fitting a barrel. I think this was one of those times where not knowing my limitations worked out.


Pat,

Interesting. Did you name it?

All joking aside, just like Larry said, you might be surprised what that plain old 35 Remington will do as a cast bullet gun for bench or hunting with say the RCBS 200 in a throat cut to fit it.

This Whelen is in a plywood stock and bead blasted. So homely, many people believe it is a factory Savage until I show'em different .... for a slight fee. :grin:

[Pat I.]

Pat,

Interesting. Did you name it?



If I remember right I used to call it the 30/35 or something like that on the tech sheet but whatever I called it would be in one of the older FS because I used it in competition. I think what was much more interesting about the case was how the guy made the 336 offhand rifle for it, a good read if you can find the issue.

Pat

[Bass Ackward]

I thought I was done with this but decided to report it anyway as food for thought.

I went back today and tried shooting some of the same bullets that you see from the targets above, only this time I water dropped them. These bullets were 20 BHN. That is 6 BHN more than last weeks bullets. Last weeks test showed almost no difference in group size between .3595 and .3585. Remember, bore is .3582 and the throat is .360.

This week, the 20 BHN bullets that were sized .3595 started at 2" and went to 4" groups with the same charge as last week. Now before you say I told you so, the .3585 accuracy bailed me out and came back at an average for the 3 targets of .823. Last week's average was .849 for both sizes.

That is exactly .026 difference from last weeks groups. What is surprising to me is the increased sensitivity to sizing that came from just 6 BHN. And pressure failure looks suspiciously like RPM failure. That's how critical pressure with cast can be.

[Pat I.]

Bass,

Just out of curiousity what twist are you running and how are you testing pressure? Groups opening from 1 inch to 4 inches because of a 6 BNH harder bullet seems extreme and I wonder if the gun would even notice it especially with the load you're using which wouldn't be considered a hot load in the Whelen.

Pat

[felix]

It's true, Pat. Shooting wadcutters at various lengths, diameters, hardness, with various pressure curves will drive that boolit destruction idea home. There are very few boolits worth looking at down range because of the various states of non-uniformity among them. I'd say only about 50 boolits out of a 1000 show what we are looking for. Many of them get destroyed by being shot into the lands on a cock-eyed basis which makes those boolits worthless for analysis. Patience is really required over the long haul towards any kind of "proof" of what we are looking for. ... felix

[Bass Ackward]

Bass,

Just out of curiousity what twist are you running and how are you testing pressure? Groups opening from 1 inch to 4 inches because of a 6 BNH harder bullet seems extreme and I wonder if the gun would even notice it especially with the load you're using which wouldn't be considered a hot load in the Whelen.

Pat


Pat,

14 twist. Pressure is predicted by Quickload. If the velocity chronographed matches with the computer prediction, then I assume pressure is fairly close. (Velocity is proportional to pressure)

Velocity with the larger diameter, 20 BHN bullets was about 60 fps higher than last weeks velocity. This is almost 150 fps higher than Quickload predicts with a Shot Start Pressure of 1160 for lead. If I raise the SSP to match velocity, we are almost to jacketed resistance levels at .0015 over bore for this powder speed. Remember, this doesn't materially alter the over all pressure, but it does dramatically affect the acceleration and pressure curves which were enough to show a material change. With the material change enough to deform my bullets apparently. POI was about 1 inch higher on target too.

If I have time before season, I will see just how much lower in powder charge I would need to go with RL15 to bring it back in at that hardness. But my guess, is I would have to drop down in burn rate speed to say 4350 to achieve a flatening of the pressure curve to where diameter wasn't so finicky. (for this gun)

[Pat I.]

Bass,

Since pressure equals velocity and velocity equals rpm at the moment we're not really sure if it's a pressure isue or a rpm issue. I'm also not quite sure a .0015 over 20 bnh bullet will equal the shot start pressure of an equal weight jacketed bullet. Don't know what parameters Quickload uses but I have my doubts.

[Bass Ackward]

Bass,

Since pressure equals velocity and velocity equals rpm at the moment we're not really sure if it's a pressure isue or a rpm issue. I'm also not quite sure a .0015 over 20 bnh bullet will equal the shot start pressure of an equal weight jacketed bullet. Don't know what parameters Quickload uses but I have my doubts.


Pat,

Can't possibly RPMs if .3585 brings it back in. Has to be pressure or .... harmonics from more friction.

[Pat I.]

Sorry John that was my mistake. I thought you said only the bigger bullet was faster but rereading set me straight. It doesn't matter anyway because it's all theory and unless I have a specific need for velocity or to prove something to myself, which I'll gain by using a slower twist, it's not that important to me. I don't hunt but if I did it would be with my 1895 or 1894 with a heavy bullet with a big meplat at around 1700 fps which is easily attained.

Take Care,
Pat

[Bass Ackward]

Sorry John that was my mistake. I thought you said only the bigger bullet was faster but rereading set me straight. It doesn't matter anyway because it's all theory and unless I have a specific need for velocity or to prove something to myself, which I'll gain by using a slower twist, it's not that important to me. I don't hunt but if I did it would be with my 1895 or 1894 with a heavy bullet with a big meplat at around 1700 fps which is easily attained.

Take Care,
Pat


Pat,

Please DO NOT look at this as that I am telling you, "this is how to do it". Just think about it.

We, as casters, seem to believe that it is always preferable to .... choke. I have just demonstrated an exception to this.

In this case, I would bet that RL15 or 4320 is my cut off with this weight bullet in this gun and all powders above that point would increase diameter sensitivity. And the result most guys would say is failure of lead to handle RPMs.

So how many RPM believers simply run a single diameter test and then see resulting groups when they try higher pressure loads and then blame RPMs? This was a great test because as Larry pointed out, RPMs never enter the picture with this bore diameter. I had good accuracy not apparently at any RPM barrier, lost it from a hardness increase, and got it back by sizing smaller.

This is what I see all the time. In handguns, one guy will say that a particular bullet design wont shoot in his gun. The correct statement to make is that it won't shoot in his gun the way he is reloading it and the things he is subjecting it too. The options are to learn how to make it work or change designs.

Back to rifles, the faster the twist, the larger the case capacity needed to minimize pressure and this RPM barrier moves higher. And if you have more case capacity, a longer barrel helps to burn it. Or the lighter the bullet. Or the slower the powder if you can still burn it and get higher velocity. At some point you pass the peak and slower powder burns, but a lower velocity is obtained.

But every ..... single .... time I reach an .... "RPM barrier", if I treat it as a pressure problem, and take steps to cut pressure, I can go on up in velocity. This was a good example where RPMs didn't affect softer bullets, so pressure or harmonics was the only possible reason. And another law that was broken is that you need harder bullets to go faster. And harder bullets are always more accurate. There are no laws in shooting cast.

[Larry Gibson]

Bass

I believe you're tracking but I have one point; I give RPM a "threshold", not a "barrier". That threshold is several thousand (near as I can tell so far around 15,000) RPM. The reason is that for the RPM to adversly effect accuracy the bullet must be imbalanced. This can be through casting defects, excessive obturation, the bullet breaking apart or misfit of the bullet in the throat or bore. All cast bullets will have some unbalance when they are fired do to one or more of those reasons. It is somewhere within the RPM threshold that accuracy will decrease because of the effect the RPM has on those defects. For example; The slower we accelerate the bullet the less obturation. Thus (assuming quality cast bullets that fit the throat) if we use a medium burning powder we may loose accuracy early in the RPM threshold but if we use a slow burning powder to lesson the time pressure curve we may be able to push the bullet to the upper limits of the RPM threshold before losing accuracy. This because the slower acceleration of the bullet by the slower burning powder did not obturate the bullet as severely so it to a higher RPM to accentuate those defects resulting in lost accuracy.

In the case of your harder bullets I'd suspect the larger diameter hardened bullet may be being damaged by swaging to fit the bore during accelleration. Years past I had shot some .30 cal cast bullets that were cast of linotype and were inaccurate. As the bullet had a scraper groove in front of the driving band I suspected the long nose was bending to one side as it was a poor fit in the bore. I was pushing them at 2100 fps out of a 10" twist '06. Accuracy with the same bullet cast of WWs, while still not good, was better than those cast of linotype. This just did not seem to jive with the then current thoughts of shooting cast bullets, i.e. harder bullets should be more accurate. I had access to a bullet catcher at the crime lab so I shot 5 bullets of each into it. What I found was with the harder linotype bullets the nose did not bend to one side but chunks of the bands had broken off where the rifling rode over them between the driving band and the GC. On most of these bullets the chunks broke off on one side. This created a really unbalanced bullet which will yaw and pitch at any RPM. The nose of the WW bullets had set back collapsing the scraper groove and was crooked as it was engraved on one side of the nose. It was however not as unbalanced as the harder bullets with chunks missing from the side.

I guess my point here is that your hardened oversized bullets may be being damaged and unbalanced more than we think. Then any RPM is going to cause inaccuracy. Your loads at 2160 fps or so out of the 14" twist barrel are below the normal RPM threshold. I suspect, as you do, that the time pressure curve is steeper with those loads because of the harder oversize bullets and more damage to the bullet is occuring during acceleration.

Larry Gibson

[felix]

If a boolit is obturated too far before it is fully supported by the barrel, the boolit will definitely have severe rotational problems outside of the barrel. That "too far" will not be too far when the boolit is augmented with tin to make it tougher. Lino, cut in half with something like WW, and then a little tin added, will make the boolit have a much better rubber band effect. If the internal binders within the boolit are weakened or destroyed, meaning the rubber band was stretched too far, then the booit will rotate itself off of the target quite easily. It is too bad copper is so hard to inject into the mix in a proportion to keep boolits uniform because that element has shown to be the all time superior boolit toughener in my experience. ... felix

[Bass Ackward]

Thanks guys. I just wanted to get some thought going as " I " was clearly unprepared for that much change as was observed from such a slight hardness increase. I watter drop a lot of 30s and 44s/5s all the time, but seldom HT any 35s unless I was trying the 50/50, WW/pure. In fact, I have never observed anything as radical with the larger bores, but 30s show some of the same tendencies. Now that I think about it, with the numbers I got at 20 BHN, I think I got my batches mixed up and did use the 50/50 WW / pure. But 20 BHN is still 6 BHN harder than 14 and still caused the problems that were fixed by sizing even if I did screw up.

You can imagine, here I was thinking to myself, thank God Larry wasn't here (:grin:) to tell me I told you so as this gun has NEVER shot over a 2" group with bullets of any kind that I can remember. I was kinda low till the .3585s came back in with the same charge.

I was expecting to have to go on up in powder charge with both and this was just a size test. You know what my next test is without me telling you don't you? Out comes my .357 sizer and we'll see what shakes out there. There was a fella awhile ago that posted he was sizing at .356 and doing well, but I never got around to asking him what his bore diameter was.

Felix,

You are right about the copper. I get it in Babbitt.


Larry,

I am not trying to say that there isn't ever a case that RPMs don't flub ya as I always say, avoid the word always with cast. But I will at least say pressure exhibits the same signs on the target, so it pays to treat the pressure first and see if things come round.

If I really wanted top velocity with a 250 grain bullet in a 35, I would build a 358 Norma with a 26" tube. Then I ought to be able to get 2400 fps with ACWW using a 14 or even a 15 twist. Cut a short enough throat for a 200 grain and you could get 2700 fps with it no matter what the RPMs are. But 2100 just works dandy here on my deer and I guess is good enough.