Do you believe that lead boolits actually obturate (swell up) when fired? Yes or No

[Molly]

Hi StarMetal,

> I don't tag along with your leading theory. Leading can and does occur due to high stresses of the bullet sliding against the bore because [COLOR=Blue]of lack of lubricant and in some instances a rough bore. [COLOR=Black]

So I was told as a youngster, but decades of intense interest and experiments has yet to dislodge the first evidence of it being a real failure mechanism. While rough steel will indeed abraid alloy from a cast bullet, it simply lies there: There is no trace of adhesion of the abraded lead to the steel. You can simply wipe it off with your fingertip. If you don't believe this, it's easy to test. Get a piece of mild steel and roughen it with sandpaper, sandblast or whatever strikes your fancy. Then get a hard cast bullet and start scrubbing. You'll half wear out the bulllet without seeing any adhesion. At least I did when I tried it.

>Try shooting a non lubricated cast bullet void of any oils or dry lubes and tell us what happens.

As for lack of lube, it so happens that I can indeed fire a dry, hard cast bullet in a dry bore without leading. And the bullets are also both unsized and without a gas check. The only difference between the bullet so loaded and fired and one just cast is the temperature of the bullet. I've done it many, many times, with loads up to and including Hornady handbook jacketed maximums for the round involved. Accuracy varies from fair to good. Seldom match grade, but plenty good enough for hunting. What's more, I can fire many such rounds without cleaning, and when I'm done, the bore is lead free, and as clean and bright as if it were just cleaned. How? Just add some Cream of Wheat or corn meal below the bullet. That's all. The amounts to add, and other details have been published many times.

>Explain why, with jacketed bullets, there are jacket deposits along the whole length of the bore.

I really can't explain the discrepency, and I know you are right about jacketed fouling. But I think I can give you a reasonable speculation, that the surface tension of lead is probably higher than that of copper. Surface tension is a property of all materials, and it defines the ability of one material to wet and cling to another. The lower surface tension material will invariably wet the higher surface tension material. This is why you add detergent (with very low surface tension) to water (which has a pretty high surface tension) to improve its ability to wash your dishes or clothes. I notice that most popular bullet lubes are organics (like wax or grease) with low surface tension. I suspect that one function of lubes is to contaminate the bore to make it harder for the molten lead alloy to wet it out and adhere. I speculated on this during a correspondence with Col. Harrison (the NRA cast bullet expert that devloped Alox lubes) and he said that he thought I might be right.

>I'd say the reason leading is more evident near the breech end is because that's were the bore is the most rough due to erosion in addition to high temperatures because of the powder burning which add to the stresses of the bullet sliding along...in other words making it easier for the lead alloy to gall off onto the bore.

That's logical, and it would make a good theory except for the fact that leading free loads can be assembled for the roughest pitted, rusted and eroded bore. Granted, they might be light loads, but the bore roughness and abrasiveness is still the same nonetheless. If galling of lead from the bullet surface really contributed to leading, then any rough bore should lead like mad with any load that puts the bullet out of the barrel. This is easily demonstrated to be incorrect. Try the abrasion test I described above, and I believe you will change your opinion on this matter.

>I also believe that air rifle pellets are lubed.

Yes, some of them are given a dusting of graphite or some similar dry lube, which gives them a darkened appearance. But again, many of them are obviously clean bare lead. I refer you to the Sheridan 5mm air rifle pellets, which come to mind as examples. I have a Sheridan Blue Streak that has seem sporadic but fairly extensive use over about four decades, and has yet to exhibit the first trace of adherent leading. I also own a fair number of other air rifles, and they are invariably free of leading.

>Be nice if you could use compressed air to drive a 30 caliber non lubed bullet out of a rifle barrel at gun powder velocities and not get any leading. That would be an eye opener in the leading question.

Actually, it isn't too hard to come up with an example very similar to what you describe. Air rifles are not limited to very small calibers. A very few minutes on the internet will yield high power air rifles that are used quite successfully for deer and other big game hunting. Their bullets? A home cast round ball is quite commonly used to feed such guns, but some of them are designed to use elongated lead bullets normally sold for gunpowder arms.

>Next you'll be telling us that chalk marks the slate on the blackboard because it's melting.

Nope. But you'll have to conceed that the chalk on a blackboard doesn't even begin to exhibit the adhesion that characterizes firearms leading. You can wipe it off with a cloth (or an eraser). And anyone who's ever dealt with a case of firearms leading will have no trouble telling you that the one is a far cry from the other.

You can file or abrade lead to get it into a dust-like form, and sprinkle it on a piece of clean steel. And you can also wipe it off with a rag or your finger. Like chalk, it will have no adhesion. But sprinkle a little more of that lead dust on the clean steel and set it on your stove until the lead dust melts. If you let it cool, it'll take a hammer and chisel to get the soldered mess off.

[StarMetal]

Molly,

I'm aware of the new age modern air rifles, but I'm talking about propelling say 180 grain cast 30 caliber bullet from a rifle barrel of about 24 inches to the velocity of say around 2600 fps or more unlubed. I'd like to see the bore after say 200 rounds.

I believe the surface tension of metals are in their liquid state. That wouldn't apply to what we are discussing. Maybe your were thinking of coefficient of friction such as in static and sliding.

[Multigunner]

Hi Multigunner,

>Well Molly the reasons why conclusions on the mechanism by which the lubricated match bullets caused action failures of the Springfields aren't quite the same as those in which grease caused only a slight increase in velocity and noticable rise in pressure of the .303 are because the design philosophy and stage of development, plus the maximum chamber pressures of these cartridges and their platforms are far more different than you might think. Remember that the Lee Enfields were built to far looser tolerances and the chamber pressures were far lower. The throat of the Springfield was a tighter fit and bullets were a close match to bore size. The pressure curve of the propelants was also different.

You make some valid points, but (If I recall correctly) Hatcher's Notebook attributed it to grease incompressability preventing normal expansion of the neck and thus normal release of the bullet. When the practice was forbidden, the cracked and broken Springfields also went away. Me? "All I know is mostly from what I read." (Will Rogers, possibly paraphrased)

Well you can check pages 94 0n to about 98 in Reynolds Lee Enfield and see that besides differences in cartridge and propellant the lubricants tested were also very different, and differences in result were noted when the clearance in throat or leade were greater.
The standard British "Rangoon Oil" was tested both freshly applied and after the surface dried to leave a protective coating, and Mineral Jelly was tested applied to different points of the bore and chamber.
The Mobillube fiasco that later damaged Springfields involved a very different class of grease with very different properties.

>As for Mann's conclusions, I found a PDF of his work and his reasoning is very straight forwards and easily understood. Perhaps you should read it again.

Perhaps I should. Refreshment is always a good thing. But my copy (along with nearly all my books) are packed away in storage, awaiting movement to a new home. But I don't think I mis-remember his conclusion that the throat pressure is high enough to expand bullet bases, and must invariably do so. If so, his explanation doesn't account for the fact that every single bullet he fired from that progressively shortened barrel had to be upset to fill the bore. But he got good accuracy from the long barrel, and horrible accuracy and upet from the shortened testing.

Because that shortened barrel allowed enough muzzle blast to mushroom the base of the fired bullets.
His conclusion on the upsetting in the throat was based on both extrapolation of the effect of pressures at various points in bullet travel and the concave appearance of the bullet bases of those fired from a barrel of normal length.

The experiment with shortened barrel proved sufficient pressure and acceleration forces remained to continue the upsetting action for a good way up the bore, which is why such continued acceleration can force a bullet to conform to bulged or eroded portions of the bore in the first few inches of travel, but that force drops off as the bullet reached its limit of velocity as it neared the muzzle of a full length barrel. Some pressure remained but not enough to give a sufficient G force of acceleration.

Seems to me that if the throat expansion is a constant, and results change, you need to look at what else changed. In this case, muzzle blast. I have other results that suggest rather strongly that muzzle blast is a primary failure mechanism of cast bullets. It is possible to take Lyman reloading data for a given bullet and maximum powder load, and calculate a relative muzzle pressure based on the ideal gas laws. .

Had to shorten the post a bit

If the bullet base is deformed by muzzle blast inaccuracy is the result, just as it would be if the bullet base were deformed by any other means before loading.
Gas checks reduce such damage and allow stronger charges. Card over charge wads also acted to reduce damage to bullet bases and reduce blowby.
Without its over the charge wad the MkVII .303 burned out barrels in less than 2,000 rounds, with the card average bore life was 12,000 rounds.
Card wads were common with heavily charged BP cartridges and Express cartridges.

But Mann, to the best of my recollection, did not consider muzzle blast among the factors he tested.

You should look over those photos again. Also remember that actual target rifles of his day had very long barrels and minimal muzzle blast, and residual pressures after exit of the bullet were a great deal lower than with smokeless powders of similar energy. BP muzzle blasts are impressive, but thats due to the mass of ejecta not pressure or heat, which is a fraction of that of even mild smokeless powders.

If so, then his results and mine are different, as are our conclucions. I find that WITH HARD CAST BULLETS, no evidence of base upset is observable on recovered bullets: The gas check shanks do not exhibit the bore-filling expansion of .22 bullets, the grease grooves are not shortened or expanded, etc.

From what you've said you use very light loads and your group sizes indicate that you might get better accuracy with either a slight increase in the load or a slightly softer bullet. BP target rifles in a similar velocity class printed far tighter groups than you find acceptable. One holer ten shot groups at 200 yards were not uncommon for the .32-40 target rifles of Harry Pope for one example and this without a gas check and only a thin over charge card wad. Those rifles generally used a false muzzle and a sealed blank charge rather than loading as a normal breech loader of course.

>Now as for a bullet of .312 in a .308 bore, its likely that bumping up would have little benefit other than to insure that the bullet did not skid in the rifling allowing gas to leak past the corners of the portion of the surface in the grooves.

>Instances of skidding and its effects can be illustrated by the example of a .22 bullet known to have been fired from a certain rifle not being matched to the rifle by foresic examination. In that instance excessive grease in the bore coupled with the low pressure of the cartridge allowed the copper washed bullet to skid leaving the engraving of the lands far wider than normal, a lead bullet fired in the same barrel without grease filled out the grooves and prevented skidding.

We do disagree rather sharply here. I think I have seen and reproduced what you refer to as skidding, though I refer to it as engraving enlargement. In my tests, it began to occur when etching of the gas check shank had formed a complete or nearly complete encirclement of the gas check shank. The amount and type of lube was a constant. As the power of the load increased, bullets recovered with no or minimal etching also exhibited land engraving that was equal in width to the bore lands that produced them. However, as the power of the load increased, the width of the land engraving began to increase. Gas etching naturally began to be visible in the enlarged lands, first in the base band, and then progressing forward on the body of the bullet as the load was increased. This gas blowby etching was very obviously far worse or more extensive on the side of the land that did not force rotation of the bullet: IE, gas etching didn't occur on the side of the land that was pressed tightly against the body of the bullet. I also noted that when loads were too powerful for good accuracy, leading would flash at the muzzle from the trailing edges of lands, obviously from gas blowby from enlargement of the land engraving.

Beyond the pressure levels that produced this, shooting was wild, and I was not able to recover sample bullets for examination. However, a speculation that higher loads continued to produce greater land enlargement until it merged with the neighboring land to produce a smooth bullet of substantially bore diameter seems reasonable, which would account for the complete loss of accuracy.

Sounds like you had a very oversized throat or undersized bullet to begin with to allow that much blowby, a too hard alloy would contribute.
The skidding of that .22 bullet due to grease in the bore was a finding of forensic science, and cited in the literature. One causation does not not cancel out another causation.
Your instance of blowby damage confirms my previous examples of blowby damage when bullets do not bump up to seal properly. Without a proper bullet to bore seal things begin to go wrong quickly.

>When the first Short Magazine Lee Enfields were produced they used the same MkVI cartridge as the earlier Lee Enfields, to maintain the same muzzle velocity from the 25 inch barrel of the SMLE MkI as from the LE rifle with its much longer barrel , the last fourteen inches of the bore was lapped in a reverse taper to relieve bullet friction.

This is the first I've heard of such a practice! While I don't question your account, I seriously question the logic of the armorers who would deliberately reduce the
velocity and energy of a round, and produce both reduced accuracy and barrel life. It seems that the most minimal testing of the concept would have weighed heavily and prohibitivly against it.

You aren't the only one to think this a remarkably ill advised practice, and it didn't take long for it to be revealed as very counter productive.
British military thinking of the day put far too much emphasis on massed volley fire at extreme ranges, to the detrement of precision closer range individual marksmanship.
Remaining shootable examples of the SMLE MkI are rare, and many were rebarreled after 1917 so not many still have the reverse taper bore. One thing to look for if you ever run across one is that in extreme examples the bore can measure closer to 8mm, and sometimes these rifles were condemned as worn out because they couldn't pass the later standard .303 muzzle erosion plug gauge test even when in unfired condition.

I notice that your examples often feature historical British military rounds, and in detail that would be beyond the experience of most shooters. By any chance are you in the British Military in some capacity that woule make you privy to such detailed histories?

Most all the sources I cite can be downloaded free from the net. I've long had an interest in late 19th century fire arms designs, the Lee Enfields are just one of many, and much more detailed information can be found on their development than can be found on most any military rifle in their class.
Since the .303 cartridge was one of the first smaller bore high velocity rounds and began as a black powder load using compressed cylinders of powder, its development is especially instructive.

>The effects of erosion increase dramitically with increases in pressure and volume of gases.
>The .276 British for which the P-13 rifle was originally designed was found to burn out its bore in a fraction of the number of rounds fired compared to the .303 when both cartridges used Cordite propellant. A cartridge loaded to a lower pressure range and lower charge weight will not erode a bore nearly as fast as the same cartridge loaded to a maximum pressure range with a heavier charge of the same or similar propellant.

No arguement here! I am of course aware that typical cast bullet loads exhibit lower pressures than factory rounds, and thus have much less propensity to cause throat erosion. But the consistent gas blowby that my recovered bullets exhibited from all but the lightest loads caused me to be alert for any problems. Evidence of gas blowby that I observed began as tiny spots of erosion or etching on the base of the bullet, just in front of the gas check, and located exactly at the land engraving on the gas check. I have never understood this, as it would seem that the engraving should produce the tightest fit, and certainly far tighter than the land engraving areas. Be that as it may, the etching grew progressively more extensive until the base of the bullet was encircled, and the land engraving began to enlarge along the sides of the bullet. With so much gas blowby evident in heavy loads, it seemed prudent to be alert for evidence of bore erosion, but I never found the slightest trace.

You might try a slightly softer bullet or an over the charge card wad if you intend to use such light loads exclusively.
If your bullets are too hard stepping up the powder charge may not be enough to bump up the bullets enough to form a gas tight seal.

>Also the effects of thermal erosion are often not easily detected by the naked eye.
>Theres nothing at all unusual about a fairly low intensity cast bullet load not eroding a bore to any noticable extent, thats one of the major reasons for using cast boolit loads to begin with.

Granted, it may have been possible that erosion was present but invisible to my old eyes.

Usually early erosion is very uniform, and more often than not will erode the bottom of the grooves faster than the top of the lands, giving the appearance of a bore with little wear.
Mechanical abrasion wears away the top of the land faster than the bottom of the grooves.

>Bullet lubes are there to reduce friction which would other wise lead to leading and or mechanical erosion by means of abrasion.

I have to disagree with you there too. As a youngster, I was fed all sorts of explanations for leading. The lead was abraded off of the bullet by bore irregularities, and was soldered to the surface by the propellent gases. Or it was removed by friction, or because the lube wasn't good enough, or (ad infinitum). I reasoned that these explanations, though superficially reasonable, could not possibly all be correct. I sat out to find out exactly what mechanisms produced leading. I compressed lead against clean steel in hydraulic presses. I checked for abrasive loss by pressing bullets through barrels to check for weight loss. I simulated the passage of the bullet against the bore by chucking bullets in high speed drills. I tested with and without lubes of various types, and at low and at high temperatures. And no matter what I did, I was unable to obtain the slightest adhesion of lead to steel unless the process was sufficiently intense to produce some melting of the lead bullet. And I compared my results with that of air rifles, where lead pellets can be shot for thousands of rounds at velocities over 1000 FPS without the slightest trace of leading.

MOLTEN LEAD IS AN ABSOLUTE REQUIREMENT OF LEADING. So I turned to considering sources of heat in the rifle, which reduced to propellent gas or friction. If friction were the culpret, it should be most evident toward the muzzle, where velocity is highest. Instead, leading is generally most severe at the beginning of the bore, where propellent gas is the only significant source of heat. I started using fillers beneath the bullet to form a sort of firewall. This was successful in markedly reducing the etching and leading, though it frequently reduced accuracy. But note that these varied results were obtained with all bullets lubricated with the same type and amount of lubricant. It was a constant, and could not have been able to cause or prevent leading.

I fianlly came to the conclusion that the source of leading was the same gas erosion that produced the etching of the bullet base described above, and that the primary role of lubricants was to proovide a surface contamination of the bore that retarded adhesion of the molten microscopic droplets etched from the bullet base. I also recognize that as the temperature of the gases increase with more powerful loads, the point will be reached when the surface tension of the lead that permits soldering will be reduced enough to enable it to adhere despite any lube contamination of the surface.

Lubes do play other roles, and sometimes improtant ones: Even light loads that produce no gas etching will exhibit different accuracy potential with different lubes. I am frankly ignorant of these roles, and of how lubes perform in them.

I've cleaned a lot of lead out of old rifles, the softer the pellet the more leading, many air rifle pellets these days use very fine coatings to reduce leading, my favorite is the Beeman with antifriction coating.
The high pressure clean air or CO2 of pre charged guns blows out much fouling , but the compression generated heat of powerful spring piston guns can bake on oils to clog rifling with a laquer deposit.
In any case the bearing surface of most pellets is a tiny fraction of one percent that of even a .22 rimfire bullet.

I've fired .36 round balls without lube , when I first began BP shooting in the late sixties. When no lube was used the corners of the grooves showed streamers of lead after the first shot had burned away any preservative grease left in the bore. With even a minimum of lube over the bullets no leading occured at all.

>Other older rifles suffered microscopic pitting all over the surface of the bore due to corrosive primers. Tests run by the American Rifleman long ago indicated that bores with such surface pitting were actually more accurate when using cast bullets than a rifle of the same type with pristine bore. the microscopic pits held globules of bullet lube which under pressure acted as microscopic ball bearing greatly reducing friction and wear of the bullet surface.

This sounds reasonable, but I have seen SO many 'reasonable' explanations turn out to be worthless that I have grown quite cynical in my old age. Are you aware of any effort to verify this? I question the logic of a soft bullet being prevented from being pressed into a microscopic pit filled with lube as being superior to a hard jacketed bullet that will not be pressed into the pit in any case.

Not just reasonable, its been proven by exhaustive scientific testing. I once had a reprint of Bosworth on the Rifle which goes into great detail in testing of each of his claims, Bosworth was a noted Marine Engineer and avid shooter, and one of if not the first to mount a telescopic sight on a fire arm, though only as a test rig to prove the potential accuracy of rifled short pistol barrels. He used a surveyors transit on a removalable mounting for these tests. His investigations into metalurgy of the day are especially note worthy.

The testing recounted in the American Rifleman involved careful measurements of velocity as well as accuracy with barrels at various stages of "seasoning".

I've also noted that old military rifles who's bores show the grayish texture of age are less prone to copper fouling than a highly polished bore.
Makers of modern target rifle barrels have begun to use a similar surface texturing in their barrels to reduce jacket fouling.

If the pitting s even a tiny bit larger than the near microscopic size then the situation is reversed, with metal fouling increasing greatly.
A seasoned bore may only show a slightly graying of the metal, like an old pocket knife blade. Thats about the optimum for this effect. Any darker and the effect is reversed.

You can asked traditional Muzzle Loader shooters, they have begun to rediscover the benefits of a properly seasoned bore over a new polished bore.

[Molly]

Hi StarMetal

>I'm aware of the new age modern air rifles, but I'm talking about propelling say 180 grain cast 30 caliber bullet from a rifle barrel of about 24 inches to the velocity of say around 2600 fps or more unlubed. I'd like to see the bore after say 200 rounds.

As I said, this is quite doable with granulated cereal fillers. The fillers compact behind the bullet and positively prevent passage of propellent gas which would otherwise etch the bullet and lead the barrel. No etching means no leading, and you can run as many hundreds of bullets through it as you want, but you'll still have a bright clean unleaded bore.

Out of curiosity, why do you seem to consider the air rifle example invalid when considering leading? They can develop velocities WELL over 1000 fps, which should be more than adequate to settle the leading question. Compare their velocities with the leading one can generate from a pistol at LESS than 1000 fps: If leading can occur at low velocity, it should occur from higher velocity if all the pertinent factors are present. The fact that air rifles do not generate leading seems ample evidence that they do not encompass the critical factor. Considering the many tests that indicate that leading adhesion occurs only when the alloy has been melted, attributing leading to gas etching seems a given.

>I believe the surface tension of metals are in their liquid state. That wouldn't apply to what we are discussing. Maybe your were thinking of coefficient of friction such as in static and sliding.

No, I didn't mis-speak. All physical materials (inclucing gases) have a surface tension value, although the surface tension of liquids is admittedly the most frequently studied and used. Lead or copper alloys are no exceptions, whether they are solid or molten. The surface tension shifts with temperature, and you can actually observe this by laying a metal panel with a speck of lube on a hotplate and turing the heat on. The solid lube will be seen to have little tendency to wet the panel and spread out into a thin film at first. But as the system heats, it will melt (lowering its surface tension) and spread.

One can also easily see differences in surface tension of solid materials. Simply place several different materials (wood, copper, steel, linotype, etc) together, and have a sample of a liquid such as olive oil handy. Gently place a droplet of oil on each and observe the differences. The oil will spread rapidly on some surfaces, and slowly on others. You are probably already familiar with this in the form of a teflon frying pan: The reason nothing sticks to it is because the surface tension is so low that nothing can wet it out. You may put a droplet of oil on it, but it will just form a bead, and won't spread out at all.

In a more pertinent example, tin is used in lead alloys because it has a very low surface tension. A little bit will lower the surface tension of the alloy and allow it to flow and make good castings. However, too much tin will lower the surface tension so much that you will have solder, and lots of trouble from leading.

[Multigunner]

Gas blowby can greatly increase leading, but its not the only source of heat in the passage of a bullet up the bore.

Gas thermal transfer to the surface of the bore heats only the surface, while friction from bullet passage applies heat in a manner that can heat the entire bulk of the barrel metal at a much lower intensity.
This is most easily observed in fully automatic weapons, with propellant heat transfer heating the first few inches from breech forwards and friction of beullet passage heating the barrel closer to the muzzle.

When high temperature double base propellants were used they often heated the breech enough to cook off chambered cartridges. As nitroglycerin contents were reduced, from the high of 58% to the present 7-8% or less the heating of the breech was reduced till automatic weapons firing from a closed breech no longer poses a cook off problem, but barrel overheating remains a factor due to heating by friction of bullet passage.

Studies on heating by bullet friction were done long ago, using hydraulic rams to force bullets through rifled barrels without any heat from propellant gases.
I may have results of these tests saved to documents, but finding them will be a chore I don't wish to get into just now.

Bore heating of spring piston air rifles due to heat generated by sudden compression is a known factor, pre charged pnuematics and CO2 powered rifles on the other hand act to cool the barrel yet these can still sometimes show significant heating of the barrel due to friction if the pellet or bullet has much if any bearing surface to speak of. Waisted air gun pellets are designed to present minimal bore contact precisely because the least friction can greatly reduce velocities.
If you've noticed most air gun pellets do have a thin smear of light oil and you can feel it on your fingers after handling them. Some pellets use a dry lube, sometime impregnated into the surface. Beeman Wadcutters use a dark teflonlike coating, these are my personal favorites.

I've cleaned my opld .22 S&W 78g and was amazed at the amount of lead it had accumulated. I recently obtained a .177 cleaning rod with bronze brush for removing lead from my 177 air rifles. Removing this sort of leading greatly improves accuracy and velocity.
Special felt wads impregnated with cleansing solutions are available for regular cleaning, you fire these like a pellet and they carry away loose fouling, but a bristle brush is necessary to remove more stubborn leading.

[Molly]

Hi Multigunner,
>The Mobillube fiasco that later damaged Springfields involved a very different class of grease with very different properties.

Oh, by all means! But similar physical properties should typically generate similar mechanical effects. Not to beat a dead horse, but the tests you reported interested me.

>Because that shortened barrel allowed enough muzzle blast to mushroom the base of the fired bullets.
>His conclusion on the upsetting in the throat was based on both extrapolation of the effect of pressures at various points in bullet travel and the concave appearance of the bullet bases of those fired from a barrel of normal length.
>The experiment with shortened barrel proved sufficient pressure and acceleration forces remained to continue the upsetting action for a good way up the bore, which is why such continued acceleration can force a bullet to conform to bulged or eroded portions of the bore in the first few inches of travel, but that force drops off as the bullet reached its limit of velocity as it neared the muzzle of a full length barrel. Some pressure remained but not enough to give a sufficient G force of acceleration.

Oh, I have no quarrel with the notion that there is sufficient pressure to produce base upset in the throat with quite a few bullet types and alloys. My concern is whether this actually occurs in reality. As I've said, (and I think you did as well) no bullet can upset beyond the walls of the barrel / bore without blowing the barrel up. Modern cast bullet technology recommends sizing bullets to the greatest diameter that the throat will accomodate. Consequently, one might expect a clearance of perhaps 1/2 mil between most bullets and the throat of the bore, irrespective of absolute diameters. Upset in the bore seems highly unlikely to exceed this value, which would be most difficult to detect after the bullet has impacted a target and been recovered.

It is considerably more likely that any upset that may occur will take place within the case neck. Clearances are notably larger, though not easily quantifiable because of manufacturing tolerances, etc. However, any upset that occurs should result in a foreshortening of the base of the bullet, followed by an immediate resizing as the bullet enters the throat and bore. This resizing should produce a number of observable changes to the bullet. The gas check shank should be at least partially obliterated, much as the heel of a .22 is obliterated by base upset. It will not be protected by the belt of lube around the gas check shank because the lube will be wiped off as the bullet is resized to bore dimensions. Similarly, grease grooves should be expanded and shortened.

I see no such effects from loads with hard alloys, even with loads too powerful for even moderate accuracy.

>If the bullet base is deformed by muzzle blast inaccuracy is the result, just as it would be if the bullet base were deformed by any other means before loading.
Gas checks reduce such damage and allow stronger charges. Card over charge wads also acted to reduce damage to bullet bases and reduce blowby.

I haven't been able to figure out a method of determining exactly what happens at the muzzle with powerful loads. Speculation might include the bullet being literally bent, except that even with wild shooting, I seldom see keyholes. Another mechanism might be base upset as shown in Mann's photos, but my recovered bullets do not show any measureable expansion of the base. I don't know what happens at the muzzle, but I know something bad happens there with sufficiently powerful loads.

>From what you've said you use very light loads and your group sizes indicate that you might get better accuracy with either a slight increase in the load or a slightly softer bullet.

Not so! My initial interest in cast bullets was for big game hunting, and almost all my work was with pretty powerful loads. Accuracy was sometimes horrible before I began to learn how to make good loads, but 100 yard groups eventually settled down at about 1.5 MOA as a typical value for a five shot group. This won't win any bench matches, but is considerably better than necessary for Eastern deer hunting.

>BP target rifles in a similar velocity class printed far tighter groups than you find acceptable. One holer ten shot groups at 200 yards were not uncommon for the .32-40 target rifles of Harry Pope for one example and this without a gas check and only a thin over charge card wad. Those rifles generally used a false muzzle and a sealed blank charge rather than loading as a normal breech loader of course.

Oh, that's not quite true. BP targets from LIGHT loads could indeed exhibit remarkable accuracy, but hunting loads seldom equaled this accuracy. The only light loads I played with were worked up to entertain squirrels. For this, hitting a golf ball at 30 yards was quite sufficient. My guns have been ordinary commercial sporters, not custom built match rifles.

>Sounds like you had a very oversized throat or undersized bullet to begin with to allow that much blowby, a too hard alloy would contribute.

Not that I know of. I invariably sized bullet to the greatest diameter that would enter the throat. In 30 caliber, this was usually 0.312 inches, though it could vary somewhat between rifles. So irregardless of absolute diiameters, throat fit was pretty much a constant.

>Your instance of blowby damage confirms my previous examples of blowby damage when bullets do not bump up to seal properly. Without a proper bullet to bore seal things begin to go wrong quickly.

Perhaps I failed to mention that the blowby damage I reported occurred only with heaver loads, starting at perhaps 30-40 Krag velocities from a 30-06. However, the blowby damage did not reduce with more powerful loads, as should occur if the bullet upset. Instead, blowby progressively increased with the powder weight. These more powerful loads should have been better able to provide whatever upset might have been possible, and produced less blowby. This did not happen. Blowby and damage increased as the load increased.

>You might try a slightly softer bullet or an over the charge card wad if you intend to use such light loads exclusively.

Again, you have apparently misunderstood my goals.

>If your bullets are too hard stepping up the powder charge may not be enough to bump up the bullets enough to form a gas tight seal.

IE, hard cast bullets do not upset in the throat. That's what I've been saying.

>I've fired .36 round balls without lube , when I first began BP shooting in the late sixties. When no lube was used the corners of the grooves showed streamers of lead after the first shot had burned away any preservative grease left in the bore. With even a minimum of lube over the bullets no leading occured at all.

Quite believable! I believe that one of the mechanisms of bullet lubes is to 'contaminate' the surface of the bore and prevent adhesion, just as dirty metal is difficult to solder.

>I've also noted that old military rifles who's bores show the grayish texture of age are less prone to copper fouling than a highly polished bore.
>Makers of modern target rifle barrels have begun to use a similar surface texturing in their barrels to reduce jacket fouling.
>If the pitting s even a tiny bit larger than the near microscopic size then the situation is reversed, with metal fouling increasing greatly.
A seasoned bore may only show a slightly graying of the metal, like an old pocket knife blade. Thats about the optimum for this effect. Any darker and the effect is reversed.

Now THAT's fascinating! I hadn't heard of this at all. What processes are used to provide the surface texturing?

[303Guy]

>I've also noted that old military rifles who's bores show the grayish texture of age are less prone to copper fouling than a highly polished bore.
>Makers of modern target rifle barrels have begun to use a similar surface texturing in their barrels to reduce jacket fouling.
>If the pitting s even a tiny bit larger than the near microscopic size then the situation is reversed, with metal fouling increasing greatly.

I've missed a bit but this last comment requires a response. I have a rust pitted, two-groove Lee Enfield that shoots with amazing accuracy and zero copper fouling. I do, however lube the bullet bases (chamfered) with 'waxy-lube' prior to seating. I suspect that small amounts of lube are trapped in the pits and this lubes the next round. Or maybe the pits trap powder soot which does the same thing. But this bore is a little more than 'textured'. It did require fire-lapping though. I also chopped off the last inch or so of barrel and re-crowned it.

These more powerful loads should have been better able to provide whatever upset might have been possible, and produced less blowby.

Just a thought on this one .... higher pressure would increase the pressure of the obturating boolit against the bore thus increasing leading damage and possibly creating gas blow-by passages. Just a thought.

I do know that if my paper patch loads in my rust damaged bore Pig Gun are too powerfull the patch pails and leading occurs. Not the streaking type leading one often see's but an even grey deposit of lead throughout the bore and even a star shaped pattern on the muzzle. This with fast powder in a short barrel.

[AriM]

Wouldn't it be prudent to say that obturation being the cause or not, boolits take on the shape of the bore? I think that is proof enough. Maybe I am thinking too simple. I am nowhere near as experienced as the debaters, but plain logic is plain logic. Flow mechanics have not magically changed, have they?

It's amazing how Newton predicted all of these laws and relationships, far before any qualified test equipment was available. They continue to prove out on a daily basis. His observations and generalizations fascinate me.

By these tokens, wouldn't it be safe to assume that some form of obturation is happening. If it's due to powder charge or unequal pressure, does not seem to be important. The bottom line is that the lead deforms during it's travel.

Now isn't it also safe to say, that many tests have proven that something as simple as a crimp die can "obturate" a projectile, before it's even fired?

It would seem to me, that the reason for lead as a primary projectile substance, is due to it's physical property to

1. easily deform
2. retain weight
3. rapidly expand/contract and radiate heat

I am not sure how obturation can even be a debate. The fact that we cast boolits is simple proof. The fact that we swage boolits in sizing dies, is simple proof. The fact that we match alloy to pressure is simple proof. The fact that we can recover the projectiles and see etched rifling is simple proof.

Am I missing something that transcends simple logic here????

I think Newton is rolling in his grave.....could some possibly add that as a poll choice?

Sorry for being snarky, just trying to understand.

[303Guy]

Studies on heating by bullet friction were done long ago, ...

I have a rust damaged bore 22 hornet with a .223 bore through which I shoot .224 bullets. One day I decided to develope a subsonic load. Well, sometimes the bullet would stop in the bore. These would come out easily. Others made it through and one example came to rest in a non-cotton fabric where it melted itself fast. These bullets also showed heat staining on the copper jacket. I'm not so sure about bullet friction heating the barrel deeper than any other source of heat. I have another story about the hornet - my load used to heat the barrel faster than a high power rifle. Then one day, I increased the powder charge a little and the barrel stayed cool! Go figure.

[Multigunner]

Quite believable! I believe that one of the mechanisms of bullet lubes is to 'contaminate' the surface of the bore and prevent adhesion, just as dirty metal is difficult to solder.

When Cordite was first invented it was found to generate enough heat both by the heat of the gas and friction of increased velocity that copper or cupro-nickel jacket material would fuse directly to the bore steel making it almost impossible to remove. When they were testing another propellant which left more fouling they found that when a cordite propelled round was fired alternately along with the other rounds little or no metal fouling resulted. They found this to be due to carbon fouling insulating the bore steel from direct metal to metal contact.
Afterwards they added a 5% mineral jelly content to the basic Nitroglycerin/Nitrocellulose formula, the mineral jelly producing a thin skin of carbon fouling to reduce metal fouling.
Flake cordite used in pistol cartridges and blank cartridges does not contain mineral jelly.

It is considerably more likely that any upset that may occur will take place within the case neck. Clearances are notably larger

There is some upset while the bullet is still in the case neck, some cartridge/bullet combinations more or less than others. On other threads I've cautioned owners of older military rifles to throughly clean chamber necks of built up carbon and lead that can choke the case neck causing increased pressures.

When the Boers received a shipment of 7mm ammunition loaded in non standard 53mm length cases they had a rash of blown up mausers.
The bullets were upsetting in the unsupported 4mm gap ahead of the throat, with a ring of jacket material being stripped off to telescop over the next bullet fired, greatly increasing pressures.
A stop gap fix was to use a thick grease on the bullets to fill the gap long enough for the bullet to clear it. The incompressible grease acting to slow the expansion of the bullet til clear of the gap.

[303Guy]

When the Boers received a shipment of 7mm ammunition loaded in non standard 53mm length cases they had a rash of blown up mausers.
The bullets were upsetting in the unsupported 4mm gap ahead of the throat, with a ring of jacket material being stripped off to telescop over the next bullet fired, greatly increasing pressures.

So, that's what caused those "Kort Nek" blow-ups!

Flow mechanics have not magically changed, have they?

No, but we might only be beginning to understand it.

Now isn't it also safe to say, that many tests have proven that something as simple as a crimp die can "obturate" a projectile, before it's even fired?

No. Obturate means to seal or block, i.e, obstruct. It does not mean the boolit or bullet deforms, just that it expands enough to seal the bore. Boolit upset means the boolit has actually deformed due to plastic flow. What's wrong with out understanding of Neutonian physics is time. It takes time for metals to undergo plastic deformation. Elastic deformation - which is reversable - can be very fast (and is not permanent).

[StarMetal]

>I haven't been able to figure out a method of determining exactly what happens at the muzzle with powerful loads. Speculation might include the bullet being literally bent, except that even with wild shooting, I seldom see keyholes. Another mechanism might be base upset as shown in Mann's photos, but my recovered bullets do not show any measureable expansion of the base. I don't know what happens at the muzzle, but I know something bad happens there with sufficiently powerful loads.

Now we're talking something that I have a fight in. Specifically shooting the 6.5 Swede at very high velocities with it's exceptionally fast twist. There was a theory here that the alloy bullets bent and flew off into wonder wonder land. One analogy that was given was to chuck a length of copper wire into a variable speed drill and first spin the drill at a low rpm. This would simulate a low velocity alloy load and the wire stays fairly straight. Then spin the wire at a high rpm which would simulate a high velocity alloy bullet and the wire then becomes more like a propeller. Three things wrong with that analogy...1. The barrel isn't holding onto the bullet, it's always moving forward..2. It simply doesn't happen that way...and 3. I proved that wrong with my high velocity accurate shooting of the 6.5 Swede (and I might add other 6.5 calibers with very fast twist) which you may have read about on this forum.

Nope on this one you have are not correct. If the alloy can survive the trip down the bore it's not going to bent at the muzzle nor in flight. It can bent went it encounters an obstacle.

I do believe you are off on pellets not leading the bores of air rifle and I believe Multigunner is in agreement with me there also.

Multigunner is, in my opinion, also correct that there is lots of friction heat created by the bullet in passage through the bore. I've also had heated debated on this in another area of why are casings from a semi auto firearm much much hotter then from manually operated ones. My reasons are because of two things...1. one heat from the powder combustion..and 2. heat from friction of being extracted violently from the chamber. It is No 2 that I say causes the most heat.

[Molly]

Hi AriM,

>By these tokens, wouldn't it be safe to assume that some form of obturation is happening. If it's due to powder charge or unequal pressure, does not seem to be important. The bottom line is that the lead deforms during it's travel.

You may be failing to distinguish between deformation and obturation. Obturation is a special case of deformation, wherein the base of the bullet is expanded by the pressure of the round, to the limits of the chamber and bore. Deformation is ANY change in shape of the bullet.

>It would seem to me, that the reason for lead as a primary projectile substance, is due to it's physical property to
>1. easily deform
>2. retain weight
>3. rapidly expand/contract and radiate heat

Actually, none of these properties are as important to a bullet's performance as its density. The high density of lead enables it to maintain velocity and flatten trajectory better than most other metals, all else being equal. There are better metals from a performance perspective though: Gold is more dense, and some aristocrats actually had gold bullets for their muzzle loading arms. However, gold is not an optimal choice from other perspectives. (VBG)

>I am not sure how obturation can even be a debate. The fact that we cast boolits is simple proof.

Of what? That lead will melt and pour? That's not in question.

>The fact that we swage boolits in sizing dies, is simple proof.

Of what? That lead is maleable? Again, that's not in question.

>The fact that we match alloy to pressure is simple proof.

Again, of what? That if we soften an alloy enough, it can be made to obturate? Still not in question.

>The fact that we can recover the projectiles and see etched rifling is simple proof.

Seems to me that any etching remaining on a recovered bullet drive band is ample proof that obturation or expansion did NOT take place, as it would have wiped the etching away.

[felix]

"If the alloy can survive the trip down the bore it's not going to be bent at the muzzle nor in flight". Joe, that's true when the ENTIRE projectile leaves the gun instantaneously. ... felix

[StarMetal]

"If the alloy can survive the trip down the bore it's not going to be bent at the muzzle nor in flight". Joe, that's true when the ENTIRE projectile leaves the gun instantaneously. ... felix

Felix,

I'm finding that my alloy of 50/50 (air cooled I might add) can take far more abuse going down the bore of my 6.5 Swede then many of us have thought. In experimental testing of new loads I found (without dangerous pressures or blowing of primers, etc.) that I had exceeded the speed limit so to say with one load. I had that little Kurtz going over 2800 fps, not stripping in the bore, not leading the bore, and staying on the target paper, alone the whole back stop. More going on here then meets the eye.

You are correct in stating "when the whole projectile leaves the muzzle" and if you can remember the picture I posted a long time ago of a pristine retrieved bullet fired from my Steyr M95 and bullet had raised ridges (past the widest diameter of the bullet) near the pressure or force side of the lands. One would thing "How could that be when it's contained in the bore". Well my answer is we know the bullet is spinning, even when it has entirely left the muzzle, and thus the edge or mouth of the muzzle raised that ridge until it let go of the bullet.

[Molly]

Hi StarMetal

>>I don't know what happens at the muzzle, but I know something bad happens there with sufficiently powerful loads.

>Now we're talking something that I have a fight in. Specifically shooting the 6.5 Swede at very high velocities with it's exceptionally fast twist. There was a theory here that the alloy bullets bent and flew off into wonder wonder land. ... Three things wrong with that analogy...and 3. I proved that wrong with my high velocity accurate shooting of the 6.5 Swede ... which you may have read about on this forum.

No, but I don't doubt you for a moment. In fact, I found the 6.5 Swede to work quite well with high velocity hard cast bullets over a pinch of CoW, despite lacking lube, sizing or gas check.

>Nope on this one you are not correct. If the alloy can survive the trip down the bore it's not going to bent at the muzzle nor in flight. It can bent went it encounters an obstacle.

Nor did I say it did. It was just one speculation among others, presented as something to consider, not as a definitive answer to the problem of what muzzle blast does. I explicitly noted that I had not been able to come up with any tests that would tell me what happens at the muzzle.

>I do believe you are off on pellets not leading the bores of air rifle and I believe Multigunner is in agreement with me there also.

This could be just a semantic quibble. I know that felt wads are used in air rifles, purportedly to remove leading. I think that's delusional. No leading I ever dealt with would be removed by a felt wad, particularly in a single pass. Indeed, some of it could hardly be removed by steel wool, applied vigorously over a long period of time. Now if you want to consider traces of loose lead dust as leading, I can go along with you. But not if you are referring to adherent leading.

>Multigunner is, in my opinion, also correct that there is lots of friction heat created by the bullet in passage through the bore.

Possibly so, but is the heat generated anywhere near the order of magnitude of the heat imparted by the propellent? I'd be surprised! The total heat imparted is less than about 500 or 600 degrees F. If it were more, the bullet would melt in the bore.

>I've also had heated debated on this in another area of why are casings from a semi auto firearm much much hotter then from manually operated ones. My reasons are because of two things...1. one heat from the powder combustion..and 2. heat from friction of being extracted violently from the chamber. It is No 2 that I say causes the most heat.

May I suggest another thought? The autoloading feature will eject the freshly heated case before it has a chance to bleed much heat to the barrel. A manually operated action will not eject the case until it has had at least a few seconds to dump its heat. As a result, the auto-ejected case still has most of its heat, and is hotter. The manually ejected case has lost a significant portion of its heat, and is cooler.

I've done some actual testing along this line. You can buy thin, wax impregnated paper strips that are calibrated by the melting point of the wax. These strips will fit between a case and the chamber walls. On firing, you can determine whether or not the case reached the temperature of the wax in the strip you tested. If so, use a higher temperature strip next time. If not, use a lower melting strip. I got into this because wax will flow from prressure as well as temperature, and I was trying to develop a pressure measurement system. I got good reproducability, and it was little trouble to duplicate the readings obtained with factory ammo. But there were always questions about the thickness and hardness of the case that cast doubt on the validity of the results. In the end, I gave it up, but it was a lot of fun while it lasted.

[Multigunner]

So, that's what caused those "Kort Nek" blow-ups!

I've seen alternate theories presented, more like hypothesis really since the alternates have no access to the rifles or ammo while the Boers did.

I can only go by the written descriptions, but here is how I see it happening.

When the bullet bumped up on the way out of the case neck the unsupported portion of the jacket swelled into a ring ahead of the case mouth, separating from the core at that point and over stressing the jacket which was likely work hardened from crimping pressures. Breakage of bullet jackets at crimping grooves was a not uncommon problem.
The rear portion of the jacket having broken free with its expanded front edge catching the end of the chamber mouth would strip away from the core, the bullet with blown through section of core then departs, with little chance of hitting anything.
The operator cycles the bolt extracting the empty case but leaving a short section of tube stuck in the chamber neck.
When the next round enters the chamber the bullet telescopes into the tube and wedges firmly, the bullet is pushed back into the case compressing the powder charge.
When we shoot for recreation, if we have difficulty chambering a round we back off and check the chamber, in the heat of battle the shooter would use any means necessary to jam that danged cartridge home.
Since previous military fire arms in use in Africa were often plagued by bent coiled brass cases, verdgris, swollen shotshells, etc, recalricant cartridges were a simple fact of life, and raised no red flag.

When our intrepid warrior finally got that blasted bolt closed and turned home, he now had a oversized projectile jammed deeply into the case, with a tightly compressed charge of an already very powerful cartridge.

I've never seen a good explanation of just how those kort nek 7X53 cartridges ended up in Africa, nor any rifle chambered for such a cartridge.
Theres speculation that the 7mm had originally been intended to use the 53mm case length and these cases had been rushed into production before the specs were finalized, then left in storage till some means of using them came along. If not for the Boers buying up anything that would shoot those short cases would probably have been scrap metal.
The cases may also have been formed from drawn blanks intended for the 7.65X53, with the manufacturer not taking the possible dangers into account.

For whatever reason this incident would indicate that its not wise to use a case thats too short.

I remember that a similar problem has been reported when .38 Super Auto cartridges were fired in a .38 Special or .357 magnum Chamber.
Firing .32 ACP in a .32 S&W long might cause the a pressure rise as well, but not to the same extent since the .32 ACP is such a low pressure cartridge with a stout jacketed bullet.

There are revolvers with chambers reamed in a gentle taper, which allow cartridges of the same general .357/9mm bullet size but cases of varying lengths to be fired safely.

[StarMetal]

Hi StarMetal

>>I don't know what happens at the muzzle, but I know something bad happens there with sufficiently powerful loads.

>Now we're talking something that I have a fight in. Specifically shooting the 6.5 Swede at very high velocities with it's exceptionally fast twist. There was a theory here that the alloy bullets bent and flew off into wonder wonder land. ... Three things wrong with that analogy...and 3. I proved that wrong with my high velocity accurate shooting of the 6.5 Swede ... which you may have read about on this forum.

No, but I don't doubt you for a moment. In fact, I found the 6.5 Swede to work quite well with high velocity hard cast bullets over a pinch of CoW, despite lacking lube, sizing or gas check.

>Nope on this one you are not correct. If the alloy can survive the trip down the bore it's not going to bent at the muzzle nor in flight. It can bent went it encounters an obstacle.

Nor did I say it did. It was just one speculation among others, presented as something to consider, not as a definitive answer to the problem of what muzzle blast does. I explicitly noted that I had not been able to come up with any tests that would tell me what happens at the muzzle.

>I do believe you are off on pellets not leading the bores of air rifle and I believe Multigunner is in agreement with me there also.

This could be just a semantic quibble. I know that felt wads are used in air rifles, purportedly to remove leading. I think that's delusional. No leading I ever dealt with would be removed by a felt wad, particularly in a single pass. Indeed, some of it could hardly be removed by steel wool, applied vigorously over a long period of time. Now if you want to consider traces of loose lead dust as leading, I can go along with you. But not if you are referring to adherent leading.

>Multigunner is, in my opinion, also correct that there is lots of friction heat created by the bullet in passage through the bore.

Possibly so, but is the heat generated anywhere near the order of magnitude of the heat imparted by the propellent? I'd be surprised! The total heat imparted is less than about 500 or 600 degrees F. If it were more, the bullet would melt in the bore.

>I've also had heated debated on this in another area of why are casings from a semi auto firearm much much hotter then from manually operated ones. My reasons are because of two things...1. one heat from the powder combustion..and 2. heat from friction of being extracted violently from the chamber. It is No 2 that I say causes the most heat.

May I suggest another thought? The autoloading feature will eject the freshly heated case before it has a chance to bleed much heat to the barrel. A manually operated action will not eject the case until it has had at least a few seconds to dump its heat. As a result, the auto-ejected case still has most of its heat, and is hotter. The manually ejected case has lost a significant portion of its heat, and is cooler.

I've done some actual testing along this line. You can buy thin, wax impregnated paper strips that are calibrated by the melting point of the wax. These strips will fit between a case and the chamber walls. On firing, you can determine whether or not the case reached the temperature of the wax in the strip you tested. If so, use a higher temperature strip next time. If not, use a lower melting strip. I got into this because wax will flow from prressure as well as temperature, and I was trying to develop a pressure measurement system. I got good reproducability, and it was little trouble to duplicate the readings obtained with factory ammo. But there were always questions about the thickness and hardness of the case that cast doubt on the validity of the results. In the end, I gave it up, but it was a lot of fun while it lasted.

Molly

Afraid I can't be aboard on the semi auto cases are hotter because they are ejected from the chamber so fast they are still hot. One can shuck a case from the chamber with a bolt gun pretty fast and the case is no ways near as hot at the semi auto. You mean to tell me that the time it takes to bolt a rifle that the heat from the case has dissipated to the rifle? I doubt that much. Look how long semi auto casings stay very hot on the ground. The cooling of the case to air is pretty good being it's exposed to the cooling air both internally and externally.

If you doubt friction can cause that much heat are you aware of welding metal by friction? Also do you have a clue how how the brakes get on an airliner? In the case of the airliner we're talking about thousands of degree....almost instantly.

Nope, you're off on that one. By the way I'd love to see you shoot a Swede at high velocity with some degree of accuracy with a normal alloy without lube or gas checks. That's not crowing on my part, I just find it hard to believe. I know there are some that can shoot bare alloy bullets with success.

[AriM]

Hi Molly,


>You may be failing to distinguish between deformation and obturation. Obturation is a special case of deformation, wherein the base of the bullet is expanded by the pressure of the round, to the limits of the chamber and bore. Deformation is ANY change in shape of the bullet.


this is the basis of my point. i understand the defined differences between "obturation" and deformation. however, I am trying to say that, for whatever reason lead deforms when pushed through the barrel. it seems to me, that this being due to obturation or other "unknows" is moot. why would it make a dramatic difference? again I am oversimplifying and don't want to lead you to believe I don't understand the differences. none the less, the boolit deforms to fit the bore.

>Actually, none of these properties are as important to a bullet's performance as its density. The high density of lead enables it to maintain velocity and flatten trajectory better than most other metals, all else being equal. There are better metals from a performance perspective though: Gold is more dense, and some aristocrats actually had gold bullets for their muzzle loading arms. However, gold is not an optimal choice from other perspectives. (VBG)

well I had hoped that my key point of "ability to retain weight" would follow suit with what you are saying. I do understand that density (hence weight in an appropriate size) is a primary asset of Pb.

>I am not sure how obturation can even be a debate. The fact that we cast boolits is simple proof.

Of what? That lead will melt and pour? That's not in question.

>The fact that we swage boolits in sizing dies, is simple proof.

Of what? That lead is maleable? Again, that's not in question.

>The fact that we match alloy to pressure is simple proof.

Again, of what? That if we soften an alloy enough, it can be made to obturate? Still not in question.

>The fact that we can recover the projectiles and see etched rifling is simple proof.

>Seems to me that any etching remaining on a recovered bullet drive band is ample proof that obturation or expansion did NOT take place, as it would have wiped the etching away.



your above assumptions, about my statements (hate to be rude, but you did say something about assumptions earlier in this thread) are partially correct. except for the last one.

if obturation occurs then the projectile would take the shape of the bore. lands and grooves. it would be my inclination to believe, that obturation continues to happen even after the boolit leaves the muzzle. that being my theory/analysis the boolit would be etched with the rifling pattern at the very end of the barrel (muzzle). this recovered boolit would show these signs. UNLESS, gas blow-by / flame cutting stripped them off. does this sound logical. i am not trying to post a rebuttal or argument, simply trying to give you an idea of where I am coming from....and hopefully, understand where you are coming from.

Richard Lee wrote (modern reloading 2) that he witnessed lead streaking from a boolit, that was inappropriate for the pressure curve encountered. he goes on to say that he further tested this by charging even higher. the boolit exploded in flight and "broke the windshield of his new barracuda". I think this kind of proves that obturation and deformation continue to occur during the boolits entire travel. my only guess would be that this is due to a jet of hot gasses that follow the boolit, or are generated by a high/low pressure zone in front of and behind the boolit. it all seems to be much more complex than we are all making it out to be.

I personally believe that obturation and deformation are due to specific pressure curve effects on specific alloys. i.e. too little pressure for the boolits hardness, and the boolit will not bump up and seal the bore and will fail in the barrel (at some point). too much pressure and the boolit with bump up, but be followed by a trail of gasses. when the boolit no longer has a surface (harder than it) to expand against (leaves the muzzle) it will also fail (due to gasses).


it is my opinion, based on testing and limited experience, that the alloy MUST match the pressure curve of the charge and all of the associated variables (some of which are unknowns). in this scenario, the boolit bumps to seal the bore. after all we can't really cast boolits with the rifling in them already...(well Lee does make the REAL minnie ball) it's not practical, or worth the time. therefore the boolit (properly sized or not) does obturate, as does a boolit of imperfect size. in any event obturation is critical to stop failure of the projectile (in the ways I described above). I hope this is cogent....

so it seems that no one, has ever offered conclusive proof that any of these phenomenon occur. only speculation based on observation. my observations and understanding of flow dynamics and the effects of pressure on metals (family has been in metalworking for 2 generations, certainly not saying I am an expert) would lead me to believe that obturation DOES occur. that obturation is a form of deformation. it is hard for us to argue that the boolit does in fact deform. from casting, all the way to the target. with MANY points in between.

maybe we are arguing the same point, and it's an issue of terminology. I am still not quite sure what your conclusion is. you believe that obturation does not occur, yet you emphatically state that deformation occurs during the powder expansion/ignition and all along the bore, with many points to illustrate why this happens. ok, fair enough. if a smooth or rough bore cause deformation of some kind (which you agree to) and the projectiles travel to that point of the bore is under the power/pressure of a powder charge and it's associated gasses, wouldn't that be obturation??


P.S. I think that Richard Lee's chapters on this subject (modern reloading 2) are the best explanation of these phenomenon. I don't want to make assumptions, but you have read these chapters (7-10 I believe)? He breaks this down, with limited scientific analysis (i agree that it is not complete) and with countless hours and years of experience. also a lifetime of access to the industry, far beyond what any of us have. I think it's not possible to overlook his findings. He simply is more of an authority on this subject, than all of us combined (IMO). His findings have gone a long way to change some of my opinions of cast boolits and pressure curves. I hope you can offer me proof, beyond Mr. Lee's that he is incorrect. I am eager for you to change my opinions, in the same way Mr. Lee has....let's keep the dialogue going and keep it friendly. We are all on that same team

:


P.S.S. this is grossly oversimplified, but it's a definition, none the less (see below)
http://en.wikipedia.org/wiki/Obturate


P.S.S.S (lol) this is your own statement, in rebuttal to mine


>The fact that we match alloy to pressure is simple proof. (Ari)

Again, of what? That if we soften an alloy enough, it can be made to obturate? Still not in question.
(Molly)

you say that obturation is possible, probable and DOES happen in your answer....but then later on you say obturation doesn't happen....which one is it?

[StarMetal]

Hi Molly,


>You may be failing to distinguish between deformation and obturation. Obturation is a special case of deformation, wherein the base of the bullet is expanded by the pressure of the round, to the limits of the chamber and bore. Deformation is ANY change in shape of the bullet.


this is the basis of my point. i understand the defined differences between "obturation" and deformation. however, I am trying to say that, for whatever reason lead deforms when pushed through the barrel. it seems to me, that this being due to obturation or other "unknows" is moot. why would it make a dramatic difference? again I am oversimplifying and don't want to lead you to believe I don't understand the differences. none the less, the boolit deforms to fit the bore.

>Actually, none of these properties are as important to a bullet's performance as its density. The high density of lead enables it to maintain velocity and flatten trajectory better than most other metals, all else being equal. There are better metals from a performance perspective though: Gold is more dense, and some aristocrats actually had gold bullets for their muzzle loading arms. However, gold is not an optimal choice from other perspectives. (VBG)

well I had hoped that my key point of "ability to retain weight" would follow suit with what you are saying. I do understand that density (hence weight in an appropriate size) is a primary asset of Pb.

>I am not sure how obturation can even be a debate. The fact that we cast boolits is simple proof.

Of what? That lead will melt and pour? That's not in question.

>The fact that we swage boolits in sizing dies, is simple proof.

Of what? That lead is maleable? Again, that's not in question.

>The fact that we match alloy to pressure is simple proof.

Again, of what? That if we soften an alloy enough, it can be made to obturate? Still not in question.

>The fact that we can recover the projectiles and see etched rifling is simple proof.

>Seems to me that any etching remaining on a recovered bullet drive band is ample proof that obturation or expansion did NOT take place, as it would have wiped the etching away.



your above assumptions, about my statements (hate to be rude, but you did say something about assumptions earlier in this thread) are partially correct. except for the last one.

if obturation occurs then the projectile would take the shape of the bore. lands and grooves. it would be my inclination to believe, that obturation continues to happen even after the boolit leaves the muzzle. that being my theory/analysis the boolit would be etched with the rifling pattern at the very end of the barrel (muzzle). this recovered boolit would show these signs. UNLESS, gas blow-by / flame cutting stripped them off. does this sound logical. i am not trying to post a rebuttal or argument, simply trying to give you an idea of where I am coming from....and hopefully, understand where you are coming from.

Richard Lee wrote (modern reloading 2) that he witnessed lead streaking from a boolit, that was inappropriate for the pressure curve encountered. he goes on to say that he further tested this by charging even higher. the boolit exploded in flight and "broke the windshield of his new barracuda". I think this kind of proves that obturation and deformation continue to occur during the boolits entire travel. my only guess would be that this is due to a jet of hot gasses that follow the boolit, or are generated by a high/low pressure zone in front of and behind the boolit. it all seems to be much more complex than we are all making it out to be.

I personally believe that obturation and deformation are due to specific pressure curve effects on specific alloys. i.e. too little pressure for the boolits hardness, and the boolit will not bump up and seal the bore and will fail in the barrel (at some point). too much pressure and the boolit with bump up, but be followed by a trail of gasses. when the boolit no longer has a surface (harder than it) to expand against (leaves the muzzle) it will also fail (due to gasses).


it is my opinion, based on testing and limited experience, that the alloy MUST match the pressure curve of the charge and all of the associated variables (some of which are unknowns). in this scenario, the boolit bumps to seal the bore. after all we can't really cast boolits with the rifling in them already...(well Lee does make the REAL minnie ball) it's not practical, or worth the time. therefore the boolit (properly sized or not) does obturate, as does a boolit of imperfect size. in any event obturation is critical to stop failure of the projectile (in the ways I described above). I hope this is cogent....

so it seems that no one, has ever offered conclusive proof that any of these phenomenon occur. only speculation based on observation. my observations and understanding of flow dynamics and the effects of pressure on metals (family has been in metalworking for 2 generations, certainly not saying I am an expert) would lead me to believe that obturation DOES occur. that obturation is a form of deformation. it is hard for us to argue that the boolit does in fact deform. from casting, all the way to the target. with MANY points in between.

maybe we are arguing the same point, and it's an issue of terminology. I am still not quite sure what your conclusion is. you believe that obturation does not occur, yet you emphatically state that deformation occurs during the powder expansion/ignition and all along the bore, with many points to illustrate why this happens. ok, fair enough. if a smooth or rough bore cause deformation of some kind (which you agree to) and the projectiles travel to that point of the bore is under the power/pressure of a powder charge and it's associated gasses, wouldn't that be obturation??


P.S. I think that Richard Lee's chapters on this subject (modern reloading 2) are the best explanation of these phenomenon. I don't want to make assumptions, but you have read these chapters (7-10 I believe)? He breaks this down, with limited scientific analysis (i agree that it is not complete) and with countless hours and years of experience. also a lifetime of access to the industry, far beyond what any of us have. I think it's not possible to overlook his findings. He simply is more of an authority on this subject, than all of us combined (IMO). His findings have gone a long way to change some of my opinions of cast boolits and pressure curves. I hope you can offer me proof, beyond Mr. Lee's that he is incorrect. I am eager for you to change my opinions, in the same way Mr. Lee has....let's keep the dialogue going and keep it friendly. We are all on that same team

:


P.S.S. this is grossly oversimplified, but it's a definition, none the less (see below)
http://en.wikipedia.org/wiki/Obturate

I had always wondered if the TC Maxi-Ball indeed did bump up like they said. I started out on tests to find if they did. You now the majority of that bullet fits into the bore quite easily and only the front band on the nose engraves. So finally I was able to retrieve some and they did show rifling on all the bearing bands.

Shooting hollow base bullets too fast, or with too much pressure, blows the skirts off them....we know this.

One final thing we've all heard if you're gangster and you shoot someone just ruin the muzzle (or crown) of your barrel, or even saw off the end of the barrel, it you don't want to get rid of the firearm and forensics can't determine if the bullet was fired from such gun. Meaning the last marks on the bullet are from the muzzle, so even if the bore is larger there, there must be some obturation going on in the entire length of the barrel....in other words constant pressure keeping it obturated.