This article was written by the late, longtime CBA member, Ken Mollohan and was published in the July/Aug 1997, #128 issue of the Fouling Shot.
Upset in cast bullets has been around a long time. Early experimenters, using muzzle loading rifles, tried many schemes to force undersized balls to expand and take the rifling, but a Frenchman, Captain E. C. Minie had the first real success. Captain Minie employed an iron cup that was driven forward into the hollow base of a conical bullet upon ignition of the powder charge, expanding the base of the bullet to fit the bore. The Minie ball made possible the accurate rifled muskets that could reliably hit individual men hundreds of yards away. Even later, double-rest heavy bench rifles, weighing 20 to 40 pounds, worked best with two-piece swaged lead bullets with bases made of the softest lead to assure expansion. Some men could cut their initials into a 200-yard target with such outfits. That's accurate by any standard! The best rifles and marksmen we have today would be hard put to match it, but, today the expanding base is condemned as a major cause of inaccuracy!
How did expanding bases go from giving the best possible accuracy, to their current reputation for destroying accuracy? Well, to be specific, it is almost entirely the work of one man, Dr. Howard Mann. If you haven't read his book, 'The Bullet's Flight from Powder to Target, you should order a copy right now. Dr. Mann was one of the few truly scientific investigators into the factors affecting accuracy, and his book is still the best on the subject. He was the first to point out that the major cause of poor accuracy is inconsistent bullets. He also found that one of the reasons for inaccurate bullets was the way they upset in the bore. He recovered and measured fired bullets, discovering that the more the base of the bullet is out of square with the body, the further away the bullet will strike from the impact of a bullet with a perfectly square base, and he was right!
Dr. Mann also showed that flaws in the base of the bullet are far more injurious to accuracy than similar flaws in the nose of the bullet. He would drill holes in bullets to duplicate defects and by orienting these defects in the chamber, he could produce large groups like donuts, or he could shoot small groups and move the groups around on the target at will, without changing the sights in any way. Today's shooters equate large groups with damaged bases, and have locked onto the idea that for good accuracy, the base of the bullet must be perfectly formed and perfectly square to the axis of the bullet; but, that's not what Dr. Mann said. He said that the bullet had to be consistent, not perfect. His book shows many examples of fine accuracy with deliberately damaged bullets. He purposely damaged the muzzle of a rifle with a hammer and a punch to prove the point. The punch mark cut a huge groove, from nose to base, in every bullet he fired. This obviously destroyed the balance of the bullet, yet he reported that accuracy was still good; he only had to shift his sights to match a new point of impact.
Dr. Mann believed that the pressure from the burning gunpowder upset the base of the bullet in the throat of the rifle "like a hammer blow on a ball of putty." He tried to prove this by firing bullets from shortened barrels. Some of them were so short that the end of the bullet actually projected out of the muzzle before the trigger was pulled! And brother, did he get upset bases! His bullets looked like opened umbrellas! Even heavy .30 caliber jacketed military bullets were badly upset. The case seemed open and shut: If the pressure of the load is high enough to upset the base of the bullet, it will be unbalanced and inaccurate. Period!
Scuse me, Dr. Mann . . . . Those upset bullets in your photo are a lot bigger than the throat of the rifle. Looks to me like they expanded after they left the throat. Actually, it looks like they didn't expand much until after they got out of the bore altogether ... Oh, I see. It just shows that the pressure in the throat is high enough to make even a jacketed bullet expand as much as it possibly can.
Hmmm. If jacketed bullets expand with high pressures too, why do they shoot so much better than cast bullets. Oh, the softer bullet can't take the pressure as well as the tougher jacketed bullet, and naturally it deforms more and shoots worse? Hmmm. But if jacketed bullets and cast bullets both expand to fit the same throat and the same bore, aren't they deformed exactly the same, no matter what their strength? And, how come you can load a cast bullet to 40,000 psi in an Ml carbine and get good accuracy, but the same bullet isn't worth a hoot at 40,000 psi in a Ml Garand? Won't the amount of upset and accuracy loss be the same in both guns when the deforming pressure is the same? And looky hyar, Doc: Look at these .308 caliber jacketed bullets that I shot in a 7.65 Argentine Mauser. It is obvious that the bullets were rubbing on the lands, but it hardly touched the grooves. If the base upsets completely like you said, why aren't there contact marks all the way around the bullet? And how do boat-tailed bullets make it through the throat without . . . Oww! My ear! No need to be that way about it, Doc! I wuz jest asking!
Like a lot of other shooters, I've done a fair amount of bullet recovery too. I've fired into swimming pools and mountain streams, swimming down to recover the bullets. I've even shot guns completely underwater, much to the dismay of some bluegills. I've recovered bullets from dirt and deer, from wood, sand, snow, sawdust and pretty near everything in between. With low pressure loads or with soft bullets, what I found pretty much goes along with Dr. Mann's findings, even if I do have some questions about the conclusions he drew from the data. But, he dealt mostly with low pressure loads, -the .30-40 Krag was a pretty hot number in his day- and sometimes his results don't translate too well in high pressure and high velocity cast bullet loads.
Oh, Dr. Mann's tests and reports are excellent, and still completely valid; however, we have so deified him, that some people look at a loss of accuracy and jump to the conclusion that they've exceeded the strength of the bullet and are upsetting the bullet base. After all, if Dr. Mann said that is what causes inaccuracy, who are mere mortals to say otherwise?
Well, I have recently read articles by a number of competent people who feel that matching the strength of the bullet to the pressure of the load to get some upset gives them the best accuracy; and don't forget those Minie balls or black powder bench guns. A lot of things can injure accuracy besides base upset. We shouldn't be so quick to assume that poor accuracy means the base is upsetting.
I think it was Gen. Julian Hatcher who reported some tests in which he plugged the bore of a .30-06, and tried to clear it with a case that had the bullet and part of the powder charge removed. Usually, the pressure pushed the plug out nicely, but not so with one obstruction, a long lead plug to simulate several bullets stuck in the barrel. Several shots failed to dislodge the plug, but left a distinct bulge in the barrel. Guess where it was? It wasn't at the base of the super heavy lead slug like theory would indicate, it was in the middle! Why? I dunno. I just know that the base upset theory doesn't seem to explain away quite everything yet.
For example, Lyman 311291 linotype slugs that group 3/4" at 50 yards at 2200 fps were tested in hotter loads that were hardly able to stay on target. The best ( control) load gave no leading at all. With two more grains of powder, the bore began to take on a whitish look, and group size almost doubled. With more powder, shooting was wild, and both bore leading and muzzle flashing were severe. Recovered bullets were too damaged to provide definitive information concerning base angles, but the gas check shanks showed little or no sign of a step that should have formed at the edge of the gas check if the base had upset. Miking the top of the gas check shank and lube grooves near the base gave no evidence of any upset, no matter what the power of the load. The biggest difference I found in the recovered bullets was that with the accurate control load, the engraving on the bullets exactly matched the rifling in the bore. Very tiny etched spots were found on the gas check shanks, right at the edge of the gas check itself, where engraving from the lands created a groove.
These spots grew progressively wider and deeper in more powerful loads until they formed a ring around the base of the bullet, between the gas check and the lower band. At the same time, engraving from the rifling on the bullet grew progressively wider by the wearing away of the metal on driving edges of the rifling. On the trailing side of the rifling, the engraving at the gas check began to extend forward to, and through, the driving bands on the body of the bullet. Lead flashing was noted at the muzzle.
There were no obvious differences in the bullet bases or their squareness to the body of the bullet that came anywhere near correlating with the change in accuracy. To correlate the bullet bases with accuracy, going from excellent to wild, the bases would have had to go from almost perfectly square to obviously very crooked. This simply did not happen. It didn't even come close to happening. I don't know that my Linotype bullet bases upset at all. I do know that even if they did upset, it was only very slightly, and not enough to tum my fine accuracy to shotshell patterns. I have deliberately damaged bases far worse and gotten better accuracy. I have done a lot more testing with similar results that I don't have room to relate.
My best guess? I think that in hotter loads, bore leading was deforming my bullets like Dr. Mann's bullets were deformed by his punch mark. But, his punch marks were uniform, so, even though deformed, his bullets were consistent and his accuracy didn't change; he just had to re-set his sights. However, once my bore started leading, it grew worse, becoming more severe with each shot. The leading, as it increased, imparted a different deformation and imbalance to each bullet, and each had a different point of impact!
Now I need to qualify my next statement a bit. Accuracy is a relative term. I'm not a benchrester, and I don't plan to apologize for that, so I use the word "accuracy'' to mean something useful in the field; which could mean groups up to 2.5 moa, depending on what I plan to hunt. That won't take many CBA events, but I shoot a lot more deer and groundhogs than I do matches, and I don't lose any of them from inadequate accuracy. I find that I can get the hunting accuracy I require from hard cast bullets at high velocity.
Why shouldn't I get good results? Col. Harrison's articles in The American Rifleman on paper patched linotype bullets at full power (near 3000 fps) in the .300 Magnum, tell me that linotype is strong enough for high velocities and pressures. If base upset doesn't destroy match accuracy in a 3000 fps loads in a .300 Mag, then it won't cause any major problems at 2600 fps in my '06 either. I may or may not get good results with my '06, but if I don't, it darn sure isn't because the alloy is too soft, and lets the base upset. I need to look elsewhere for the causes of poor accuracy.
I'm beginning to get a handle on where to look for the causes of cast bullet inaccuracy. The paper patches on Col. Harrison's .300 Mag bullets were not for strength, but to prevent bore contact and subsequent leading. We can argue about how it works, but the main thing is that paper patching does prevent leading and permits good accuracy at much higher velocities without gas checks than simple lubes can with gas checks. Note that one of the most remarkable things about my Cream-of Wheat loads is their lack of leading and fouling, combined with high velocity, decent accuracy and a lack of gas checks. Does anyone else see a pattern here?
Many things can cause poor accuracy with cast bullets, including leading, gas check (copper) fouling, poor lube and the like. I'm sure that any base upset that does occur makes its contribution to the accuracy equation, just as any other irregularity will. Base upset unquestionably occurs with soft alloys and hot loads, but I don't think it's the major cause of inaccuracy, and with hard bullets in moderately powerful loads, and I think there's cause to question whether it occurs at all.
Next time, I'll use my myopic magnifying glass to take a look at bullet lubes. Are they really lubricants? If they aren't, what are they? How do they work? Why do they work? Why do we need them at all, and what makes them fail? My ideas may surprise you. See you then. Molly @
Upset in cast bullets has been around a long time. Early experimenters, using muzzle loading rifles, tried many schemes to force undersized balls to expand and take the rifling, but a Frenchman, Captain E. C. Minie had the first real success. Captain Minie employed an iron cup that was driven forward into the hollow base of a conical bullet upon ignition of the powder charge, expanding the base of the bullet to fit the bore. The Minie ball made possible the accurate rifled muskets that could reliably hit individual men hundreds of yards away. Even later, double-rest heavy bench rifles, weighing 20 to 40 pounds, worked best with two-piece swaged lead bullets with bases made of the softest lead to assure expansion. Some men could cut their initials into a 200-yard target with such outfits. That's accurate by any standard! The best rifles and marksmen we have today would be hard put to match it, but, today the expanding base is condemned as a major cause of inaccuracy!
How did expanding bases go from giving the best possible accuracy, to their current reputation for destroying accuracy? Well, to be specific, it is almost entirely the work of one man, Dr. Howard Mann. If you haven't read his book, 'The Bullet's Flight from Powder to Target, you should order a copy right now. Dr. Mann was one of the few truly scientific investigators into the factors affecting accuracy, and his book is still the best on the subject. He was the first to point out that the major cause of poor accuracy is inconsistent bullets. He also found that one of the reasons for inaccurate bullets was the way they upset in the bore. He recovered and measured fired bullets, discovering that the more the base of the bullet is out of square with the body, the further away the bullet will strike from the impact of a bullet with a perfectly square base, and he was right!
Dr. Mann also showed that flaws in the base of the bullet are far more injurious to accuracy than similar flaws in the nose of the bullet. He would drill holes in bullets to duplicate defects and by orienting these defects in the chamber, he could produce large groups like donuts, or he could shoot small groups and move the groups around on the target at will, without changing the sights in any way. Today's shooters equate large groups with damaged bases, and have locked onto the idea that for good accuracy, the base of the bullet must be perfectly formed and perfectly square to the axis of the bullet; but, that's not what Dr. Mann said. He said that the bullet had to be consistent, not perfect. His book shows many examples of fine accuracy with deliberately damaged bullets. He purposely damaged the muzzle of a rifle with a hammer and a punch to prove the point. The punch mark cut a huge groove, from nose to base, in every bullet he fired. This obviously destroyed the balance of the bullet, yet he reported that accuracy was still good; he only had to shift his sights to match a new point of impact.
Dr. Mann believed that the pressure from the burning gunpowder upset the base of the bullet in the throat of the rifle "like a hammer blow on a ball of putty." He tried to prove this by firing bullets from shortened barrels. Some of them were so short that the end of the bullet actually projected out of the muzzle before the trigger was pulled! And brother, did he get upset bases! His bullets looked like opened umbrellas! Even heavy .30 caliber jacketed military bullets were badly upset. The case seemed open and shut: If the pressure of the load is high enough to upset the base of the bullet, it will be unbalanced and inaccurate. Period!
Scuse me, Dr. Mann . . . . Those upset bullets in your photo are a lot bigger than the throat of the rifle. Looks to me like they expanded after they left the throat. Actually, it looks like they didn't expand much until after they got out of the bore altogether ... Oh, I see. It just shows that the pressure in the throat is high enough to make even a jacketed bullet expand as much as it possibly can.
Hmmm. If jacketed bullets expand with high pressures too, why do they shoot so much better than cast bullets. Oh, the softer bullet can't take the pressure as well as the tougher jacketed bullet, and naturally it deforms more and shoots worse? Hmmm. But if jacketed bullets and cast bullets both expand to fit the same throat and the same bore, aren't they deformed exactly the same, no matter what their strength? And, how come you can load a cast bullet to 40,000 psi in an Ml carbine and get good accuracy, but the same bullet isn't worth a hoot at 40,000 psi in a Ml Garand? Won't the amount of upset and accuracy loss be the same in both guns when the deforming pressure is the same? And looky hyar, Doc: Look at these .308 caliber jacketed bullets that I shot in a 7.65 Argentine Mauser. It is obvious that the bullets were rubbing on the lands, but it hardly touched the grooves. If the base upsets completely like you said, why aren't there contact marks all the way around the bullet? And how do boat-tailed bullets make it through the throat without . . . Oww! My ear! No need to be that way about it, Doc! I wuz jest asking!
Like a lot of other shooters, I've done a fair amount of bullet recovery too. I've fired into swimming pools and mountain streams, swimming down to recover the bullets. I've even shot guns completely underwater, much to the dismay of some bluegills. I've recovered bullets from dirt and deer, from wood, sand, snow, sawdust and pretty near everything in between. With low pressure loads or with soft bullets, what I found pretty much goes along with Dr. Mann's findings, even if I do have some questions about the conclusions he drew from the data. But, he dealt mostly with low pressure loads, -the .30-40 Krag was a pretty hot number in his day- and sometimes his results don't translate too well in high pressure and high velocity cast bullet loads.
Oh, Dr. Mann's tests and reports are excellent, and still completely valid; however, we have so deified him, that some people look at a loss of accuracy and jump to the conclusion that they've exceeded the strength of the bullet and are upsetting the bullet base. After all, if Dr. Mann said that is what causes inaccuracy, who are mere mortals to say otherwise?
Well, I have recently read articles by a number of competent people who feel that matching the strength of the bullet to the pressure of the load to get some upset gives them the best accuracy; and don't forget those Minie balls or black powder bench guns. A lot of things can injure accuracy besides base upset. We shouldn't be so quick to assume that poor accuracy means the base is upsetting.
I think it was Gen. Julian Hatcher who reported some tests in which he plugged the bore of a .30-06, and tried to clear it with a case that had the bullet and part of the powder charge removed. Usually, the pressure pushed the plug out nicely, but not so with one obstruction, a long lead plug to simulate several bullets stuck in the barrel. Several shots failed to dislodge the plug, but left a distinct bulge in the barrel. Guess where it was? It wasn't at the base of the super heavy lead slug like theory would indicate, it was in the middle! Why? I dunno. I just know that the base upset theory doesn't seem to explain away quite everything yet.
For example, Lyman 311291 linotype slugs that group 3/4" at 50 yards at 2200 fps were tested in hotter loads that were hardly able to stay on target. The best ( control) load gave no leading at all. With two more grains of powder, the bore began to take on a whitish look, and group size almost doubled. With more powder, shooting was wild, and both bore leading and muzzle flashing were severe. Recovered bullets were too damaged to provide definitive information concerning base angles, but the gas check shanks showed little or no sign of a step that should have formed at the edge of the gas check if the base had upset. Miking the top of the gas check shank and lube grooves near the base gave no evidence of any upset, no matter what the power of the load. The biggest difference I found in the recovered bullets was that with the accurate control load, the engraving on the bullets exactly matched the rifling in the bore. Very tiny etched spots were found on the gas check shanks, right at the edge of the gas check itself, where engraving from the lands created a groove.
These spots grew progressively wider and deeper in more powerful loads until they formed a ring around the base of the bullet, between the gas check and the lower band. At the same time, engraving from the rifling on the bullet grew progressively wider by the wearing away of the metal on driving edges of the rifling. On the trailing side of the rifling, the engraving at the gas check began to extend forward to, and through, the driving bands on the body of the bullet. Lead flashing was noted at the muzzle.
There were no obvious differences in the bullet bases or their squareness to the body of the bullet that came anywhere near correlating with the change in accuracy. To correlate the bullet bases with accuracy, going from excellent to wild, the bases would have had to go from almost perfectly square to obviously very crooked. This simply did not happen. It didn't even come close to happening. I don't know that my Linotype bullet bases upset at all. I do know that even if they did upset, it was only very slightly, and not enough to tum my fine accuracy to shotshell patterns. I have deliberately damaged bases far worse and gotten better accuracy. I have done a lot more testing with similar results that I don't have room to relate.
My best guess? I think that in hotter loads, bore leading was deforming my bullets like Dr. Mann's bullets were deformed by his punch mark. But, his punch marks were uniform, so, even though deformed, his bullets were consistent and his accuracy didn't change; he just had to re-set his sights. However, once my bore started leading, it grew worse, becoming more severe with each shot. The leading, as it increased, imparted a different deformation and imbalance to each bullet, and each had a different point of impact!
Now I need to qualify my next statement a bit. Accuracy is a relative term. I'm not a benchrester, and I don't plan to apologize for that, so I use the word "accuracy'' to mean something useful in the field; which could mean groups up to 2.5 moa, depending on what I plan to hunt. That won't take many CBA events, but I shoot a lot more deer and groundhogs than I do matches, and I don't lose any of them from inadequate accuracy. I find that I can get the hunting accuracy I require from hard cast bullets at high velocity.
Why shouldn't I get good results? Col. Harrison's articles in The American Rifleman on paper patched linotype bullets at full power (near 3000 fps) in the .300 Magnum, tell me that linotype is strong enough for high velocities and pressures. If base upset doesn't destroy match accuracy in a 3000 fps loads in a .300 Mag, then it won't cause any major problems at 2600 fps in my '06 either. I may or may not get good results with my '06, but if I don't, it darn sure isn't because the alloy is too soft, and lets the base upset. I need to look elsewhere for the causes of poor accuracy.
I'm beginning to get a handle on where to look for the causes of cast bullet inaccuracy. The paper patches on Col. Harrison's .300 Mag bullets were not for strength, but to prevent bore contact and subsequent leading. We can argue about how it works, but the main thing is that paper patching does prevent leading and permits good accuracy at much higher velocities without gas checks than simple lubes can with gas checks. Note that one of the most remarkable things about my Cream-of Wheat loads is their lack of leading and fouling, combined with high velocity, decent accuracy and a lack of gas checks. Does anyone else see a pattern here?
Many things can cause poor accuracy with cast bullets, including leading, gas check (copper) fouling, poor lube and the like. I'm sure that any base upset that does occur makes its contribution to the accuracy equation, just as any other irregularity will. Base upset unquestionably occurs with soft alloys and hot loads, but I don't think it's the major cause of inaccuracy, and with hard bullets in moderately powerful loads, and I think there's cause to question whether it occurs at all.
Next time, I'll use my myopic magnifying glass to take a look at bullet lubes. Are they really lubricants? If they aren't, what are they? How do they work? Why do they work? Why do we need them at all, and what makes them fail? My ideas may surprise you. See you then. Molly @