Excerpt from Fouling Shot 129, Ken Mollohan
In previous issues of The Cast Bullet I've discussed my thoughts on bullet lubes and explained why I believe they improve performance by keeping powder fouling soft and by wetting the bore to prevent molten lead from soldering to the steel. Regardless of the cause of leading, it is generally agreed that it is the kiss of death for accurate shooting.
Many things can cause the accuracy of castbullets to fall off. Small losses, of half an inch or so, in grouping abilitycan be caused by anything from a stock warping, to variations in age hardeningof the bullet causing differences in base upset and obturation; but in verypowerful cast bullet loads, loss of accuracy is usually more the base of the bullet and the walls of the throat and bore and the cereal acts like a plug, preventing gas from blowing past the bullet. The COW plug minimizes leading and delivers a better bullet at the same time. In addition to sealing off hot gases, the COW performs a second function, sweeping the bore clean of any powder fouling and traces of lead. In a good load, using a sufficient amount of COW, the bore remains bright, clean, and shiny, shot after shot, resulting in more consistent accuracy.
I know someone will protest that leading iscaused by the alloy rubbing off the bullet onto the steel, not by etching fromhot powder gases. I used to think so too, but one day I realized that some airrifles can shoot thousands of unlubricated lead pellets at velocities over 1000 fps without accumulating lead fouling. Why doesn't lead rub offin their bores?
In previous issues of The Cast Bullet I've discussed my thoughts on bullet lubes and explained why I believe they improve performance by keeping powder fouling soft and by wetting the bore to prevent molten lead from soldering to the steel. Regardless of the cause of leading, it is generally agreed that it is the kiss of death for accurate shooting.
Many things can cause the accuracy of castbullets to fall off. Small losses, of half an inch or so, in grouping abilitycan be caused by anything from a stock warping, to variations in age hardeningof the bullet causing differences in base upset and obturation; but in verypowerful cast bullet loads, loss of accuracy is usually more the base of the bullet and the walls of the throat and bore and the cereal acts like a plug, preventing gas from blowing past the bullet. The COW plug minimizes leading and delivers a better bullet at the same time. In addition to sealing off hot gases, the COW performs a second function, sweeping the bore clean of any powder fouling and traces of lead. In a good load, using a sufficient amount of COW, the bore remains bright, clean, and shiny, shot after shot, resulting in more consistent accuracy.
I know someone will protest that leading iscaused by the alloy rubbing off the bullet onto the steel, not by etching fromhot powder gases. I used to think so too, but one day I realized that some airrifles can shoot thousands of unlubricated lead pellets at velocities over 1000 fps without accumulating lead fouling. Why doesn't lead rub offin their bores?
I decided to find out just what it takes to make a lead alloy stick to clean steel I tried rubbing lead and steel together by hand, smashing them together with a hammer, compressing them in an hydraulic press, spinning them against each other in a hand drill, and shooting lead bullets at a steel backstop. I tried high and low percentages of tin. I could only produce a slight smear of alloy on the steel, and I could wipe that off with my thumb
.
Nothing I conjured up produced any buildup on the steel unless I managed to melt the lead alloy in the process. I finally loaded .22 caliber air rifle pellets in .222 cases and shot them at velocities ranging from 800 fps to 1000 fps. In all but the lightest loads, the pellets leaded the bore like you simply wouldn't believe. The base of the recovered pellets looked like they had been sandblasted but I didn't see any evidence of melting. An air gun uses relatively cold air to push the lead pellet down the bore, but a firearm uses hot gas with a flame that can be above the melting point of steel. I tied this together with the fact that I couldn't get lead to stick to steel without melting it and concluded that the difference between the air rifle and my .222 loads was etching of microscopic molten droplets of lead from the pellets by the hot powder gas.
.Nothing I conjured up produced any buildup on the steel unless I managed to melt the lead alloy in the process. I finally loaded .22 caliber air rifle pellets in .222 cases and shot them at velocities ranging from 800 fps to 1000 fps. In all but the lightest loads, the pellets leaded the bore like you simply wouldn't believe. The base of the recovered pellets looked like they had been sandblasted but I didn't see any evidence of melting. An air gun uses relatively cold air to push the lead pellet down the bore, but a firearm uses hot gas with a flame that can be above the melting point of steel. I tied this together with the fact that I couldn't get lead to stick to steel without melting it and concluded that the difference between the air rifle and my .222 loads was etching of microscopic molten droplets of lead from the pellets by the hot powder gas.
Another generally accepted and seemingly reasonable theory claims that smooth barrels work best with cast bullets because rough bores abrade a cast bullet like a file leaving lead in the bore. Some lead may indeed be abraded off a bullet fired in a rough bore, but, if so, the bore irregularities should be constant from shot to shot resulting in uniform bullet deformation from shot to shot, and accuracy should not be greatly affected.
.Even if some alloy is rubbed off the bullet, what makes it stick to the bore? My tests indicate that it must melt to adhere. I believe that rough spots in the bore deform the bullet, engraving small grooves on its surface. Once past the roughness, these grooves allow gas to escape past the bullet, etching it and causing much more leading than you would get in a smoother barrel Incidentally, I think this may be why fouling from jacketed bullets is so hard on ordinary cast bullets. I believe that very hard, irregular jacketed fouling causes lead fouling just like a rough bore. In my experience even the roughest bores are capable of reasonable accuracy if the loads, and therefore the gas temperatures, are kept mild enough Cream Of Wheat filler loads are not very sensitive to jacketed fouling, probably because the gas can't get through the grooves that the copper fouling leaves on the bullets
There are some well known tricks to get decent accuracy with high power cast bullet loads. Seating the bullet into the barrel throat not only gives better alignment with the bore, but also minimizes the flow of gas around the bullet Using a slow burning powder is also advantageous; slower powders burn cooler and less heat means less etching. Paper patching bullets to protect them against gases also works. Even a single copper cup at the base provides a substantial improvement over the velocity potential of plain based cast bullets.
Notice how many of the things that improve shooting with high power cast bullet loads can be explained from the perspective of lead etching by the hot powder gases. Virtually everything that helps maintain accuracy at high velocities, prevents or minimizes etching. This forces me to conclude that etching and the resultant bore leading are at least among, if not the primary causes of catastrophic accuracy loss in high power cast bullets. Whether you believe the gas just softens the surface of the bullet, or the blow-by etches it, is immaterial. In truth, it may be impossible to separate the two theories, because etching cannot occur unless the surface of the bullet is heated sufficiently to result in serious softening of the alloy. The point to remember is that accurate high velocity cast bullet loads are made possible by either paper patching or COW filler.
While smokeless powders permitted improved power with jacketed bullets, their much hotter flame caused cast bullets to go into a low performance slump for generations. We now stand ready to pull cast bullets out of that slump with loads yielding little or nothing to their jacketed descendants in terms of power or accuracy. The many confirmed successes with high power cast bullets prove that good accuracy is possible though not yet as readily obtained as with jacketed bullets. I confidently expect cast bullets to resume their traditional role of providing inexpensive shooting of the finest accuracy but at power levels as high as modern ammunition can deliver. I do not think cast bullets are likely to displace jacketed bullets, but only because cast bullets are the products of individual effort and not well suited to commercial production
.
Now it's your turn. What kind of objections tomy ideas can you think of? What did I overlook? What did I misconstrue? Whathave you seen that I haven't seen? Believe it or not, I really hope someone canshoot me down in flames because that will give me a chance to work out othertheories, besides, I love armchair ballistics almost as much as actualshooting. So come on, all you brother armchair ballisticians, have at it!
There are some well known tricks to get decent accuracy with high power cast bullet loads. Seating the bullet into the barrel throat not only gives better alignment with the bore, but also minimizes the flow of gas around the bullet Using a slow burning powder is also advantageous; slower powders burn cooler and less heat means less etching. Paper patching bullets to protect them against gases also works. Even a single copper cup at the base provides a substantial improvement over the velocity potential of plain based cast bullets.
Notice how many of the things that improve shooting with high power cast bullet loads can be explained from the perspective of lead etching by the hot powder gases. Virtually everything that helps maintain accuracy at high velocities, prevents or minimizes etching. This forces me to conclude that etching and the resultant bore leading are at least among, if not the primary causes of catastrophic accuracy loss in high power cast bullets. Whether you believe the gas just softens the surface of the bullet, or the blow-by etches it, is immaterial. In truth, it may be impossible to separate the two theories, because etching cannot occur unless the surface of the bullet is heated sufficiently to result in serious softening of the alloy. The point to remember is that accurate high velocity cast bullet loads are made possible by either paper patching or COW filler.
While smokeless powders permitted improved power with jacketed bullets, their much hotter flame caused cast bullets to go into a low performance slump for generations. We now stand ready to pull cast bullets out of that slump with loads yielding little or nothing to their jacketed descendants in terms of power or accuracy. The many confirmed successes with high power cast bullets prove that good accuracy is possible though not yet as readily obtained as with jacketed bullets. I confidently expect cast bullets to resume their traditional role of providing inexpensive shooting of the finest accuracy but at power levels as high as modern ammunition can deliver. I do not think cast bullets are likely to displace jacketed bullets, but only because cast bullets are the products of individual effort and not well suited to commercial production
.Now it's your turn. What kind of objections tomy ideas can you think of? What did I overlook? What did I misconstrue? Whathave you seen that I haven't seen? Believe it or not, I really hope someone canshoot me down in flames because that will give me a chance to work out othertheories, besides, I love armchair ballistics almost as much as actualshooting. So come on, all you brother armchair ballisticians, have at it!
