|Table of Contents||
From Ingot to Target: A Cast Bullet Guide for Handgunners©
Leading -- The Cast Bullet Nemesis
In Greek mythology, Nemesis was the goddess of retribution, justice and divine vengeance. She was the daughter of Nyx (the goddess of night), making her the granddaughter of Chaos. She was "the woe of all gods and mortals" and held a deep disdain for excessive pride, boastful or violent behavior, and the absence of moderation. She and her sisters (the Fates) inspired fear due to their vindictive punishment of mortal transgressions. Young Greeks were taught that her wrath was best avoided, and this was done by leading an honorable and humble life, paying homage, and not being proud or boastful. Some stories have the beautiful Nemesis (said to be even more beautiful than Aphrodite) taking the form of a swan and mating with Zeus. From this union an egg was laid, that ultimately delivered Helen of Troy, teaching that even from an angry, vengeful, chaotic force, beautiful things can be born (even though they may be awash in both conflict and controversy, as the rest of Helen's life would be). The parallels to cast bullet shooting are almost poetic. The cast bullet is unleashed upon the world from the chaos and darkness of a revolver's cylinder. Moderation is well tolerated with cast bullets, and excessive behaviors are punished. The wrath of leading is best avoided, and this is easily done, simply by being sensible. Those who pay homage through attention to the details of fit, hardness, lubrication and care of assembly are rewarded with beautiful shooting ammunition (although raucous disbelievers may challenge the virtues of their ammo).
Leading is the number one fear that most non-casters have that prevents them from starting to cast their own bullets. Part of the problem is however, that many of these would-be casters aren't really even sure what "leading" really is, or what causes it; it's just something they've heard, or read, about, and they understand that it can have a negative impact on a gun's accuracy. It is basic human nature to fear the unknown. Some shooters experiment with commercial cast bullets to see how they work and find foreign looking deposits in their barrels and think it must be leading, when in fact it's just residual bullet lube. Sometimes these shooters will experience legitimate leading at intermediate velocities (say 1000 fps or so) and wrongly assume that these deposits would be more severe at higher velocities, and just give up on cast bullets in general. The purpose of this chapter is to define what leading is, what it's root causes are, how a shooter can avoid it, and if afflicted, how a shooter can remove it easily; in short, to dispel the unknown.
Definition of leading. Leading is the deposition of significant amounts of bullet metal on the bore. It can take many forms -- streaks, chunks, splotches, films, etc. (more on this in a minute). It's important to recognize that the mere presence of streaks in the bore is not an indication of leading; many types of bullet lube (especially the commercial hard lubes) leave perfectly innocuous streaks in the barrel that have no negative impact on firearm performance (if a wet patch removes the deposit, it probably wasn't lead). Nor is a gray "haze" on the bore surface necessarily a problem; it can be an indication of a leading problem, but it can also be simply a reflection of the alloy of barrel steel used, how the rifling was cut, or a reflection that the barrel isn't "broken in" yet. The inexperienced cast bullet shooter commonly (and falsely) believes that leading has but a single cause -- the bullet was too soft for the velocity, and lead was stripped off the bullet as it raced down the bore. To this novice shooter, the only solution to leading is to cast the bullet harder, which may solve the problem, but in many cases it won't (and in certain cases it will actually make the leading worse). If the harder bullets don't solve his leading problem, the novice generally walks away thinking that it's impossible to shoot cast bullets without leading a barrel, when in fact the real problem is simply one of misdiagnosis. So let's look at some of the firearm and ammunition issues involved in leading, so our forensic examination of a leaded revolver can provide an accurate diagnosis of the cause.
Location of the leading
Location, location, location! Perhaps the single most telling piece of evidence is the location of the leading in the gun. Are the dark gray, firmly adherent metal deposits in the forcing cone of the revolver, a patch just forward of the forcing cone, random splotches over the central portion of the bore, do they form a light general gray haze of the entire bore, do they specifically "follow the rifling", or are they concentrated near the muzzle? Clues, my dear Watson. The answer is written in the clues.
Throats. Starting from the rear of the revolver and working forward: the first place that leading can appear is in the cylinder throats. This is rare, but it does occasionally happen when the throats are rough or undersized. For example, I have a Ruger SP-101 .22 revolver that used to build up long streaks of lead in the cylinder throats every time I shot it. Turns out the throats were undersized and rough, and a quick regimen of fire-lapping with 600 grit silicon carbide cured the problem nicely. That gun is a nice little shooter now, and no longer leads at all. Another potential cause of leading in the throats is severely oversized throats or undersized bullets, but these extreme dimensional mismatches are rarely encountered today.
Cylinder gap/barrel face. Leading can also be found on the face of the cylinder or the rear face of the barrel. In this case there are multiple possible causes. Most often this is seen in revolvers with an oversized cylinder gap. Ideally a cylinder gap should be between .003" and .006", and most quality production revolvers fall in this range, but every so often one happens across a gun with a gap of as much as .020", and these invariably plate the forcing cone area when shooting lead bullets. Bevel-based bullets are significantly more prone to this kind of leading than are plain-based, for the simple reason that the cylinder seal is broken while there is still a large amount of ablatable lead exposed in the gap, allowing gas-cutting of the beveled face. Seriously oversized throats also can contribute to this form of leading as well.
Forcing cone. Leading found in the forcing cone proper can be the result of the cast bullet being significantly over-sized relative to groove diameter and being swaged down as it enters the forcing cone. It can also be due to the forcing cone being poorly or roughly cut, or cut off-center (it does happen...). Or it can be due to poor cylinder timing leaving the chamber(s) in poor alignment with the barrel at ignition. This last case will generally have an asymmetric build up on one side or the other, and the revolver will commonly "spit lead".
Immediately in front of the forcing cone. If the leading is observed immediately in front of the forcing cone, then it's almost always due to a constriction in the barrel caused by an overly tight barrel/frame thread. This is most readily diagnosed by slugging the bore, and feeling for added resistance as the slug passes through this portion of the bore. Fire-lapping will usually clean this up pretty quickly and effectively. Hand-lapping requires more knowledge and experience, but allows the shooter to feel when the job is done and results in a more uniform bore surface throughout the length of the barrel.
Random splotches in the bore. Perhaps the most commonly observed form of leading is that composed of random splotches of metal throughout the bore. This can be caused by the bullet being too soft for the velocity/pressure (e.g. a bullet with a BHN of 6 being fired at 1100 fps) and it is this single case that has spawned the widespread knee-jerk reaction among the uninformed that all leading is caused the bullet being too soft. Historically, "soft" bullets were cast with 40-to-1 lead to tin (BHN of about 6.5) and "hard" bullets were cast from 10-to-1 (BHN of 11), and if velocities crept much over 1000 fps, it was necessary to be closer to the harder end of the spectrum. Hence, the Oldtimers spoke of the need for "hard" bullets with rounds like the .357 Magnum. They were speaking of bullets with roughly the same hardness as everyday WW alloy (BHN of 10-12), which seems to be considered moderately soft these days. With commercial hard-cast bullets having a BHN of 22 or more and virtually all home-cast bullets falling in the range of BHN 12-18, overly soft bullets are rarely the cause of leading in handguns today (rifles can be a different story).
Random splotches of leading in the bore can also be due to rough or pitted bores. Diagnosis of this problem should be obvious.
These days, random splotches of leading are most commonly due to poor lube flow. This has become a much more common problem over the course of the last decade or so, due to the popularity of the various hard lubes, both on commercial hard-cast and bullets cast at home. Before anyone gets "their tail tied in a knot" over that statement, let me emphasize that this is not meant as a condemnation of commercial hard lubes. A bullet lube must be delivered to the bullet/bore interface for it to do any good. For low pressure loads (e.g. mid-range target loads), hard lube works just fine since the lube displaced by the engraving process of the lands is sufficient to provide for the modest lubrication needs of the bullet in these mild loads. For high-pressure loads (e.g. .44 Magnum), hard lubes also work just fine since the heat and friction of these loads is enough to melt a portion of the lube, and the melted portion of the lube flows extremely well and lubricates the bullet's passage very nicely. Where I have encountered leading with commercial hard lubes is in the intermediate pressure regime, a little over 1000 fps and 20,000 psi. In this regime the lubrication needs of the bullet are not met by the small amount of lube displaced by the lands, and at these more moderate pressures and velocities, little if any of the hard lube melts. A lube that does not flow cannot do its job. In the past, poor lube flow was not an issue because virtually all bullet lubes were soft lubes (e.g. the NRA's Alox formula), and they flowed just fine (in fact, some involving motor oil flowed too well and would leak down and contaminate the powder charge of the round; recall the value of "moderation in all things"). If a shooter is encountering this problem, a quality soft lube is called for.
Streaks, following the rifling. If the leading is seen to "follow the rifling" (i.e. streaks that twist down the barrel in close association with the rifling grooves), then this is a tell-tale sign that the bullet is cast too hard and failing to obturate. Obturation is usually thought of as a plastic deformation that swells the bullet's diameter, but it also leads to a back-filling of engraving defects along the trailing edge of the land. If the bullet is cast too hard to obturate, these defects will not be back-filled and gas-cutting will take place through these voids, following the trailing edge of that particular land. This effect can be mitigated somewhat through judicious choice of lube, but lube by itself can only do so much. The real solution here is to go with a softer bullet and a better lube.
Splotches near the muzzle. If the first half of the revolver barrel is shiny and clean and the lead deposits are only found near the muzzle, then that's a clear indication that the lubrication capacity of the lube/bullet system is being overwhelmed. The shooter has several options to fix this: if the bullet has multiple lube grooves and not all of them were filled, then fill more lube grooves (I know shooters who refuse to fill more than one lube groove on bullets with multiple grease grooves, "Don't wanna waste lube!", I guess they prefer cleaning guns to shooting...). If the bullet has no other lube grooves to fill, then a shooter can move to a more efficient lube, or one with better viscous flow properties. If all else fails, the shooter can go to another bullet design capable of carrying more lube. The problem of muzzle leading is more commonly encountered in rifles than it is in handguns.
General haze over the entire bore. If the lead deposits show up as a gray haze over the entire bore it may not be an indication of a leading problem. Sometimes this is just an indication that a barrel still needs to be broken in. The way some barrel steels behave when cut, there can be microscopic surface roughness that accumulates a fine-grained film of lead over the surface for the first few hundred rounds or so (this used to be particularly common with stainless revolvers, especially Rugers, but the situation has improved in recent years). If this haze bothers you and you want it to go away, just go out and shoot then gun, alot! If you're impatient, then fire-lap it.
If the haze is more than just a fine-grained, light gray haze, and amounts to more serious leading over the entire bore, it is most likely due to the cast bullets being undersized relative to groove diameter. Slug the barrel and throats and make sure that the throats are indeed larger than groove diameter, and that the bullets are sized at least as large as groove diameter.
Causes of Leading
Now that we've seen what leading looks like, and have some idea as to where it's coming from, let's look at the different factors that cause leading and what we can do to eliminate it. In other words, let's look at it from the other side of the fence and start with the cause and work backwards.
Leading caused by the bullet. The cause of leading can be traced to the bullet if it's the wrong hardness for the application, the wrong size for that particular gun or a plain base design in an application that calls for a gas-check. As discussed above, too soft of a bullet (e.g. BHN < 8) can be stripped if pushed too fast, while a bullet that's too hard (e.g. BHN 22) can fail to obturate, and lead the trailing edge of the lands. This is a common problem with commercial hardcast bullets pushed at intermediate velocities. The bullet can also be the source of leading if it is sized too large (lead build up in the forcing cone) or too small (coated over the entire bore). The bullet can also be the cause of leading if the sixgunner is using a PB bullet in a load that generates more than about 40,000 psi peak pressure or 1500 fps muzzle velocity; these applications are better served by GC bullet designs.
Leading caused by the lube. Lube can also be the cause of leading, either by there not being enough of it on the bullet, or by having poor lubricating abilities, or by having inadequate viscous flow properties. The tell-tale signature of a bullet running out of lube is leading concentrated up near the muzzle. The solution here is to go to a thicker lube or a bullet design with more lube capacity. Make sure that your bullet carries enough grease, and that you put good stuff in those grooves. Soft lubes (e.g. NRA's Alox formulation) are much more versatile, hard lubes work well for soft loads and magnum loads, but can be problematic in between.
Leading caused by the gun. There are certain critical dimensions of the gun that can cause leading if they are "out of spec". Again, starting with the rear of the gun and moving forward, the first of these would be the cylinder throats. If the throats are grossly oversized (.004" larger than groove diameter) then if the cast bullet is soft enough it can "bump up" when fired, becoming oversized for entry into the forcing cone, creating lead deposits when it gets swaged back down at this point. With harder bullets, oversized throats do not usually cause a leading problem (although accuracy may suffer due to poor alignment during the cylinder gap transition). On the small side, tight throats can be more problematic. If the throat diameter is .001" (or less) under groove diameter, poor accuracy and serious leading are commonly the result since the cast bullet gets swaged down too small and rattles down the bore with poor alignment allowing lots of gas leakage. Fortunately, this is an easy problem to fix, just hone (or polish) the throats to the proper diameter. It's important to recognize that not all revolvers with tight throats will necessarily shoot poorly, or lead the bore (tight throats coupled with the right amount of barrel constriction will often shoot just fine with moderate pressure loads), but the general trend is that tight throats are usually problematic.
If the barrel/cylinder gap is excessive (.010") then the forcing cone area can become plated with lead deposits. This is fairly common with .22 revolvers, but is also occasionally seen in centerfire revolvers as well. The solution here is to have a gunsmith set the barrel back one thread and re-cut the barrel face so that the gap is more reasonable (say .004-.005").
Perhaps the most common cause of leading that can be blamed on the revolver is the barrel/frame constriction. Sometimes, when the manufacturer cuts the threads on the barrel and screws it into the frame, it's a tight enough fit that the frame slightly constricts the barrel so that the groove diameter in that portion of the barrel is ever so slightly smaller than in the rest of the barrel (the difference is usually less than .001"). The crude swaging process that occurs when a bullet is fired generally results in a heavy lead deposit at the barrel frame juncture. Fire-lapping (or hand-lapping) will generally cure this problem in straightforward fashion.
Variations in steel hardness or slippage in the indexing of the cutting tools when the rifling grooves were cut the barrel can be left with inconsistent groove diameter, or groove/land widths, or tool chatter leading to a roughly cut bore. All of these inconsistencies can be treated with some degree of success by fire-lapping or hand-lapping. Likewise a bore that has become pitted can also be smoothed out in this fashion (but only up to a point). Note that most of the gun related causes of leading are “treatable” by fire-lapping.
Leading caused by the load/components. Perhaps the most common source of leading resulting from the components is due to the use of too little, or inappropriate, bullet lube. Some bullet designs have skimpy little shallow lube grooves and simply do not carry enough lube to be shot at any kind of serious velocity without leading. These bullets will never provide satisfactory service at anything other than moderate velocities. Lube quality is a little muddier issue; one of the things that confuses many cast bullet shooters is that a lube can be very well suited for one velocity range and lousy at another speed. A common (and somewhat shaky) belief is that a given lube will be good up to a certain velocity (at which point it will reach the limit of its lubricating/sealing ability), therefore if it works at one velocity it will work fine at all velocities below that point. This is commonly true, especially for the soft lubes (also the varnish lubes and dry Moly coatings), but not always true for the hard lubes (particularly the crystalline hard lubes). If you're getting leading that you can trace to the use of a hard lube, try replacing it with a quality soft lube.
Another source of leading that can be traced to the components of the load is the mismatch of the powder burn rate to pressure generated by the load. Many years ago Elmer Keith used to write about the "balance point" of a given powder; the range of pressures at which that powder delivered smooth uniform ballistics. Basically this boiled down to fast powders for light target loads (e.g. Bullseye, W231, HP-38, AA #2), medium burners for standard pressure loads (like Unique, Universal Clays, AA #5), medium slow powders for +P loads (powders like HS-7, Blue Dot, AA #7) and slow powders for full-house magnum loads (like W296, H110, 2400 and AA #9). Match the powder to the pressure curve. The use of fast powders for higher than normal pressures with plain-based bullets can cause bad leading, due to the very rapid pressure rise time early in the P-T curve leading to high pressure faster than the bullet alloy can obturate in response to the pressure, and as a result severe gas cutting can result. The other issue here is that the slow pistol powders reach their pressure peak when the bullet is an inch or two in front of the forcing cone, when the bullet is fully supported and contained by the barrel. Sealing and lubrication are fully functional in this environment. The fast pistol powders reach their peak pressure when the bullet is in the throat or traversing the cylinder gap. This is fine if the load involves modest pressures, but if a plain-based cast bullet is subjected to magnum pressures as it crosses the cylinder gap, then serious leading problems can arise. The take-home lesson here is to not use fast powders for magnum pressure levels in the first place! Just match the powder to the pressure curve.
The bottom line of all this analysis? Use a bullet that's the right size, of a hardness suitable for the pressure/velocity, with a healthy dose of quality lube, in a decent gun, powered by a well-balanced powder charge, and you'll be able to shoot all day long with no leading. It's really pretty easy, all told.
Removal of leading
The default method for removing lead deposits is a bronze bore brush, a healthy dose of elbow grease and an hour of two of scrubbing. If your time is as valuable to you as mine is to me, this is not a good solution!
One solution that gets recommended is to fire a couple of rounds of jacketed ammo to clean up majority of leading deposits -- in my experience jacketed ammo tends to remove most, but not necessarily all of the lead (it seems to iron some of it into the grooves since jacketed bullets tend to be slightly undersized). Some have even gone so far as to suggest loading jacketed bullet upside-down to enhance the scraping effect -- I've never done this, but it seems rather odd to me, all you need is the harder jacket metal in contact with the leaded bore so what purpose does loading the bullet upside-down accomplish? And if the jacketed bullet is undersized it won't make any difference whether it's right side up or upside-down. The best solution I've found yet, is to simply shoot some GC ammo through the leaded bore. The sharp forward edge of a GC seems to do a much better job of removing lead deposits than a typical bullet jacket, and I can't think of a better way to clean a gun than to keep shootin'!
What if you don't have any GC ammo handy? Well then, there are a few other options....
Veral Smith, of Lead Bullet Technologies (LBT), published a method in his excellent (and highly recommended) book Jacketed Performance from Cast, a nifty and highly effective method for removing lead deposits from inside a barrel. His method involves taking a copper or brass kitchen scrubbing pad (commonly marketed under the "Chore-Boy" or Chore-Girl" brand names) and cutting a patch off of it and wrapping it around a bronze bore brush. The way this "tool" cuts through even severe lead deposits has to be seen to be believed! I have had revolvers that I literally could not even see the lands that came clean and lead free in less than a minute!
The only drawback to Veral's method is that it requires a pair of scissors to slice off a patch of the scrubbing pad, and scissor slicing launches a thousand little pieces of shrapnel off into the unknown (at least its unknown until you walk back through that particular room barefoot), and it only allows you to get a dozen or so swatches out of one scrubber pad. If one replaces the copper (bronze) kitchen scrubbing pad with a pad of bronze wool (available for refinishing work at your local hardware store), one can take a small pinch off the pad with your fingers and get about a hundred or so pinches from one pad -- and there's no mystery shrapnel to stab your (or your Better Half's) tender tootsies! It's important to emphasize that one should use bronze wool, and not steel wool. Steel wool will scratch the bore, and why a shooter would want to save a few cents and use steel wool instead of bronze wool and risk damaging several hundred dollars worth of barrel is beyond me when he could just as easily buy a cheap cleaning accessory where a $3 investment will last the next couple of decades with zero risk to his precious barrel steel. Your call...
Shooting bullets lubed with Moly lube not only prevents leading, but also makes lead deposits easier to remove when they do occur. This is the one case where a wet patch can remove light leading deposits, they don't stick very well and good tight-fitting patch wrapped around a bore brush can remove leading deposits from a lightly leaded barrel if that barrel is Moly treated.
So look at the variables involved with your gun -- bullet diameter, bullet hardness, throat diameter, groove diameter, lube quantity and quality, possible barrel constrictions, bore roughness, cylinder gap, etc. Gentle fire-lapping can cure several, but not all, of the causes of leading. It may very well be that your gun just needs to be broken in, so just get out and go shootin'!
Fear of barrel leading is one of the greatest barriers to shooters taking up cast bullet shooting and bullet casting. In the final analysis, leading is easy to avoid, and it is much easier (and quicker) to get rid of than is copper fouling from shooting jacketed bullets. That a cast bullet shooter must live with leading is a myth, just like Nemesis of ancient Greece.
|Table of Contents||Continue to Chapter 8 - Idle Musings of a Greybeard Caster|
|Index of Additional Glen E. Fryxell Shooting Articles|