Exactly what benefits are claimed from using “hard cast” bullets? It just struck me as being simply meaningless advertising babble, but I never was interested enough to look into it
I've been casting my own bullets since 1972 and spent a lot of time and effort studying the works of Col. E.H. Harrison (Cast Bullets, an NRA publication) and others. Perhaps I can provide some perspective on the subject of "hard cast".
Lead is a relatively soft and malleable elemental metal. In the pure state lead will melt at about 650F and can easily be indented or scored with a fingernail. On the Brinell Hardness Scale pure lead has a rating of 7-8.
By the late 19th Century many shooters were adding small percentages of tin (from 2-10 percent) to their casting lead. When alloyed with lead the tin improves fluidity in the metal, providing cleaner and more detailed casting results, while also raising the Brinell hardness rating to about 10-12. A disadvantage to this practice is the cost of tin, which is easily 10 times the cost of lead.
Printers used block printing presses for many years, wooden frameworks with lines of print made of cast lead alloys, providing repeated uses to reproduce printed materials quickly and inexpensively. The alloys used included linotype and monotype, which contain lead alloyed with tin and antimony (also tiny percentages of arsenic) resulting in Brinell hardness ratings from 20-30 (2.5 to 4 times the rating of pure lead).
Reloaders and bullet casters found that linotype and other printing metals were widely available in most communities and could be used in casting bullets for higher performance than pure lead (either by themselves or when alloyed with lead for less demanding applications).
Automobiles became widely used in the US by the WW2 years, and wheel balancing was routinely done using wheel weights attaching to the wheel rims. Wheel weight metal was an alloy of lead, tin, and antimony with a Brinell hardness rating of about 12. This proved just about ideal for use in handguns in general, as well as many rifle calibers.
Adding hardness using tin and antimony produces some useful effects for our purposes:
1. Increased resistance to melting of the bullet bases due to powder flame temperatures. Such melting can cause smearing of the bore and splattering of other surfaces (widely referred to as "leading", a condition that requires greater efforts to keep the firearm clean and operable).
2. An associated benefit with increased melting resistance is found as the bullet passes through the bore and rifling, where the temperatures caused by friction increase as velocities are increased. Short version, harder bullets can be pushed faster than softer pure lead without the concerns of lead transferring or depositing in the bore and rifling.
3. Increased resistance to distortion, both during the firing cycle as rapidly rising pressures are applied to the bullet, as well as when striking a target where the softer lead bullets tend to upset more so than the hardened lead alloy bullets.
I could add a chapter or two about bullet lubricants, but the above outlines the basics.
Like everything else, there are compromises to be made. Soft lead bullets upset and expand more readily and at lower impact velocities/energies, thus are less likely to penetrate deeply and can cause increased soft tissue damage. Harder bullets can be expected to penetrate more easily, travel deeper in the target, and usually better performance against solid materials such as bone or barrier materials. However, hardness above a certain level can also cause cast bullets to become excessively brittle and potentially shatter when impacting solid materials.
For firearm uses pure lead bullets are generally limited to around 800-850FPS before leading can become an issue. At such velocities even pure lead will seldom demonstrate much distortion upon impact, and penetration will be limited to the energy levels.
Bullets in the range of BHN 12-15 (wheel weights and harder) can be delivered at velocities in the 1400-1500FPS range without much difficulty, thus double the velocities and about 4 times the energy of pure lead bullet loads.
I have personally had success with cast bullets in centerfire rifles at velocities at or slightly above 2500 FPS using alloys in the range of BHN 20-24 (also gas checks, which is another subject to be considered). This provides useful performance comparable to service loads in .30-06, and far exceeds the .30-30 cartridge.
Hope this helps in understanding how "hard cast" came into common use. There is no universal definition of the term, but it is understood to mean bullets produced with alloys providing greater strength and resistance to slumping (deformation) and temperatures.
