Hardness, Leading Issues And Other BS
Part 1 - Optimal Hardness
The use of BHN numbers
has become a standard among consumers to compare and contrast cast bullets from
various manufacturers to quantify the differences among the various cast bullets
available to the consumer.
Supposedly by understanding how hard a bullet is, the consumer can then select the right hardness for his or her particular shooting application.
I donít as rule like using BHN numbers and when customers call asking for the BHN numbers of our bullets I want to take way more time to explain what they need to know rather than what they think they need to know.
The problem is that BHN is only one measured aspect of a cast bullets alloy. Not understanding what that number really means or what it signifies is really meaningless. Some have offered pressure equations that allow one to determine the amount of hardness needed for a particular load and a given velocity so the consumer feels he has chosen the optimal bullet for his needs. These equations show how much pressure is needed to make the bullet base expand (obturate) in order for the bullet to fill the lands and grooves of a barrel.
Such a need was required in the old days especially with old black powder rifles and pistols and barrel dimensions that were far from being exact and consistent from gun maker to gun maker. Even barrels made by the same maker had wildly different tolerances.
Itís kind of funny that despite the vast improvements in CNC machining technology that we still find wide variance even today in some guns. For example, I like to pick on Ruger as one of those companies that has produced great guns but also has given us some horrible dimensions in those guns. Older .45 Colt guns had cylinder throats that would routinely measure in the plus .455" - .457" range (I know as I have one). At the same time the current versions of that gun are running cylinder measurements of .451" (I have one of those too) and then over a period of time the cylinders went to .454" as reported by customers who bought later versions of the Vaquero. Recently in the last few months there were two S&W revolvers that had cylinder throats at .432" and that is rare as most of the S&W revolvers in .44 mag. were just fine at .430" on the cylinder throats. By the same token the Rugers and the S&W guns have been fairly good on barrel dimensions with most coming in at standard specs for a given caliber. Colt Pythons have had some of the tightest barrel dimensions that I have measured at .354".
The point is that within a range the tolerances have been somewhat consistent thru the runs of these guns with most of the variations coming in the cylinder throats. Now once those dimensions are known for your particular gun then the issue of getting bullets of a proper fit is relatively easy. Once you get bullets of a proper fit then obturation no longer becomes necessary to get an effective seal. If the bullet is at or over the largest dimension then the bullet will swage down and seal and make a perfect fit. The only time this becomes a problem is if the throat dimensions are off by a large margin of more than .002"-.003" over the barrel dimensions. Much more than that can cause the bullet to strip away within the barrel leaving long strings of leading down the barrel.
Now what does this have to do with BHN numbers? Glad you asked.
BHN numbers only tell you how hard something is period. It tells you nothing about Alloy Strength. I can easily show you two bullets that will both measure for all intents and purposes the same BHN numbers but be wildly different in the alloy composition. One will be hard and brittle with high exposure of antimony in the mix and very prone to lead fouling while the other with an equally high number will be much stronger and far more ductile in its strength.
The standard 2/6 alloy (2% tin, 6 % antimony) as developed by Taracorp wasnít developed for its performance characteristics as a cast bullet alloy but rather its performance as an alloy that would pour and run well in automatic casting machines that produced cast lead bullets.
The 2/6 alloy proved to be a good alloy for a range of shooting applications but also had problems of being too hard and brittle for some applications and not strong enough for other applications.
Let us take a look at two other alloys. Linotype which is a 4/12 mix (4% Tin, 12% antimony and the balance lead) that is also known as a eutectic alloy. This simply means that this alloy at these ratios will melt and solidify at the same temperature. The alloy is hard and strong and measures about 21-22 on the BHN scale. It was the standard alloy as used in old line-o-type machines as used by printers and newspapers all over the world. Great stuff but itís almost non-existent in the
The alloy in straight form was usually too hard for most cast bullet users except for rifle use where its performance up to 2100 fps could be had without the need for gas checks on the base of the bullets.
Most casters would use type metal for hardening a supply of softer lead and in the beginning this was the method I used to produce my own alloys and still use some of these materials to this day as much as the supply of those items will permit.
The other alloy is Lymanís No. 2 alloy which Lyman developed many years ago. It is essentially a 5/5 alloy with a 5% tin and 5% antimony mix, balance lead. This alloy which is expensive to produce in large quantities found a home with the hobbyist bullet caster as its performance was very good. This one to one ratio provided an alloy that while it did not measure as high as the 2/6 alloy on the BHN scale had the advantage of being almost as strong as the linotype alloy (4/12).
Thatís why I tell people not to get hung up on BHN numbers because they canít tell you the whole story and using them as a comparison between cast bullet brands is pretty much worthless without having all the information at your disposal.
The advantage that I have is that by having my own foundry and mixing my own metals for my own use in my products is that I have total control over the QUALITY and STRENGTH of the alloys that I use.
The alloys that I offer because of their high strength are more adaptable and usable over a much wider range of loads and velocities than other casters that buy and use the standard 2/6 mix.
Thank you for letting me be of service to you,
Bob Palermo / President. firstname.lastname@example.org
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