Alloy Hardness terminology

[SniderBoomer]

I sometimes read articles referring to alloys that are "twice as hard as alloy-x"

Got me thinking, what is the actual way to describe hardness in multiples like that?

E.g, is a BNH 16 alloy twice as hard as BHN 14, or (as I have been assuming) 'two points harder' on the BHN scale?

Not anything to lose any sleep over I know...

[Larry Gibson]

With cast bullet alloys the BHN is only half of the story. The other half is the malleability of the alloy. We can easily have two different alloys of the same BHN, one brittle and one malleable. For example; linotype generally has a BHN of 22-24. Linotype is brittle and many times will shatter on harder targets like bone. COWWs + 2% tin mixed at 50/50 with lead and WQ'd will also have a BHN of about 22-24. However it is more malleable and will expand and hold together better through the same bone.

Thus it is not really applicable with different cast bullet alloys to compare their BHNs in a linear fashion. It gets done all the time though but it is not entirely correct and can be misleading most of the time.

Larry Gibson

[SniderBoomer]

Great reply Larry

[Harry O]

I think the question and the answer are talking about two different things.

Brinell is linear. A Bhn of 10 is twice as hard as a Bhn of 5. A Bhn of 20 is twice as hard as a Bhn of 10 and four times as hard as a Bhn of 5.

How that hardness reacts in a barrel is somewhat different depending on what the mix is. With two equal hardnesses, one with lead/antimony and one with lead/tin, the one with tin will go to higher velocities than the one with antimony (given everything else equal) before leading occurs. However, the mix with tin will cost much more than the mix with antimony. You need a lot of expensive tin to equal the hardness of a little bit of antimony.

Tin seems to increase the hardness in a fairly linear fashion in low percentages (about 1 Bhn for each 1% increase in tin), but it rapidly gets less effective when larger amounts are added. Antimony seems to increase the hardness with much smaller percentages and it increases hardness much faster than tin. Antimony also gets less effective when larger amounts are added (it does not seem to increase the hardness much after about 16% to 18%), but it goes to much harder mixes before it peters out than tin does. These are just based on my observations (and tests), and I know that lots of people have lots of different opinions.

The best for me is a combination of antimony and tin. Relatively small amounts of antimony gets the bullet to much harder than I can do with tin alone. However, tin is needed to make it ductile and keep it from shattering. It also makes the mix easier to cast with. I try to use about as much tin as I have antimony, but I know many others can get by with half as much tin as antimony. I have done that, but it is a lot easier for me to cast with equal amounts.