Toughness Of Lead-tin-antimony Alloys

[MakeMineA10mm]

Thanks Grumpy. It all makes pretty good sense to me, now that I've re-read it and you've responded to my questions. I agree with most everything you say, especially about people making their boolits too hard.

I found what is probably the same article by Dennis Marshall in the Lyman Cast Bullet Handbook. It's about a 12 or 13 page article which goes into a lot of scientific analysis of lead and lead alloys. Talks about binary & ternary alloys, metallic solutions, etc. More light reading!

[azduke]

Reading this is very interesting and makes one do some thinking.I'm new to this and am trying to learn as much as I can.Planning on casting my own when I get my project rifle put together.Was planning on using the wheel weights I have stockpiled as a basis,but according to an nra contributing writer wheel weights are to "hard" for round ball and black powder cartridge bulletts

[yodar]

Do you equate ductility with ability to obdurate?

Yodar

[grumpy one]

Do you equate ductility with ability to obdurate?

Yodar

Ductility is the extent to which a material can be deformed plastically without fracture. Thus it is extremely high for pure lead, and extremely low for most type-metals. It seems to me that this is closely related to, say, a plug's potential to be expanded permanently in diameter without cracking, by squeezing it axially. In other words, ductility should be a measure of the extent to which a bullet is capable of obturating without cracking. However it does not relate to the pressure required to make it obturate, although many shooters probably treat these two considerations as closely related. There are some more subtle factors that come into the picture too: for some materials ductility in tension and compression may be different.

[Marlin Junky]

Maybe someone has already addressed this point, but how do the larger diameter boolits respond to the toughness testing? Would you be willing to repeat the tests with .375 cal boolits? I'm sorry I didn't have time to carefully read everything, but what were your casting conditions?

MJ

[grumpy one]

Maybe someone has already addressed this point, but how do the larger diameter boolits respond to the toughness testing? Would you be willing to repeat the tests with .375 cal boolits? I'm sorry I didn't have time to carefully read everything, but what were your casting conditions?

MJ

There are two issues with larger diameter bullets - one test-related, the other metallurgy-related. The test-related issue I've discussed above: the length to diameter ratio of the bullet is important. Short fat bullets are unsuitable for transverse fracture testing. In addition there is a scale issue: the actual impact energy measurement would increase with bullet diameter, so it would be necessary to repeat the entire series of experiments, on all alloys, for each calibre. Just as the Charpy and Izod tests use a single, arbitrary specimen size to represent an alloy, I have used 30 calibre and am continuing to do so in the follow-up experiments. I do not think repeating the entire series with a different calibre would add anything to the science content of the work, except in relation to the metallurgy-related issue.

The metallurgy-related issue has been raised by several people in the discussion above and elsewhere on this board: since the quenching process removes heat only via the exterior of the bullet, the surface-to-volume ratio will influence how quickly the core of the bullet cools. Most likely large calibre bullets will show more variation in hardness from surface-to-core than will small calibre bullets. This is a subject that might be worth investigating, but not as part of a series of experiments aimed at researching toughness.

I've set out most of the details of casting conditions in the report, and supplemented it to some extent in the discussion above. I haven't mentioned that I generally followed my standard approach to casting: start with a metal temperature of 750 F until the mould warms up and the bullets become frosty, then wind back to 650 F. I use a lower temperature than 650 F for most moulds, but this series of experiments uses 311466, which is a Loverin design. My experience has been that I need perhaps 50 F higher casting temperature for this (Lyman DC) mould than I do for two-groove 30 calibre designs such as 311291. Conversely, the little 311255 is so easy to cast I use an even lower temperature - typically less than 600 F. The bullets were dropped onto a towel and air cooled, then heat-treated at a later date.