LEad alloys and age hardening.

[ffffgdave@yahoo.com]

Finnaly something i can add to the black powder list.. i bought a series of books from the nra probably 15 to 25 years ago for info on boar leading and all kinds of stuff. here (amung hundreds and hundreds of articles in four books) is a very interesting article that many here have asked me about.. the book is cast bullets by col e h harrison a publication by the national rifle assosiation.. c0py right 1979. reprinted from past articles of the american rifleman.. i think col e h harrison was the question and answer guy back then.. (these books have some really amazing stuff... )

question: it seems to me that cast bullets become harder upon standing, please explain.........

col harrison replies. your observasion is correct. lead alloys do harden considerbly for a time after casting (spontanious hardneing is ment here not that from heat treatment. ). this has had almost no mention in the cast bullet information and the misinformation published to handloaders for generations. it is remarkable that something which can greatly affect bullet performance. and which is observable and measurable with simple means., has been over looked so long.. the pracitcal considerations are extent of hardening which is 50% or more, and the time during which it takes effect. these are brought out in the foll0wing brinell harness meadurments made by the preceedure alread published in the american rifleman, on a bullet aloy at three day inetervals after casting... o means the day of casting.. o days+ brinell 13...3 days=brinell 14.5,,,6 days 15.5....9 days brinell 20,, ...12 days brinell 19....15 days brinnell 20.....18 days brinnell 19.5........ thus the alowy reached nearly its full hardness by the ninth day after casting, though it will continue to harden further very slowly for some time longer.. ... this takes pace in softer alloys also. these measurment were made on another bullet alloy at four day intervals after casting... 4 days 9.5,,,,,8 DYS BRINEELLL 10, 12 days brinell 12.5.........16 days BRINELL 13,,,, 20 days brinell 16... . the increase then nearly stopped. the meal thus reached almost full hardness by the 20th day. this may be a more usual time than the nine days of the other alloy. ..............


i will complete the other two paragraphs tomorow i have carpel tunnel and this is getting difficult for me.... dave..

[Ray Newman]

Sometime ago, I believe that I read in the Cast Bullet Association newsletter, that alloys will harden, then start to soften as they age. (http://www.castbulletassoc.org/)

Does anyone else recall this article?

I spent some time trying to find any information about age hardening or softening of lead bullets, buy did not find much that was comprehensible or germane. I did find the following two links of ineterst though.

"A PRIMER ON BULLET CASTING COMPONENTS AND SUPPLIERS"
By Wayne McLerran

“Casting Alloys and Bullet Hardness:

“Depending on the type of alloy and processing, the hardness of a CB [cast bullet] can change in either direction over time. Bullets with high tin-to-antimony content will age-soften significantly over many months, even if tempered. To stop or slow down softening, manufacturers adhere to a “rule-of-thumb” of limiting the tin content to no more than the percentage of antimony. High antimony CBs can be annealed (heated and cooled slowly) to reduce their hardness. But given enough time the bullet will eventually revert back to its original hardness. If you cast your own bullets, freeze storage in your home freezer is one trick used to virtually eliminate age-softening or age-hardening.”

http://www.austinrifleclub.org/Document ... Primer.htm

From “Beartooth Bullets’:

“Since Beartooth Bullets Are Heat-Treated, Do They Age-Soften? :: By on 2001-01-29

“Beartooth Bullets are indeed heat-treated. We heat treat our bullets to a BHN 22, and over the course of 18 months they will age-soften to a BHN 21, where they will remain stabile indefinitely.
We have very carefully and intentionally chosen our alloy with a target BHN of 21 in mind. When heat-treated to BHN 22, the alloy only loses one BHN point when stored at normal room temperatures. This means that the load you work up today with our bullets will perform the same several years from now when stored under normal circumstances. Our bullets will not ever get softer than BHN 21, from aging or storage.”

http://www.beartoothbullets.com/faq/


As an aside, interesting site w/ some cast bullet info:


http://www.lasc.us/CastBulletNotes.htm

[Gunny]

Dave,

That is interesting reading, however, and isn't there always a damn however.

The Universty of Arizona in conjunction with the Dartmuth, sponsered by the Magma Enineering Co of Queen Creek AZ, did a study into the properties of lead alloys. The Magma Eng Co's business is the making of bullets and bullet making machines cast and extruded from lead alloys. Some of there findings where.
For lead to be "Age Hardened" it must be comprised of an "ALLOY" and that alloy must contain at least one of the following compounds. Anitmony, Zinc, Calcium, Bismuth, Arsenic, Cyanide, and this list goes on and on, to about 25 different conponents. With any of these components some very small amount of Age Hardening "Can Occur" this hardening takes place over about two weeks and at that time the lead alloy is fixed. The amount of age hardening is different with different mixtures of these compounds but usually is less than 1/10th of one point on the Brinell Hardness scale.

The use of a Tin and Lead only mixture, produced either "No Change" in hardness at all or a very small amount of "Age Softening" over a very small amount of time.

I am sure that the artical you are referring to is dealing with lead alloy's that do contain some amount of Antimony, as this seems to be the most common material added to lead tin mixtures. If this is the case then i would think that some age hardening MAY occur over a two week period. However as the Magma research found pure lead and tin does not age harden at all.

I personally have some Paul Jones 550 grn creedmore bullets cast from 30-1 lead tin, that I casted over three years ago. They read between 6 and 7 on the brinell hardness scale when they where cast and today three years later the still have the same hardness reading, exactly. If you are in fact using pure 30-1 lead tin and know that it is 30-1 it did not get harder in 10 days. If on the other hand you are using some unknown alloy or alloy of a questionable makeup then all bets are off.

Gunny

[Ray Newman]

See http://www.bpcr.net/index-a.htm

Click on "BPCR.net Forum" on left side of page

“Bullets & Lubes”

“Bullet Hardness” thread by Micheal Rix started on 2/8/’04.

[Ray Newman]

I posted my query ‘bout age hardening/softening on the ASSRA & the MSN BPCR boards.

Here’s a link to the responses:

http://www.assra.com/cgi-bin/yabb/YaBB. ... 1101363121

http://groups.msn.com/BPCR/general.msnw ... 1445192592