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TESTING PURE LEAD, LINOTYPE,
THERMOMETERS & HARDNESS

These simple metallurgical principle presented herein
has been known for well over 100 years

REQUIREMENTS: A laboratory grade accurate thermometer is recommended. My thermometers are of such quality. Best to have graph paper, melting pot, sweep second hand timer. The physical principle is a pure metal or eutectic alloy will melt or solidify at constant temperature. In bullet alloy systems there may be only one unique composition which is a eutectic. Using lead as a base it is lead/tin or lead/tin/antimony. For testing melt start temperature needs to be about 50 to 70 degrees F above the solidification temperature. Even cheapie thermometers, if reasonably repeatable are useful, just not necessarily accurate for purity & composition work.

PURE LEAD Use 99.85% purity if available. Lead melts and solidifies at a constant temperature of 621 F. Use 700F, The thermometer is placed so it can be read without parallax. Turn off heat, read and plot decreasing temperature on the vertical axis and time on the horizontal axis. Time interval for reading the thermo is directly related to pot capacity and material. Smaller the pot shorter interval, gas fired large cast iron pot much longer interval. Pure liquid lead will stop cooling at 621F. This is an invariant temperature and if the thermo indicates a different constant reading record and it has just been calibrated. Result is a horizontal line usually called a 'flat' or 'step'. When lead is completely solid the decreasing temperature measured is simply the rate of cooling of the solid lead and the pot. A heating curve is required to extract the thermometer or if timed right it may be removed as soon as a drop is noted. This test recognizes less than 1% impurities, usually much less.The unit error has been determined. Record this error. My daily use thermometers measure within +/- 5 degrees.

EUTECTIC 4/12/84 LINOTYPE, An alloy with 4% tin, 12% antimony, 84% lead. The alloy will give a flat cooling curve line. Very slight variations w/ some thermometers may appear to give a flat. Turn off heat, make same measurements as for lead. Eutectic linotype flat is at 465F. PURE TIN. Same test as lead. Temperature will be 449F. TIN/LEAD eutectic is 63% tin/37% lead, same test, temperature 362F. Kester markets this alloy as Ultra Pure Solder. 60/40 solder may appear the same as the ‘curve’ is very flat in this composition region.

ALL OTHER alloys, WW (wheel weight), type metals other than linotype, 2/6/92, Lyman #2 5/5/90, 8/8/84, any combination of the foregoing or scrap anything will not give the 'flat' plot. All usable lead alloys for bullet casting melt below 621F and are solid at 464F as the eutectic phase composition is the last to solidify. Note word phase as any lead/tin/antimony alloy with 1 to 1.5% tin and 2 to 3% antimony may have eutectic present.

ANTIMONY/LEAD eutectic is 11.2% antimony and 88.8% lead and 484F. This alloy is not common. 1% or more tin will modify this temperature significantly. I have never made or measured this alloy.

OTHER SOLDERS, 30/70, 40/60, 50/50 and 60/40 (above) solders will not give a true flat. Lead free solders do not give a flat nor will the decorative alloy pewter.

HARDNESS TESTING. Linotype, Lyman # 2 and pure lead are the usual standards that permit comparison of unknown alloys in order to gain some information. Lead is Brinell Hardness Number (Bhn) 5, Lyman #2 of composition 5/5/90 is 15 and eutectic linotype 22. ‘Hardcast’ handgun alloy 2/6/92 is Bhn 15 to 16. Lyman alloy 8/8/84 is also 22 due to the equal tin-equal antimony phase in the alloy. With these as standards simply squeezing an unknown ingot and a standard in a vise will indicate what the approximate hardness is.

This is not absolutely necessary. Squeezing any two ingots of different composition will give relative hardness. The smaller indent is the harder alloy or metal. Usually a good quality caliper and a 10X magnifier will give excellent results. If standards are available, first use Lyman #2 5/5/90 as the unknown will be harder or softer OR possibly the same. The common commercial alloy 2/6/92 will just about equal Lyman #2 unless made from wheelweight scrap which age hardens. The design of the hardness tester has a significant bearing on the accuracy, ease of use and reproducibility of the results. No sharp point penetrator hardness tester will measure Brinell. They should be "calibrated" usually using the 3 standard alloys above (or something near thereto). Some are close and some have significant errors BUT this is not important as long as the same equipment is used for comparison of your bullets and/or alloys. The physical and mechanical principles are quite simple. A spherical surface such as the ball used in the Brinell test or micro ball in Meyer makes an entirely different displacement of the metal than a pointed penetrator. The amount and method of displacement is a measure the force required to move the metal. Brinell uses a fairly complicated formula which requires some mathematics. The only 'pointed' penetrator system I think I understand is Knoop, which is a precision ground diamond laboratory unit using a microscope to measure the indent width and length, not depth. It makes no difference which method is used, just be consistent and results will be adequate for bullet casting.

BPCR lead/tin alloys are hardest the day cast. 20/1 is about 12.5 Bhn and decreases to ~10 Bhn in a week or so. The lower the tin content the softer the alloy however the less the hardness decreases. More tin lighter but larger bullet diameter. Some BPCR shooters adjust alloy to each rifle's throating and groove diameter. Ingots will be quite close to bullet hardness with time, unlike other alloy bullets, especially WW which age hardens.

 

 

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