My Lee .459-405 bullets weigh 377 grains!

[namsag]

Casting Lee .459-405HB, out of Roto 20-1, ladle poured, at 800* in RCBS Pro-Melt 2. It took me a little practice to get going, but started turning out some really nice-looking bullets. I was pleased with their appearance and stopped at 50 for the session.

Checked the diameter at consistent .462, and Low and Behold, when I weighed them they were remarkably consistent, about 40 of them are within +/- 0.2 grains...from 377.8!

I didn’t really expect them to be 405 grains on the dot , but What in the Sam Hill?

[Dusty Bannister]

Generally BP type bullets are cast of pure lead. The tin-lead bullets are going to be lighter. The rest could be temperature related, or just how the mold was made.

[wmitty]

Is the Roto 20-1 supposed to be 20 parts lead to one part tin? Anyone know the density of 20/1?

[GregLaROCHE]

Who was the mold made by?

[mehavey]

Given the relative densities of lead (11.35) and (white) tin (7.27),
I'd expect a 405 gr pure lead bullet to weigh 398 at a 20-1 ratio.

From experience, I can pretty much guarantee the RotoMetal is spot on.

[Larry Gibson]

I would suspect the scale.....balance beam or electronic?

[Targa]

You said 40 of them were within +/- .02 of 377.8…..what were the other ones at?

[Dusty Bannister]

From the LASC site, just to give a reference.


Expected (Approximate) alloy weight variation from bullets cast of linotype

Bullet Weight Bullet Weight Bullet Weight Bullet Weight
Linotype - No GC 1 - 10 Alloy - No GC Wheel Weight - No GC Pure Lead - No GC
53.0 gr. + 2.3 gr. + 2.6 gr. + 4.7 gr.
93.0 gr. + 4.0 gr. + 4.6 gr. + 8.3 gr.
118 gr. + 5.0 gr. + 5.8 gr. + 10.5 gr.
147.0 gr. + 6.3 gr. + 7.2 gr. + 13.1 gr.
165.0 gr. + 7.0 gr. + 8.1 gr. + 14.7 gr.
177.0 gr. + 7.5 gr. + 8.7 gr. + 15.8 gr.
237.0 gr. + 10.1 gr. + 11.7 gr. + 21.2 gr.
401.0 gr. + 17.1 gr. + 19.8 gr. + 35.8 gr.

Not sure if this will stay in this format.

[Tom Myers]

Casting Lee .459-405HB, out of Roto 20-1, ladle poured, at 800* in RCBS Pro-Melt 2. It took me a little practice to get going, but started turning out some really nice-looking bullets. I was pleased with their appearance and stopped at 50 for the session.

Checked the diameter at consistent .462, and Low and Behold, when I weighed them they were remarkably consistent, about 40 of them are within +/- 0.2 grains...from 377.8!

I didn’t really expect them to be 405 grains on the dot , but What in the Sam Hill?

Pure Lead has a Specific Gravity of 11.345
Pure Tin has a Specific Gravity of 7.337
Pure Antimony has a Specific Gravity of 6.7

Calculate the Specific Gravity of 1 part Tin and 20 Parts Lead:

20/21 = 0.9524 = Ratio of Lead in the alloy.
1/21 = 0.04761 = Ratio of Tiin in the alloy.


(0.0476 / 7.337 )+ (0.9524 / 11.345) = 0.090437
1 / 0.090437 = 11.057
The specific gravity of the 20-1 alloy is 11.057

11.057 / 11.345 = 0.97465 * 100 = 97.5% of pure lead
405 grains * 0.975 = 394.875 grains
So I f the mold casts a pure lead bullet weighing 405 grains you could expect a bullet cast of Roto 20-1 to weigh 394.7 grains.


Roto Hardball alloy is 92% Lead, 2% Tin and 6% Antimony.
(0.92 / 11.345) + (0.02 / 7.337) + (0.06 / 6.7)= 0.09277
1/ 0.09277 = 10.779
10.779 / 11.345 = 0.95010 * 100 = 95.01% of pure lead.
11.345 * .9501 = 10.7789
Roto Hardball has a specific gravity of 10.7789 and would cast a bullet weighing 384.8 grains.

Roto Superhard alloy is 70% Lead and 30% Antimony
(0.7 / 11.345) + (0.3 / 6.7) = 0.106477
1 / 0.106477 = 9.3917.
9.3917 / 11.345 = 0.8278 * 100 = 82.78% of pure lead.
Roto Superhard has a SG of 9.3917 and would cast a bullet weighing 335 grains.

****************

What it all boils down to is that all this is just numbers and speculation untill you have and absolute known quantity to start from.

Find some pure lead and cast a bullet. Weigh it. Then you willl have a known quantity and can then determine what your alloy consists of.

[mehavey]

This is high-school weighted avrage stuff"


Density of the mix is:
=(20*Pb + 1*Sn)21
=(20*11.35 + 1*7.34)/21
=11.16= 98.3% that of pure lead

405gr Lead bullet would weigh 405 * 98.3% = 398.2gr as mixed

[Tom Myers]

This is high-school weighted avrage stuff"


Density of the mix is:
=(20*Pb + 1*Sn)21
=(20*11.35 + 1*7.34)/21
=11.16= 98.3% that of pure lead

405gr Lead bullet would weigh 405 * 98.3% = 398.2gr as mixed

I know that method seems logical, but I went down that rabbit hole when I first began designing bullets. All my calculations were close but were never exactly right.
I finally stumbled on an old gold assayers manual that laid out the method that produces exact results.

20 lbs of pure lead = 799.634 cc or 48.7967 cubic inches.
1 lb of pure tin = 61.8225 cc or 3.7726 cubic inches.
21 lbs should then = 861.4565 cc or 52.5693 cubic inches.
a 20 lead + 1 tin alloy has a specific gravity of 11.057365 Grams per cubic centimeter.
21 lbs of 1:20 alloy = 147,000 grains = 9,525.438 Grams / 11.057365 = 861.4565 cc or 52.5693 cubic inches.

If the alloy's Specific Gravity is 11.16, then volume of the alloy would be: 9525.438 Grams / 11.16 = 853.5339 cc or 52.08 cubic inches.
I realize that the differences in the values are not much but, until I finally hit on the correct procedure, those small differences used to drive me crazy when trying to accurately predict bullet weights from known alloys.

One needs to add the RECIPROCALS of the percent-density values of the metals and then divide 1 by that sum.
instead of adding (20*11.35) and (1*7.34) / 21 =11.16.
The Ratio of Lead in the alloy is 20/21 = 0.95238.
The Ratio of Tin in the alloy is 1/21 = 0.047619.
The Specific Gravity of Lead is 11.345.
The Specific Gravity of Tin is 7.337.
Divide 1 by the sum of the reciprocals of the Ratios/Sectional Density ~ 1 / [ (0.95238 / 11.345)+ (0.047619 / 7.337)]= 11.057365

[mehavey]

When adding by weight (duhhhhh), you are correct Tom.
(Dumb, grasshoppa.....)

[namsag]

These were weighed on my electronic scale but then quickly verified on the balance because I didn't quite believe it. Most od the rest are within a grain, except for two that are 3 or 4 grains light. On further inspection they had defects in the bases.

[Whole Bunches]

As a data point, my Lee 459-405 with my 20/1 cast come out at .462” and 395 gr.

[Harter66]

I have a PB/HB MP 462-420 . It was a special run I guess as it cast 50/50 .460-417 PB and .460-380 HB .

I mention that because there are so many designs designated as Hollow or not and cast accordingly . Lee also makes a bullet that is basically a 1 band shorter 405 , much like the 405/450 relationship , that would weigh about 380 .

[tmanbuckhunter]

Mine drops bullets in the 389-390 range, but it's Lee we're talking about here. Being way off wouldn't surprise me. The most important thing in this realm is bullet length, not so much weight... weight is a byproduct of the length. Having the hollow base to reduce the weight but keep the length is why it's there, so if it shoots well, who cares?

[Tom Trevor]

This reminds me of when Spencer Wolf had Lee make the first run of the 405 Hb molds. The first year all was well then he would get small lube grooves and 427 weight another run was 385 and very large grooves. Our club bought a group of twent and when Lee was called about the differences a fine individual retorted that they are CNC cut and are ALL the same and go have your eyes checked!

[wmitty]

Tom Myers
Thanks for taking the time to walk us thru this! It would seem the volume of the machined cavity would be critical in trying to use the calculated alloy density to account for the lighter boolits the o. p. is getting, possibly slightly undersized in some way.