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Cast Bullet Weight Variations

How uniform should the weights of cast bullets be?




Cast bullets vary in weight. Even bullets cast in successive pours and in the same mold cavity will not weigh the same. But we want all our bullets to weigh the same. Just how much weight variation is normal,  acceptable?


These weight test ware done over a long period of time. Some of them were deliberate and some were recorded as part of some other test.

These cast bullet weight tests all have these things in common.

Bullet weight variations  are conducted with a single pot of metal to keep the let, tin, antimony, proportions and therefore the density of each bullet as constant as possible. All bullets were cast by myself.

Unless otherwise specified the bullets weighed came from all the cavities of the mold. The purpose of the test is to determine how much variation is normal in an actual casting session. Obvious flaws were not kept. They were returned to the pot and do not affect the test results. The bullets weighed included only "Keepers".

 

Test 20110829

Mold:

Six cavity Lee mold 430-240-SWC

Pot:

Lee 4-20 production pot

Casting:

Bottom pour - 3/4 inch drop

Alloy:

Lyman No.2 Clone

Nominal Weight

240gr

Weight Groups

239 means 239.0 to 239.9 grains. Etc.

Number of bullets of each grain weight

Weight Gr.

No.

237

6

238

12

239

68

240

86

241

94

242

14

243

1

Total

281

Range = 243.9 - 237.0  = 6.9
Average = 240.0534
Variation = 2.87%

Keeping only the three largest groups:

Range = 241.9-239  = 2.9 grains
Average = 240.1048
Variation = 1.2%

Note that since we cannot weigh more accurately than one tenth of one grain, calculating the average to more than one decimal point is meaningless. IN the both example to the accuracy limits of our testing procedures, both groups of bullets had exactly the same average weight - 240.1

Also note that Lee specifies that mold to produce bullets weighing 240 grains using Lyman #2 alloy. Our average of 281 bullets was 240.1.

 

Cast Bullet Weight Consistency

Mold Lee 379-247 RF

Same Mold Cavity

Same Pot of metal

Same Casting session.

Alloy = 50% WW - 50% Linotype

Nominal weight 247gr.

Bullet

Bottom

Ladel

No.

Pour

Pour

1

236.30

237.80

2

236.90

237.80

3

235.80

237.60

4

236.70

237.60

5

235.40

237.30

6

236.30

237.30

7

237.30

236.90

8

236.30

237.70

9

237.20

237.50

10

237.10

237.00

11

237.40

237.80

12

237.50

237.20

13

236.00

237.30

14

235.80

237.10

15

237.40

237.70

16

237.90

237.40

17

236.00

237.60

18

237.50

237.70

19

237.40

238.00

20

237.10

237.30

21

236.70

237.40

22

237.50

237.90

23

237.40

237.50

24

237.50

237.10

25

236.50

237.40

26

237.60

238.30

27

237.70

237.30

Total

6396.20

6412.50

Average

236.90

237.50

Max

237.90

238.30

Min

235.40

236.90

Variation

2.50

1.40

Std Deviation

0.69

0.32

 

 

 

 

 
 

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