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Test the assertion:

Plain Base Cast Bullets are Inherently More Accurate than Bevel Based Cast bullets




This test began on 02/20/12 with the casting of the first bevel base bullets.
It will take several months to complete.

This page will be updated as new steps are completed.

 

First results posted 02/29/2012

Concluded 03/26/2012

Revised 08/11/2012 - add .357 Mag groups


Assertion:

Bevel base bullets are inherently less accurate than flat base bullets.

Proposal: Test the assertion.

Variables:

Control these variables:

Bullet design. Vary only the base.
Bullet. Cast all bullets from the same pot of alloy.
Alloy. 100% clip on wheel weights.
Sizing. Size all bullets with same sizing die at the same time.
Lube. Use same lube on all bullets lube them all at the same time.
Cases. Use commercial cases known to be from the same manufacturing lot.
Powder. Weigh all charges.
Primer. Use primers from same brick of 1000 for all tests.


Method:

Don't care about 'state of the art' equipment possibilities.

Use equipment that is available and frequently used by "Joe Caster."

Testing a bullet xxx in plain base against bullet yyy in bevel base will prove nothing.

I am unable to acquire the same bullet in both base styles.
( Unwilling to spent the money. ) So I will need to make my own.

Start with well used Lee two cavity mold 358-158-SWC.
This bullet from this exact mold has been tested extensively by myself and found to be
very accurate.

Test platform will be Thompson Contender .357 Mag with Weaver 8x hand gun scope.

Test groups will be fired at 50 Yards.



Steps:

Step 1)
Cast 500 bullets using only the front cavity.

step 2)
Remove the bevel from the front cavity.

Step 3)
Cast 500 plain base bullets from the modified cavity.

Step 4)
Select the most accurate recorded load for this bullet from my loading data.

Step 5)
Select 100 matched .38 special cases and 100 matched .357 cases.
Matched means cases that were bought as factory ammo and kept together after firing.

Step 6)
Trim all cases to uniform length.

Step 6)
Load 50 .38 specials with bevel base bullets in matched cases.
Test fire 10 5 shot groups.

Step 7)
Load 50 .38 specials with plain base in the same 50 matched cases.
Test fire 10 5 shot groups

Analyze data

Wait a week and repeat.
Analyze data.

This will be 20 5 shot groups with each bullet style. Each 5 shot group will be fired with
loads loaded in the exact same cases


Repeat the same test with the most accurate .357 Mag load in the .357 Mag cases

 

Results Summary:

80 5 shot groups:
  Flat Bevel

Base Base
No Groups
40 40



Average 1.37 1.38
Std Dev 0.29 0.29



 



Raw Data:

 

02-25-12

Test Load
Load .38-0059
4.2 gr A. No. 2
CCI 100 SP
.358-158-SWCSized with Lee Die .357
Actual diameter .357 - .3575
Alloy unknown. Very hard bullets.
I thought the lead in the pot was BNH 12.
Turns out it was MUCH harder.
The bullets measured BNH 17 to BNH 22

Control Load:
Load .38-0054
Exactly the same as the test load with a beveled base bullet.
The control load bullet was 100% Clip on wheel weights.


Flat Base Bevel Base
Load 38-0059 38-0059

BNH 20-22 BNH 20-22
Control Group 0.98  
Test Group

1 0.98 1.50
2 1.18 1.41
3 1.38 1.30
4 2.28 1.76
5 1.82 1.51
6 1.66 1.29
7 1.51 1.18
8 1.46 1.40
9 1.72 1.36
10 1.13 0.88
Avg 1.51 1.36
SD 0.38 0.23
Control Group   1.19

Groups are numbered in the order they were fired. The flat base groups were fired first, then the bevel base.

The control groups were fired first and last. The control group tests the shooter and the firearm with a load of proven accuracy. Control group 1 was fired before the first of the test groups and the control group 2 was fired after the last of the 20 five shot groups.

Control group 1 measured 0.88. Control Group 2 measured 1.19

I was very disappointed in the accuracy from the very beginning. This was the exact same load as the control group except with a flat base. After checking the obvious, Bags, hold, wobble, glasses, scope mount and lenses, I looked down the bore. After only  four groups there was significant leading in the first inch.

Something was wrong. This load simply does not lead. I have fired thousands of rounds of this load. in three different .357s with  no leading.

After completing the first ten groups, I pulled out my bore cleaning loads. I usually fire three to five rounds of .357 Mag loads with gas check bullets to remove leading. I have found this to be a very effective way to "start clean" when testing loads that produce unexpected leading. To my considerable surprise, five rounds had no effect at all.

When I got back to the shop, I tested some of the bullets and to my amazement they were very hard. I thought I cast them from an alloy of about 12 BNH but three bullets actually tested 17, 21, 22.

Test 2)

Exactly the same load as above except bullets were Cast from a known alloy with BNH 10



Flat Base Bevel Base
Load 38-0059 38-0059
  BNH 10 BNH 10
Control Group 0.92  
Test Group

     
     
1 1.04 1.77
2 2.05 2.00
3 0.96 1.11
4 2.04 1.86
5 1.66 1.23
6 1.51 1.50
7 1.09 1.89
8 1.92 1.21
9 1.66 1.51
10 1.11 2.05
1.50 1.61

0.43 0.35
 
 
ControlGroup
1.69

Well, the softer bullets solved the leading problem but I am still disappointed with the accuracy. The bevel base load should be averaging below 1.25 based on prior shooting.

03/05/2012

Reverted to Bullseye

Test Load .38-0060
3.0 gr Bullseye
CCI 100 SP
.358-158-SWCSized with Lee Die .357
Actual diameter .357 - .3575
Alloy Soft.
Exact same pot as the batch from the previous test
BNH 10-11

The first two control groups were fired with Factory Wadcutters

The last two Control groups were fired with Winchester Super-X 130 gr FMJ.


Test 3

Flat Base Bevel Base
03/05/12 BNH 10 BNH 10



CG 1.11
CG 1.12
1 1.28 1.46
2 1.57 1.18
3 1.28 1.28
4 0.97 0.82
5 1.00 1.19
6 1.04 1.37
7 1.24 1.06
8 0.86 1.05
9

10


Average
1.16 1.18

Standard Deviation
0.23 0.20






CG 1.14 0.92
CG 1.1 1.69

 

Test Load .38-0060
3.0 gr Bullseye
CCI 100 SP
.358-158-SWCSized with Lee Die .357
Actual diameter .357 - .3575
Alloy Soft.
Exact same pot as the batch from the previous test
BNH 10-11

Date 03/26/2012

Test 4

Flat Base Bevel Base
03/26/12 BNH 10 BNH 10



CG 1.11
CG 1.12
10 1.16 1.26
1 1.81 1.04
2 1.36 1.36
3 1.49 1.10
4 1.50 1.42
5 0.94 1.35
6 1.09 1.54
7 0.96 1.42
8 1.12 1.31
9 1.38 1.29
10 0.82 1.06
SD 0.31 0.17




.357 Mag Data:

.357 Mag 0040 11.6 gr A No 9.
ZERO leading

Flat Base Bevel Base
03/05/12 BNH 10 BNH 10
1 1.21 0.89
2 0.86 1.48
3* 3.62 0.69
4* 3.05 2.12
5* 2.74 1.87
6

7

8

9

10

Average 2.30 1.41
Std Dev. 1.20 0.61

* These groups were quite a surprise.
They were fired with loads from the same batch as groups 1&2
Subsequent inspection and groups proved there was no problem with the gun.

 

 



Raw Data:

 
Load Group Flat Bevel


Base Base




4.2 gr A. No. 2 1 0.98 1.50

2 1.18 1.41

3 1.38 1.30

4 2.28 1.76

5 1.82 1.51

6 1.66 1.29

7 1.51 1.18

8 1.46 1.40

9 1.72 1.36
3.0 gr Bullseye 10 1.13 0.88

1 1.04 1.77

2 2.05 2.00

3 0.96 1.11

4 2.04 1.86

5 1.66 1.23

6 1.51 1.50

7 1.09 1.89

8 1.92 1.21

9 1.66 1.51
3.0 gr Bullseye 10 1.11 2.05

1 1.28 1.46

2 1.57 1.18

3 1.28 1.28

4 0.97 0.82

5 1.00 1.19

6 1.04 1.37

7 1.24 1.06

8 0.86 1.05

9 1.82 1.82
3.0 gr Bullseye 10 1.16 1.26

1 1.81 1.04

2 1.36 1.36

3 1.49 1.10

4 1.50 1.42

5 0.94 1.35

6 1.09 1.54

7 0.96 1.42

8 1.12 1.31

9 1.38 1.29

10 0.82 1.06





Average 1.37 1.38

Std Dev 0.29 0.29











 

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