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Is it necessary or desirable to crimp cast bullets in rifle cartridges?

 

The experts do not seem to agree on this one.

 

Some say, never crimp. Seat the bullet out as far as possible so it is engraved by the rifling and the rifling will provide enough resistance to insure consistent ignition of the powder charge with no damage to the bullet by the crimp or by the jump to the riflling.

Others say It is always necessary to crimp rifle ( as well as handgun ) cast bullets.

The first test of this theory was spread over several months in 2011.

 

The results were dramatic and conclusive.

 

The crimped loads produced 100 yard five shot groups smaller than the three shot groups produced by the loads with the bullet seated into the lands.

Summary

Bullets seated into the lands.

14 three shot groups average 2.12 inches

Velocity Variation
Average of eight six shot strings
Average Standard Deviation = 109 fps

 

Bullets crimped into the second lube ring leaving one lube ring exposed:

10 three shot groups average 0.91 inches

7 Five shot groups average 1.89 inches.

Velocity Variation
Average of eight six shot strings
Average Standard Deviation = 45 fps

 

Conclusion:

Crimping may not be necessary but it certainly improves the results.

 

DATA:

.38-55 Winchester

Cast Bullet Crimping Test

Winchester 1885 Replica

Nikon 24x Variable

Test Load

Powder

2015

Grains

22

Bullet

216 gr modified 375248

Sized

Lyman 4500 .377

Lube

Lyman 50/50 Alox Beeswax

Cases

Star-Line.

Velocity

1350

     

Distance

100 Yd

Sights

Nikon 14x

Crimp

None*

Crimped

Crimped

No Shots

3

3

5

Group

1

2.68

0.71

1.51

2

1.36

0.76

2.44

3

4.76

2.12

2.56

4

0.83

0.69

1.82

5

4.80

0.92

2.36

6

2.97

0.81

1.28

7

1.03

0.68

1.27

8

0.51

1.46

9

2.00

0.45

10

1.41

0.48

11

3.50

12

1.31

13

0.71

14

1.87

15

Average

2.12

0.91

1.89

Avg Deviation

1.16

0.36

0.48

Std Deviation

1.42

0.51

0.56

*Un-crimped bullets seated into the rifling 1/8 inch

 

Chronograph Consistency
Dates Various
Tempratures Various
Shot strings Six shots
Standard Deviation of six shot strings
Shot string No Crimp Crimped
1 58.6 31
2 72 34
3 122 61
4 93 38
5 91 44
6 79 48
7 144 37
8 219 65
Avg SD 109 45

 


NOTE:  Check back occasionally. This data will be expanded as experiments continue.

 

 
 

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