Montana Bullet Works
        Better Bullets .... Priced Right ....
   Quality hand-cast bullets for handloaders: competitive and recreational shooters
Use the information on the Twist Rate & Stability Tables below to help pick the right bullet ...
The following tables are based on the Greenhill Formula. Using them will allow you to estimate the heaviest/longest bullet a gun will stabilize based on the caliber (left-most column) and twist rate in inches (top-most row).

 For example, a 45 (.457) caliber rifle with a twist rate of 1 in 18", should be able to stabilize a bullet up to 672 grains or 1.74" in length.

 Maximum Weight of Bullet Stabilized (grains)
 

 Twist>>

7

8

9

10

 11 

   12  

  13 

  14 

  15 

  16 

  17 

  18 

  19 

  20 

  21 

  22 

Caliber

      

       

      

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.429

 

 

 

 939

 854

 783

 723

 671

 626

 587

 553

 522

 494

 470

 447

 427

0.457

 

 

 

 

 

 

 931

 864

 806

 756

 712

 672

 637

 605

 576

 550

 

Maximum Length of Bullet Stabilized (inches)

Twist>>

  7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

Caliber

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.429

 3.94

 3.45

 3.07

 2.76

 2.51

 2.30

 2.12

 1.97

 1.84

 1.73

 1.62

 1.53

 1.45

 1.38

 1.31

 1.25

0.457

4.48

3.92

3.48

3.13

2.85

2.61

2.41

2.24

2.09

1.96

1.84

1.74

1.65

1.57

1.49

1.42

 

            The Greenhill Formula does not, however, take into account bullet shape or muzzle velocity. Both parameters come into play especially when you approach the limit of what a caliber/twist rate combination should stabilize.

            Consider a bullet as a cylinder. A round-nosed bullet is more like a cylinder, has its weight very evenly distributed along its entire length and takes less spin to stabilize. On the other hand, a spitzer-shaped bullet has most of its weight contained within the base half of the bullet. The center of mass is therefore not the middle of the bullet and it will require more spin to keep the nose and base aligned. The moral of the story? When you approach theorized limit of what a caliber/twist rate combination should stabilize, stay away from spitzer-shaped bullets. That is, unless you can keep velocity high.

            Every shooter knows the term velocity. The reloading manuals are full of ballistic tables showing velocity at the muzzle and 100, 200, 300, etc. yards down range. I'll bet, however, that most shooters don't realize that velocity and twist rate determine the speed at which a bullet spins. That spin rate, in revolutions per second or minute, keeps the base and nose of the bullet traveling in the same direction. For example, let's consider the same 45 caliber rifle with a 1 in 18" twist rate. At a muzzle velocity of 1,000 feet per second (fps), the bullet is spinning at 666.67 revolutions per second (rps) or 40,000 revolutions per minute (rpm). At a muzzle velocity of 2,000 fps, that same bullet will be spinning at 1333.3 rps or 80,000 rpm. By contrast, take a 22-250 varmint rifle with a 1 in 12" twist firing a bullet at 3,600 fps. That bullet is spinning at 3,600 rps of 216,000 rpm. The moral of the story? When you approach the theoretical limit of what a caliber/twist rate combination should stabilize and your bullets are keyholing on the target, increase the muzzle velocity (if you can and still stay safe), switch to a more round-nosed bullet shape, or switch to a slightly lighter/shorter bullet.

            Use these tables as a general guideline only. I tell all of my long-range shooting customers, shoot the longest, heaviest bullet that your rifle shoots best. Accuracy is more important in the long-range game than muzzle velocity or bullet shape. And yes, Virginia, you must experiment with many different bullets in order to find the one your rifle likes. And that's why we have the selection we do!


Maximum Weight of Bullet Stabilized (grains)

 Twist>>

7

8

9

10

 11 

   12  

  13 

  14 

  15 

  16 

  17 

  18 

  19 

  20 

  21 

  22 

Caliber

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.224

 100

   87

   78

   70

63

58

54

50

47

44

41

39

37

35

33

32

0.244

140

123

109

98

89

82

76

70

66

61

58

55

52

49

47

45

0.257

173

151

134

121

110

1014

93

86

81

76

71

67

64

60

58

55

0.264

192

168

150

135

122

112

104

96

90

84

79

75

71

67

64

61

0.277

233

204

181

163

148

136

126

117

109

102

96

91

86

82

78

74

0.284

258

226

200

180

164

150

139

129

120

113

106

100

95

90

86

82

0.308

357

312

277

250

227

208

192

178

166

156

147

139

131

125

119

113

0.311

371

324

288

259

236

216

200

185

173

162

153

144

137

130

124

118

0.323

431

377

335

302

274

252

232

216

201

189

178

168

159

151

144

137

0.338

517

452

402

362

329

302

278

259

241

226

213

201

191

181

172

165

0.348

581

508

452

407

370

339

313

291

271

254

239

226

214

203

194

185

0.357

644

563

501

451

410

375

347

322

300

282

265

250

237

225

215

205

0.375

784

686

609

548

499

457

422

392

366

343

323

305

289

274

261

249

0.410

 

980

871

784

712

653

603

560

522

490

461

435

412

392

373

356

0.429

 

 

 

939

854

783

723

671

626

587

553

522

494

470

447

427

0.457

 

 

 

 

 

 

931

864

806

756

712

672

637

605

576

550

 

Maximum Length of Bullet Stabilized (inches)

 Twist>>

  7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

Caliber

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.224

 1.08

 0.94

 0.84

 0.75

 0.68

 0.63

 0.58

 0.54

 0.50

 0.47

 0.44

 0.42

 0.40

 0.38

 0.36

 0.34

0.244

1.28

1.12

0.99

0.89

0.81

0.74

0.69

0.64

0.60

0.56

0.53

0.50

0.47

0.45

0.43

0.41

0.257

1.42

1.24

1.10

0.99

0.90

0.83

0.76

0.71

0.66

0.62

0.58

0.55

0.52

0.50

0.47

0.45

0.264

1.49

1.31

1.16

1.05

0.95

0.87

0.80

0.75

0.70

0.65

0.61

0.58

0.55

0.52

0.50

0.48

0.277

1.64

1.44

1.28

1.15

1.05

0.96

0.89

0.82

0.77

0.72

0.68

0.64

0.61

0.58

0.55

0.52

0.284

1.73

1.51

1.34

1.21

1.10

1.01

0.93

0.86

0.81

0.76

0.71

0.67

0.64

0.60

0.58

0.55

0.308

2.03

1.78

1.58

1.42

1.29

1.19

1.09

1.02

0.95

0.89

0.84

0.79

0.75

0.71

0.68

0.65

0.311

2.07

1.81

1.61

1.45

1.32

1.21

1.12

1.04

0.97

0.91

0.85

0.81

0.76

0.73

0.69

0.66

0.323

2.24

1.96

1.74

1.56

1.42

1.30

1.20

1.12

1.04

0.98

0.92

0.87

0.82

0.78

0.75

0.71

0.338

2.45

2.14

1.90

1.71

1.56

1.43

1.32

1.22

1.14

1.07

1.01

0.95

0.90

0.86

0.82

0.78

0.348

2.60

2.27

2.02

1.82

1.65

1.51

1.40

1.30

1.21

1.14

1.07

1.01

0.96

0.91

0.87

0.83

0.357

2.73

2.39

2.12

1.91

1.74

1.59

1.47

1.37

1.27

1.19

1.12

1.06

1.01

0.96

0.91

0.87

0.375

3.01

2.64

2.34

2.11

1.92

1.76

1.62

1.51

1.41

1.32

1.24

1.17

1.11

1.05

1.00

0.96

0.410

3.60

3.15

2.80

2.52

2.29

2.10

1.94

1.80

1.68

1.58

1.48

1.40

1.33

1.26

1.20

1.15

0.429

3.94

3.45

3.07

2.76

2.51

2.30

2.12

1.97

1.84

1.73

1.62

1.53

1.45

1.38

1.31

1.25

0.457

4.48

3.92

3.48

3.13

2.85

2.61

2.41

2.24

2.09

1.96

1.84

1.74

1.65

1.57

1.49

1.42

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