now a 300-win mag with a 1-12 twist barrel pre 1980s

To determine the optimal bullet weight for a .300 Winchester Magnum with a 1:12 twist rate and a 24-inch barrel, we need to consider the stability factor while keeping in mind the medium barrel length, which should provide good velocities. Here’s a detailed process to identify the suitable bullet:

Bullet Selection Criteria

1. Twist Rate: A 1:12 twist rate is slower and typically stabilizes lighter bullets better than heavier, longer bullets.
2. Caliber: .300 Winchester Magnum (.308 caliber).
3. Barrel Length: A 24-inch barrel is of moderate length, providing good velocity.
4. Bullet Type: Considering both monolithic and lead core bullets.

Optimal Bullet Weights

For a 1:12 twist rate, you generally want to use lighter bullets as the slower twist rate will stabilize these better. Common weights for .300 Win Mag include:

• 150 grains
• 165 grains
• 168 grains

Example Calculation for a 165-Grain Bullet

Using the Miller Stability Formula

Let’s assume a 165-grain lead core bullet with an approximate length of 1.3 inches and a muzzle velocity of 3050 fps.

1. Parameters:
   • Caliber (D): 0.308 inches
   • Twist Rate (t): 12 inches (1 turn in 12 inches)
   • Velocity (v): 3050 fps
   • Bullet Length (L): 1.3 inches
   • Bullet Mass (m): 165 grains
2. Calculating Stability Factor (S):

S=30×(165)2×3050(12)2×1.3×(1+(1.3)2(0.308)2)S = \frac{30 \times (165)^2 \times 3050}{(12)^2 \times 1.3 \times (1 + \frac{(1.3)^2}{(0.308)^2})}S=(12)2×1.3×(1+(0.308)2(1.3)2​)30×(165)2×3050​

Let’s calculate this step-by-step.

Step-by-Step Calculation

L=1.30.308=4.22L = \frac{1.3}{0.308} = 4.22L=0.3081.3​=4.22

S=30×1652×3050144×1.3×(1+4.222)S = \frac{30 \times 165^2 \times 3050}{144 \times 1.3 \times (1 + 4.22^2)}S=144×1.3×(1+4.222)30×1652×3050​

S=30×27225×3050144×1.3×(1+17.8)S = \frac{30 \times 27225 \times 3050}{144 \times 1.3 \times (1 + 17.8)}S=144×1.3×(1+17.8)30×27225×3050​

S=2488500000187.2×18.8S = \frac{2488500000}{187.2 \times 18.8}S=187.2×18.82488500000​

S=24885000003513.6S = \frac{2488500000}{3513.6}S=3513.62488500000​

$S=708.28$

Finally:

S=24885000003513.6=2.0S = \frac{2488500000}{3513.6} = 2.0S=3513.62488500000​=2.0

With a stability factor (S) of approximately 2.0, this bullet is at the higher end of the stable range (1.3 to 2.0), indicating it will be stable.

Recommended Bullets

Based on the criteria and calculations, the following bullets should be well-suited for a .300 Win Mag with a 1:12 twist rate and a 24-inch barrel:

Lead Core Bullets

• Hornady InterLock 165 grain: Good for hunting with controlled expansion and deep penetration.
• Sierra GameKing 165 grain: Reliable performance for hunting with a good balance of accuracy and terminal performance.

Monolithic Bullets

• Barnes TTSX 165 grain: Solid copper with excellent penetration and weight retention, suitable for a variety of game.
• Nosler E-Tip 150 grain: Lead-free with high ballistic coefficients, providing good accuracy and terminal performance.

Conclusion

For a .300 Winchester Magnum with a 1:12 twist rate and a 24-inch barrel, bullets in the 150-165 grain range are typically well-suited. Both lead core and monolithic bullets can be effective, depending on your specific needs, such as hunting regulations (lead-free requirements) or specific performance preferences (accuracy versus terminal performance).

Always test different bullets at the range to ensure they perform well with your specific firearm setup. At 360arms, we can help you select the right ammunition for your needs, ensuring the best performance and accuracy for your shooting activities.