Reply To: Barrel Twist vs Powder Burn

Forums Reese Bottom Chat Room Barrel Twist vs Powder Burn Reply To: Barrel Twist vs Powder Burn

#1440
Ron Lewis
Participant

Well Surrell, if you greatly simply all the variables and if you chronographed your loads, the one with the highest velocity stays in the barrel the shortest time. With that being said here is some more food for thought

1. Years ago when I was working on a project with Tioga Engineering manufacturing the next great 50 cal BMG VLD bullets we were trying to get some unbelievable speeds out of the round. The highest velocities were obtained by shooting the projectile down a barrel that was oversized and a smooth bore. We were trying to penetrate Armor plate 4 inch thick. It can be done.

The twist of the barrel determines the RPM of the bullet. Generally speaking the more twist the more drag getting the bullet started. The difference in drag would be very small and you will have a hard time measuring any difference with such a small difference in twist. The higher twist barrel will have a sharper pressure curve.

2. Note: Higher twist means a lower number or faster spin on the bullet. 1 in 10 twist means the bullet makes one revolution in 10 inches vice a 1 in 12 which makes a revolution in 12 inches

3. Faster twist of course means that a barrel can stabilize a bullet which is longer and heavier. This stabilization occurs from the bullet rotating about it’s central axis. (Just like a gyro)

4. Although the velocity difference between the two barrel twist is very small the spin on the bullet is greatly effected. Lets just say for example that you are shooting your 308 Win with a 155 gr Palma bullet at 2650 fps out of your two barrels. At 2650 fps your bullet travels 31800 inches in one sec. Here’s the RPM of the bullet, if my math is correct

1 in 10 twist = 190800 RPM ( 20% faster than the 12 twist)
1 in 12 twist+ 159000 RPM