Seeing the post about the 22-250 vs the 220 swift got me thinking. And maybe some of you can answer this one I see that the velocities that they are delivering are fairly high and with that being said because they are high does that constitute a tighter twist to stabilize a smaller bullet in flight? Due to the weight of the bullet and the speed at which they travel? Is this a common rule for all or just certain calibers and what ever bullets you are using?
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To those who know the technical aspects of it
- Thread starter TNT
- Start date
I am not sure exactly what you are asking about high velocity and twist.
Twist is the amount of rotation imparted by the rifling to the bullet per inch of travel inside the barrel. Rifling twist help to stabilize the bullet in flight. Longer bullets (often loosely translated as heavier bullets) need a tighter twist to stabilize them, shorter bulelts can have a slower twist and stabilize just fine.
Rotational speed (rpm, if you will, but generally rps) is the velocity in feet per second (fps) times the twist rate in revolutions per foot.
Like this
3,800 feet per second x 1 revolution / 1.16 feet = 3,276 revolutions per second, or approximately 196,500 rpm. Increase the twist rate, and the rpm rises.
Higher velocity has the effect of spinning the bullets faster, but rotational speed is not all there is to bullet stability, there is also the air pressure on the bullet tip, which is why a 222 Remington with a 1:14 twist stabilizes a 55 gr bullet almost as well as a 22-250 with the same twist.
90 years ago, when the 22-250 and the Swift were developed, there were very few heavy-for-caliber 22 caliber bullets because there was little demand for them. People were typically still shooting bigger animals with bigger bullets. There were small caliber/high velocity proponents (Newton, Ackley, Mashburn, etc), but people were still in the bigger bullet frame of mind. It wasn't until the 1950s that the high velocity/small caliber for big game idea gained momentum (Roy Weatherby). The 50 to 55 gr bullets out of a 22-250 or a 220 Swift were considered just fine for varmint shooting. Over the past 15 or so years, people have adopted very heavy-for-caliber bullets for match shooting in order to buck the wind better, and there is some carry-over of that concept to varminting. Heavier bullets need tighter twists to stabilize them, and as those tighter twist barrels have become more available, the use of heavier bullets in formerly "varminting" rifles has increased.
Twist is the amount of rotation imparted by the rifling to the bullet per inch of travel inside the barrel. Rifling twist help to stabilize the bullet in flight. Longer bullets (often loosely translated as heavier bullets) need a tighter twist to stabilize them, shorter bulelts can have a slower twist and stabilize just fine.
Rotational speed (rpm, if you will, but generally rps) is the velocity in feet per second (fps) times the twist rate in revolutions per foot.
Like this
3,800 feet per second x 1 revolution / 1.16 feet = 3,276 revolutions per second, or approximately 196,500 rpm. Increase the twist rate, and the rpm rises.
Higher velocity has the effect of spinning the bullets faster, but rotational speed is not all there is to bullet stability, there is also the air pressure on the bullet tip, which is why a 222 Remington with a 1:14 twist stabilizes a 55 gr bullet almost as well as a 22-250 with the same twist.
90 years ago, when the 22-250 and the Swift were developed, there were very few heavy-for-caliber 22 caliber bullets because there was little demand for them. People were typically still shooting bigger animals with bigger bullets. There were small caliber/high velocity proponents (Newton, Ackley, Mashburn, etc), but people were still in the bigger bullet frame of mind. It wasn't until the 1950s that the high velocity/small caliber for big game idea gained momentum (Roy Weatherby). The 50 to 55 gr bullets out of a 22-250 or a 220 Swift were considered just fine for varmint shooting. Over the past 15 or so years, people have adopted very heavy-for-caliber bullets for match shooting in order to buck the wind better, and there is some carry-over of that concept to varminting. Heavier bullets need tighter twists to stabilize them, and as those tighter twist barrels have become more available, the use of heavier bullets in formerly "varminting" rifles has increased.