Was watching a podcast by Barnes bullets with a guy from vortex ( Ryan Muckenhirn) discussing bullets and rotational velocity was touched upon, which I take it as the faster a bullet is spun the more likely it is to expand or blow up in some cases, I know bullet construction has a lot to play in it and like most things it's never straightforward, I found it very interesting and just from my own limited experience the other night I shot a fox with my new tikka 223 1 in 8 twist, with a remington 55 grain soft point and it expanded way more than I ever experienced before, basically almost blowing up on a chest shot and this is out of a 16 inch barrel, so probably 200 fps slower than factory velocity, my .222 with 50 grain soft points through a 1 in 14 barrel would usually get a pass through on a chest shot, interesting on others thoughts on it
Almost certainly. We don’t really consider rotational energy - the flywheel effect of a spinning mass - in that it is difficult to measure. We can measure a bullets velocity quite easily and have been able to do so for a couple of hundred years. And easy enough to work out the kinetic energy from mass of bullet multiplied by the square of the velocity.
Rotational energy is about the moment of inertia and the square of the rotational velocity. Moment of inertia is in effect the mass abd the distance it is from the centre of rotation.
Take a dog lead and spin it around - you will feel it pulling on your hand. Spin it faster and will pull more. Add a wee pooch to the end and it will pull more. Add a Labrador and your arm will come out of its socket.
That is what is happening inside a spinning bullet, and as it hits and breaks the bits fly outwards from the centre.
In the early days of high velocity centrefire rifles the quickly found that the traditional lead bullet didn’t work very well. They caused a lot of lead fouling and in many cases didn’t reach the target. This was surmised to be the lead bullet basically spinning itself apart (no high speed photography in the late 1800s early 1900s).
The whole reason for using a copper / steel jacket was to keep the bullet together in flight, and then keeping it together as it goes into the target and this getting penetration. Hence the reason for jacketed bullets.
If you read old hunting / rifle articles from either side of the War when cartridges such as the 22 Swift and 270 Winchester came into being with velocities well over 3,000 fps one of the early complaints was perceived bullet failure with bullets blowing on way to target. This is one of the reasons why these older high Velocity cartridges use slow twist rates - 1 in 14” etc. They have more enough velocity to impart fast enough spin to stabilise a short bullet, but then propel that bullet very fast.
But such bullets fragment and explode on target - doesn’t really matter on a varmint but not so good on a game animal.
They then started using such bonding the core to jacket, or using jackets with bridges across the middle such as the Partition, H Mantle etc. These really came about for high velocity magnum big game cartridges to provide a bullet that would survive the initial impact on a deer, elk, buffalo etc.
Solid bullets have been around since the beginning of the nitro powder era, but it was the likes of Barnes that really brought them to every day hunting. By making a bullet out of solid copper or copper alloy, you remove all the issues of lead not holding together. Careful design of the tip and the annealing of the copper allows good expansion on impact.
Faster twists have been with since the birth of the 7x57, 6.5 Mannlicher and 303’s. The first bullets were like long pencils and required a 1in 8” twist to stabilise. They had superb penetration performance, and indeed pretty good long range terminal performance. But velocities were in the 2,300 to 2,400 fps range, and trajectories were not particularly flat ( but much much flatter than previous black powder cartridges).
Military developments went towards higher velocities with slower twist rates of 1 in 10” in 30-06, 303 which were shooting 150 ish grain pointed spitzer type full metal jacket bullets north of 2700 fps.
This culminated with adoption of 5.56 NATO with a 1 in 12” twist firing a little 55gn FMJ at 3300 fps or so.
This worked brilliant on soft targets such as human flesh, in that the FMJ was on the verge of stability and would tumble on impact causing big wounds. But that little bullet ran out of steam at 300 yards, and wouldn’t penetrate very well.
So they started developing bigger longer bullets and faster twist rates barrels to stabilise them. Modern Nato 5.56mm is using a 63gn bullet with a twist rate of 1 in 7” but muzzle velocities are back down at the 2700 fps or less in shorter barrels.
Coming back to rotational energy I posted a video by Ron Spomer a few months back. An American company has developed a large bore subsonic rifle that to all intents and purposes is silent. It doesn’t produce a lot of kinetic energy - well below the 1,000 ft lbs sorts of levels that are typically thought to be minimum. But it uses a 1 in 3” twist with a very fast spinning copper bullet. This is designed into a spinning blade on impact, that cuts its way through the animal mincing everything in front of it. Reports are that Cape Buffalo have been killed very quickly with it.
