What amazes me is the theoretical rotation rate. If I've done the math correctly, that 38/357 mentioned above with a 1 in 18.75 twist spins at over 30,000 rpm at a muzzle velocity of 800 fps. Worse, a 223 with a muzzle velocity of 3000 fps from a 1 in 9 twist barrel spins at 240,000 rpm.Always amazed me that bullets are at all stable in a handgun, especially a snub, with the bullet only making a small fraction of a turn.
200,000 RPM for a high power center fire rifle is typical.What amazes me is the theoretical rotation rate. If I've done the math correctly, that 38/357 mentioned above with a 1 in 18.75 twist spins at over 30,000 rpm at a muzzle velocity of 800 fps. Worse, a 223 with a muzzle velocity of 3000 fps from a 1 in 9 twist barrel spins at 240,000 rpm.
Somehow I can accept the muzzle velocities, but the spin rate just seems insane lol.
Thanks, that's pretty cool and I never thought about it that way. Just like I wanted to express rotation rate in rpm rather than rps because that's a real-world measure I think I "know".By the time the [above 38] bullet has traveled 25 yards, it only makes about (.19x30,720=5837/60=97.3) 97 rotations from the muzzle to the target. This number is a little easier to digest.
Yes, this can be true but it depends on the actual ammo. Most all 22 LRs have a 1:16 twist rate so when fired from a rifle, a normal high velocity 40 gr bullet will achieve a velocity of about 1250 fps. This spins the bullet at 56,250 rpm. In a 1:9 twist barrel, the same bullet will spin at 100,000 rpm, which close to the threshold where soft lead bullets can fly apart. Chances are ... a 40 gr bullet would still hold together but any lighter bullet (typical MV of 1280 fps for a 36 gr CCI HP) will likely fly apart. If you shoot a 32 gr CCI Stinger at 1650 fps, the 1:9 twist rate will spin the bullet at a whopping 132,000 rpm ... guaranteed to vaporize when it leaves the muzzle.22LR conversions in a high-twist AR15 can fly apart before they reach the target.
I've always thought that shortening a barrel would impact bullet spin; but apparently it generally doesn't ???dhom, Rifling twist rates are set by the manufacturer for the standard factory load. For a 45 Colt it would be a 255gr bullet @ 860 fps. A combination of twist rate and velocity will determine the bullet's spin rate, which in turn will determine bullet stability down range. The faster a bullet is driven, the lower the twist rate needs to be to maintain down range stability. Likewise, the heavier the bullet, the higher the twist rate must be.
Just because a cartridge is capable of being loaded with a heavier bullet, it doesn't mean the bullet will stay stabilized down range. That said, handgun twist rates aren't near as "fussy" as rifles for two reasons. First, with rifles you expect the bullet to remain stable for 300 yards or more, however with a handgun, the typical shooting distance is much shorter ... more like 25~50 yards .... maybe 100 yards absolute maximum. Second, handgun bullets (especially 45 cal) are much larger in diameter than typical rifle bullets so they have way more gyro effect than a skinny little rifle bullet and will retain spin much better. As such, they will maintain stability with a much slower twist rate. A good example is a 38 Special and a 357 Mag. Both use the same diameter bullets and the same bullet weights yet the 357 Mag will develop much higher velocities. Nearly all 38/357 revolvers have a twist rate of 1:18.75, which will maintain bullet stability for nearly all .357 diameter bullets to at least 50 yards.
What MZ5 said. Let's assume a 6" barrel and a 2" barrel with the same twist rates were loaded with different ammo that produced identical velocities from both barrels. The bullet spin rate would be the same from both barrels, even though the shorter barrel would have less than 1/8 of a twist.I've always thought that shortening a barrel would impact bullet spin; but apparently it generally doesn't ???
I have a 1-in-9 Rock River and was looking into the simple conversion. Decided several things for myself, though YMMV:Wow - guys (and gals)!
. . . I was considering getting a .22 conversion (or .22 upper) for my AR, a 20" (1 in 9). After reading this, it seems like that might be a waste of money.
Or at least I'd have to get the heaviest .22lr ammo that I can find.