This month's Shooting Tiimes (Dated April 2012, newly arrived by mail and probably on the newsstands soon) has a very good article about twist rates and bullet weights in .223 rifles. ^:)^ (I know, it's probably bullet length that's important rather than weight, but assuming lead cores and copper jackets, the two go together.)
It doesn't discuss .223 vs. 5.56 chambers, but I came away with three generalities:
1. Rifles are individuals, and many factors influence accuracy.
2. "Too fast" a twist (like a 1:7 or 1:8 barrel for 55-grain and under bullets) might not give the absolutely best accuracy, but the loss of accuracy is relatively small and not a factor for Appleseed-style shooting.
3. The only thing that absolutely won't work well is heavy bullets (70-grain +) in slow-twist barrel, like a 1:12 or 1:14 rifling. A test group, from a 1:12 rifle, which had shot inside 1 MOA with loads it liked, gave a 26" group (at 100 yards) with 90-grain match bullets! Many of the holes in the target showed bullets passing through sideways.
So you've gotta go shoot, in order to know!
Just like the duffers in hunting camp, who can't dependably keep all their shots on a volleyball at 75 yards, debate long into the night over which cartridges/rifles/loads are best for antelope or sheep beyond 500 yards, the gun store commandos and internet experts can give you all the reasons why you need the exactly the optimum twist for the bullet you're shooting. You don't have to believe it. :DH:
Didn't read the article, but it is possible for a to fast twist barrel to spin apart a soft or especially a hollow point bullet. If your twist is 1 in 8 inches the bullet will spin 1 and 1/2 revolutions for each foot of forward travel.
Muzzle veloicity 3000 FPS bullet rotation 4500 RPS, yes that's 4500 revolutions per second.
The few times I have witnessed this, a string of shots would have some fliers and some never hit the target.
If anyone was watching, they might see a gray puff between the fireing line and target line when a bullet came apart. Sometimes the bullet will streak in flight.
I doubt it would ever happen with full metal jackets.
It's a rare thing in .223, just about unheard of in a .308, much more likely in a fast twist .22-250 with velocities above 3500.
I've seen a 55gr .224 bullet come apart in flight after being fired from a 1in7 twist barrel at 400 yards. At closer distances there's probably not enough flight time.
With 1 in 7" twist, a bullet leaving the muzzle at 3000 feet per second, would rotate at at 5214 revolutions per second.
There is not a whole lot of resistance to the bullet spin until the bullet strikes something solid, so even though the forward motion slows, it is still spinning like crazy way down range.
edited for math error
math in public you know.
Remington factory loaded .22-250 with 55 grain power loct hollow point could not stand up to 1 in 8 twist today. You could see them come apart from 20 to 50 yards down range.