I'm reading a novel in which the author works several historical incidents of shootouts/raids, etc. by the federal government into the story line. The incidents are recanted in great detail, and he was pretty darn accurate on the only one I know any details of (the FBI Miami shootout). He states that during the Waco raid the defenders on the ground level were shooting AR-15s up through the floor at FBI agents on the second story. He says that because the rifles had 1:7 twists and they were shooting standard 55gr ammo the bullets would fragment quickly and did not penetrate the floor as well as they would have had they been shooting a lower twist rate (or of course, heavier bullets). I'm curious if that is true historically (were they really shooting 55gr rounds through 1:7 barrels?) but what I really want to know now is does this theory have any validity? Has anyone done gelatiin testing on lightweight rounds (55gr or under) at 1:7 and do they fragment sooner upon entry than the same rounds at 1:9, for example? I'm guessing that this would have to be true at least somewhat. If you have a lightweight round spinning just under the point at which it will fly apart in air and it contacts a denser medium, it seems to me that it would fragment pretty quickly, although I admit I'm just speculating. Anyone know of any data to back this up?