I too like to test ammunition against hard objects. I have a piece of rail road track about a foot long, and also a backing plate that the rail sits on, on the tie.
One thing I have found is that speed kills. The faster bullets always penetrate deeper. A .458 Win. will knock it about 20 feet and penetrate about half way. A 7mm Wby will punch a hole all the way through. A .270 Win. makes a dimple. A .44 Mag. does not even make a dimple. A .30-06 will make a crater, but not penetrate all the way. A .300 Win. and and .300 Wby. will make a deeper crater, but not go all the way through.
I have a .300 RUM but have never tried it.
The 7 MM is the only once that gave complete penetration.
I have never tried any fast .22s or .24s or .25s, but I would guess that the faster the bullet, the deeper the crater.
Odd, but the 7mm did not actually penetrate. It knocked a plug out of the steel, about 1/2 inch in dia. It also had the rifling marks inside the hole it left, and also on the plug it knocked out. I found the plug about a foot beyond the steel.
My opinion is that body armour would not be effective with a rifle bullet traveling 3000 FPS or more. Perhaps not even that fast.
What if the attacker is standing behind a large tree and shooting at you? I have found that .30-06 FMJ military will penetrate a pretty large tree.
Sorry - speed in and of itself does not kill. The only thing that kills is cessation of oxygen flow to the brain via CNS shutdown through whatever means. With bullets that is accomplished by tissue damage rendering said systems non-functioning.
