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.
