I've been reading one of John Farnam's books where he states that most modern military style rifles are drop safe, whereas the safety mechanism does more than just block the trigger movement.

I didn't realize this was the case, I was under the impression that almost all modern long guns were NOT drop safe.

I realize free-floating firing pins are one potential concern in certain designs (AR, AK, SKS, etc.), but excluding this, which of the following are drop safe?

AR-15
SKS
AK47
M1

I'm pretty familiar with the workings of the AR and M1 but I haven't delved into the trigger groups, so I'm not sure if they incorporate a hammer block to prevent the hammer from releasing and hitting the firing pin if it were jarred from the sear.