You can kill 30-40 people in 30 seconds??? You sound like the gun grabbers.
I personally won't, and couldn't in fact, kill anyone unless it's in self defense as a last resort and I am in imminent fear of my life ( and possibly not even then), so It's hard to visualize a situation where I would kill 30-40 people under any circumstance.
However, an AK-47 with a 40 round capacity magazine is easily capable of 40 aimed shots in about 30 seconds. If the shooter is able to aim the rifle accurately and the targets are at close range, say between 0- 75yards, then yes - it is very possible to shoot 30-40 people in that time frame.
People shot at close range with an AK-47 can die from those wounds if they are serious enough and there is no medical care available in a sufficiently timely fashion.
These guns are not toys, they are serious weapons that arms manufactures have spent many years and many millions of development dollars to develop into the most effective weapons possible.
The fact of the matter is that well trained, serious gun owners are responsible owners and operators who respect the capabilities of these weapons and handle them accordingly in a safe, responsible fashion. These owners are also the least likely people to commit a murder or accidental killing.
In Texas, the homicide rate in general is something like 7 killings per 100,000 people.
For serious gun owners with a concealed weapons permit, the rate is 0.6 killings per 100,000 people, more than 10 times lower than the general public, even tough they are much more likely to be armed.