Those sounds aren't necesarily from "gunshots" or even ammunition going off -- though they could be. There are many other things that can and do explode in the immediate aftermath of an accident, including oxygen canisters and/or other small pressurised containers.
Good point
Likely tie-in is a gun firing into a canister to make sure it doesn't go off when being handled. Somewhere I have a picture of one of these canisters with a convenient hole in it. They stick out among all the debris because they typically keep their shape