You're going to get some posts to this question that say it is possible. Somebody is going to say that they dropped a shell/box of shells and one went off. Maybe they tossed them in the car and ,,, BANG,,, "it just went off". Somebody will point out that a bullet wouldn't shoot out, it would be more like a firecracker if the shell did in fact "go off" without being in a gun.
Yeah, all that is possible, but the odds of it happening, now that's another story. However, the odds are pretty good that the clip will fall out of your pocket and you will loose it. I wouldn't have a reasonable concern about a shell going off in my pocket.
There is in life perhaps one fleeting moment when the courage, dedication and resolve of one man gambling against all odds will alter the destiny of nations.