If he is using the carracosta set, i would assume there were no stealth rocks on his side of the field, or he was at 100% HP, otherwise the set would not make any sense. So when Amoonguss switches in, carracosta is at +2 attack without leichi berry at full health. so why wouldn't he use shell smash again if another poke is asleep, as amoonguss cannot ohko. Then he would be at +5 attack with 1 hp left (assuming the opponent doesn't use body slam), and stone edge would always kill (of course unless it doesn't hit). Life orb would just ruin hit sturdy, he'd be better running solid rock in that case. Or not even setting up while an amoonguss is on the opponent's team. That just wouldn't make any sense setting up if you know amoonguss can foil your strategy with spore. I mean some common sense applies (yet again, body slam amoonguss..). But what about running the novel idea of lum berry on carracosta? If amoonguss tries to spore, you have lum berry to awaken you and then be at +4 with sturdy still in tact, and then fire off a stone edge which will kill max defensive amoonguss 87.5% of the time? Of course, the fact that this carracosta would be to attempt to counter amoonguss is crazy in and of itself.
Also, the damage formula gives up to 16 different randomly generated amounts of damage a poke can give, so DTC, it is impossible for a poke to have a 1% chance of OHKO, but rather 6.25% would be the lowest.