Doing the “I’m a murderer” joke is a gross take.

Bouyancy is based on how much water is displaced, not amount of air inside the container. 66x12x13=10,296 cubic inches. Fresh water density is about 0.0361 lb/in^3 so that case has to displace at least 372 lb to sink.

Metric would be better for this but we’re talking about a stinger missile here.