Let's talk bare-bones BOK

[Gutshot John]

As for how quickly a Tension Pneumo kills it really depends.

By definition you have a tension pneumo before you show signs, how quickly it progresses from there depends on the injury. In my experience once the signs are obvious you're behind the curve.

My sense is that you're talking about an open pneumo thorax caused by penetrating trauma rather than a closed pneumo caused by a car accident/paper bag effect or coughing. You can sometimes decompress an open pneumo without a needle by releasing the air then sealing the system with a flapper valve of sorts. You need a needle for a closed pneumo.

A lot of variables there to apply to a barebones kit. Since you're talking about GSW's I'd think a needle kit is less applicable for bare bones.