I gave my physics students this question and had them calculate it, but I either don't believe the answer or I don't believe the claims made about this guy.
Col. John Stapp was a pioneer in human/g-force research. In one experiment he went from 0-632mph in less than 4 seconds, then at the end of the run, slowed to 0mph in less than 3 seconds. (You can see it in this video: ) Reportedly, he survived 40 g's of force, but our calculations show only 7 and 9.7 g's. Either we're wrong, or the claim is wrong/misunderstood.

Re: Turning Acceleration into g's -- Is 40 g's a lie?

Your calc is correct. The 40 g's is likely a misunderstanding of the concept of a 'g' force.

Note that if Col. Strapp weighs about 128 pounds (4 slugs worth of mass), then the force acting on him during his deceleration is (4)(309) = 1200 pounds or so, so mistakenly someone may have divided the force by 32 to come up with the '40' , which is the wrong approach, but I'm just guessing, I don't know what they did.....