“Since a regulation-size football weighs 14 ounces, it was considered feasible to make a shaped charge grenade within this weight limitation. In addition, most US troops are familiar with throwing footballs,” according to the Army’s test report for the weapon.
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Footballs fly through the air because there is an even distribution of weight surrounding the hollow inside of the ball. But 14 ounces of explosives tended to make the trajectory of the Nerf grenade “unpredictable,” according to the test report.
Well, this football thing is terrible for a lot of reasons, but the fragmentation radius of a shaped charge munition that is not designed to make secondary frag is actually very low. (Many munitions will intentionally tack some frag on because usually there’s no reason not to, but it’s easy to design a munition excluding extra frag) At that point the blast radius becomes the main factor, which again is relatively low.
Throwing this thing at a tank or armored vehicle is unlikely to make it instantly catastrophically explode. Even the later MPIM munitions, which were almost certainly better explosively designed were only really expected to score mobility kills consistently.
The bigger question is: Do you feel comfortable getting within throwing distance of a vehicle with at least one machinegun on it to toss this thing that will probably just make the crew angry at you?
Too be fair, troops likely had the misfortune of being that close once. At which point having a possible tool for survival is better than none.