The Brodie helmet was surprisingly bullet resistant
Mike B recently did a ballistic test on a historic WWII-era Brodie-style British Mark II steel helmet, and it is fairly surprising.
Don’t freak out too much about destroying a collectible, as the helmet is a high-use specimen that had gone to Pakistan and been reimported for sale to reenactors. Plus, the Allies made something like 12 million of these helmets between 1938 and 1944, so they aren’t that rare (you can find them for like $50).
Still, it surprised me how resistant it was to pistol rounds.