Try a strong, well made tire valve tool from your local auto parts store.
Don't get the buck 380 alloy rubbish, spring for something durable made from steel.
Failing that you can make one with a suitable sized spare hex key & a Dremel to cut the slot.
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”