Sherlock deduces that 'Ammo' should be Amo, the Latin word for I love, suggesting Lady Smallwood, whose code name is Love. Sherlock visits Mycroft and analyzes the situation. Mycroft explains that he previously hired A, G, R, A' but hasn't since the failed mission. Mycroft also states that he has no knowledge of 'Ammo'.
Later, Sherlock calls Mycroft and explains that “Ammo” is really Amo, the Latin word that means “I love”. Lady Smallwood, whose code name is Love, is questioned by Mycroft. Sherlock later puts together the final part of the puzzle when he remembers Mary explaining the best thing about 'subordinates' bringing information but still being under everyone's noses. Meet Vivian Norbury at the London Aquarium.
Vivian reveals that she warned terrorists in the rescue so that the hostages and 'A, G, R, A' could be eliminated. Why did the ambassador mention ammunition to the man? Mary already knew it would be Vivian because she had spoken to Mycroft, but this was really the first time she met the woman face to face rather than as a voice on the phone all those years ago. He didn't mean he didn't expect to see her there, Sherlock told him who the real ammunition was years ago. So I'm sticking with frangible ammunition this week, and if it turns out I'm wrong next week, I don't care.
Once Mycroft arrived and told Mary that the ammunition change was complete, it was a different story. Also, if you're a weapons expert, remember that any answer they choose in the program for the ammo exchange will probably be on the Magic TV Spy Stuff limit. His confession in Tbilisi was genuine: he was not someone who took the blame while the real ammunition remained uncaptured and wandered free. But I did find studies that say no, frangible ammunition will not fully penetrate body armor as long as the right conditions are met.
There is no basis for this, but while watching T6T I began to think that maybe AMMO is another acronym, like AGRA, of an organization like AGRA, but rather to control people. For simplicity, I'll write this assuming they had it in mind as an option for a while, but they didn't know exactly how or when they would make it possible until Sherlock came to them to ask them about ammunition. During his torture, Ajay heard whispers that “Ammunition” and “the English woman” were the reason for the mission's failure. So all Mycroft needed to do was distract or worry Vivian and grab that bag long enough to change Ammo's ammo.
A failed rescue mission for members of the British embassy in Tbilisi, Georgia, under a coup d'état (triggered by the keyword “Ammunition”) resulted in the death of embassy members and Mary's flight. After considering a number of options, my current best option for ammunition exchange is some type of frangible ammunition. Because Vivian started with normal, easy-to-die bullets in her gun, Mary had to be careful until Mycroft confirmed that the ammunition had been changed.
