Tumbiling ammunition? No, The 5.56 ammunition SS109, which is the British design does not tumble. Dosen't need to. You get hit by one, and there is none of the Argh, tie a hankie round it and defeat the baddies. You stay down! As a bullet enters the body the round dumps it's kinitic energy as heat. The result , as the body is mostly water is to boil the water change it to gas and cause what is known as Cavitation. A large void around the area of impact, but this mostly closes as the round passes .To see the effect of a standard 78 grain .22 rimfire bullet on Ballastic Gelatine , which retains the cavitation is a dam good saftey aid.
A soft round such as pure lead or a semi jacketed round (The most efficent manstopper is reckoned to be a 125 grain semi jacketed .357 S&W Magnum revolver round) Will intial expand but lacks penetration. All military rounds are fully jacketed, for ballistics and penetration. As the round slows and encounters harder material such as bone and gristle then it's course will be deflected causing a jagged wound track.
The tumbiling bullet is another Great War myth. The Germans issued a SKM 7.92 round, initally for use aginst aircraft later aginst tanks. This was the standard 7.92 round with the bullet withdrawn and replaced head first so the flat end hit the target. the rseult was a semi armour piercing bullet with the outer jacket folding back from the lead core. It was effective against the first tank armour. Prisioners found with these rounds were often given short shrift. If a bullet tumbles on impact it has to be inherently unstable, therefore when fired, where is it going to go? No use firing at a target if your not going to hit it.
The American experience with 5.56 M109 amunition in Vietnam was the stuff was bl**dy useless! The problem is that being a light round it is easily deflected by hitting leaves or branches and lacked penetrtation. There was also the dosen't need cleaning myth of the M16, till the propellant formula was changed, without anyone being told. Why change? The intial charge was found to make the bullet unstable in flight, so you didn't know where it was going. The 7.92 Kalasnikove round was able to penetrate undergrowth
To give you an idea let me quote an old story, Richard Couer De Lion is said to have entered Saladin's camp. Saladin drew his light sharp sword, threw a silk cloth into the air and sliced it in two before it hit the ground. Richard drew his broadsword and split an anvil.
One very effectve is the so called Air Marshall round. This looks like a small wine gum, with distilled water in the middle (Distilled to prevent infection, go figure) This is deliberatley designed to have little or no penetration and is the eqivalent of Richard's broadsword, a supersonic sledgehammer.
The best book I can think of about the Burma campaign is Geroge Mc Donald Frazer's Quartered Safe Out Here. And yes he does go into quite a lot of detail about the morality of war out there. To wit, I survived, that is what matters.