Problem is that terminal ballistics just isn't an exact science. Ballistics is. Gravity, mass, velocity yadda yadda. But impact? You can put loads of work into how a bullet is supposed to behave, but there are so many variables when you take the shot that you can really only express the outcome in terms of averages. I have shot (and killed) a lot of things and could I describe a typical impact? Not really. I have shot stags with a 7mm that had almost no signs of impact, entry or exit. I mean plop, dropped on the spot at 200m still with a mouthful of grass. But inside was soup. I've shot other animals that ran on, but when recovered where almost cut in two. It doesn't matter how good a shot you are, you cannot account for what happens when the bullet strikes. So really to a degree what the GC or more accurately as Moggy say the Hague convention requires is frankly pretty random. It's not the strike that counts it's the intent. Dum Dum though really is not a phrase recognised by people who shoot. It was the name of an ammunition manufacturing facility near Calcutta where the .303 British was produced. It sort of passed into folk law as it were. You have hollow point, spire point, round nosed, full metal jacket, boat tail, wad cutter, semi jacketed and many more. No one anywhere in any shape or configuration sells a Dum Dum. It was a case of "Those new bullets from Dum Dum" Rather then "These new Dum Dum bullets" I'm afraid. I have records but couldn't possibly count the number of rounds I have loaded but it runs in the tens of thousands; I used to shoot between 200 and 300 hundred rounds per week at one point. You can produce a consistent point of impact but after that the bullet really does what it wants. Here's a group shot at 100 meters. approx a 20p piece. There are 15 rounds in there. Where they went after that is anyone's guess.
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