I don't have vast experience with this, but the way I finally nailed my zig-zagger was to get directly astern at short range, wait till he finished a zig, then at the moment he began his next zag I aimed for his bow with a magnetic pistol set for under the keel (and with TDC set to zero speed so the torpedo simply went in the direction of my crosshairs). It's tough to evade that, because he's already heading in that direction, and if he doesn't change course he's definitely going to get hit, and if he does change his course he won't have enough time to get out of the way and he'll still get hit. That's my theory, and it's worked a total of 1 out of 1 times so far :P Of course, with magnetic pistols there's a better chance of a dud, but I haven't had much problem with duds yet and besides, an impact fuse on a zigzagging target is just as much of a gamble as a magnetic fuse that is almost sure to cross under his keel. Plus, there's no calculating involved, just get on his 6 and blast him John Wayne style
