Bolt weapon displays

I'm trying to add a new Bolt type display. It would appear that Bolt 1, Bolt 4 etc etc are contained in the Pulse_xx.bmp files. However, adding a further file (Pulse_05.bmp) isn't giving me the expected results. Bumping the effect number up to Bolt 17 displays something I can't actually find in any of the bitmaps in the Pictures/Effects directory. I know the bitmap I created works because if I copy it over the top of Pulse_01.bmp and set the effect to Bolt 1 I get my customised bolt in all its ugly glory, I just can't get it to work as an expansion to the existing bolt effects. Are the bolts limited to some hard-coded number or have I done something really thick?

The only thing I changed in the components.txt is the number - it was originally Bolt 3 (which works as expected), I changed it to Bolt 17 (which doesn't). Presumably 17 is the correct number - four existing bitmaps, each with four bolt effects, so the last effect included in vanilla would be Bolt 16.

I've had no trouble adding extra beam effects using the same logic.