I can use a lookup table to replace the muls (just requires en extra entry into the sprites data structure).
I have replaced all the software sprite code's movem.l's with move.l's but there is no change.
What I have noticed though is the border flickers on and off whenever you press fire when there's a lot of screen activity.
I tried adding the blitter save/switch off/restore blitter code into the keyvector routine, but with no luck.
It's starting to get a bit annoying again now coz all I heed is to get this one last interrupt absolutly stable and I can get back to working on the main game code again.