Fudging Weapon Inaccuracy

'm working on a new combat system where I squish a few pet peeves I have about combat systems.
Something I want to add is, i don't know the name for it, where the faster you fire bullets, the wider the spray, and the more off-target the bullets get.

What I'm trying to figure out, is what's the best way to do this?

Say, I have it set to single shot, and I'm rapping off shots like crazy, i want it to spread wider with each shot until they cool down and give it a little bit to reset.
And if they're in automatic, it needs to slowly spread wider up to the sanity limit.

any ideas?

I tend to simulate inaccuracy with a random modification to the bullet's velocity vector. For that sort of thing, I would probably have an incrementing "inaccuracy" counter which increased with the number of bullets fired, to multiply this modification, by up to a certain limit, zeroed if the trigger was released and not pressed again for a certain time (so the check is actually on each trigger press, probably using llGetTime). I did this with my .45 Shansi for barrel climb, in fact, though these days I'm sure I would script it better.

In fact quite a few of my weapons have some level of built-in inaccuracy now I come to think of it. So dull if every shot just goes to the same point if one stays still.