The thing is that if you implement RoF in standard 10 second turns, the simplest thing to do would be simply have them make multiple attacks as if you had more than one of those weapons. In game play, what's the difference between a single Medium Laser that shoots twice during one turn, and TWO Medium Lasers that each only fire ONCE during one turn? AFAICT, there'd be no difference at all until the double shooting Medium laser takes a crit.
If a weapon can fire more per turn, just resolve each attack separately as if they were different weapons; it need not be any more complicated than that. And it's not like there's any shortage of mechs with lots of little weapons anyway.
Okay, sure, there'd be a difference in mech construction, but construction is not game play.
We've handled Ultra and Rotary AC in exactly this way, and it works great. Incidentally, just having every shot past the first jam on a to-hit roll of '2' is almost identical, statistically, to the RAW jam probabilities.
If I were going to fix autocannon, I'd use the following rules:
-"Light" autocannon are renamed "Snub Autocannon", since that's what they really are.
-AC/2 are renamed "Light Autocannon"; AC/5 are renamed "Medium Autocannon" (or just "Autocannon"); AC/10 are renamed "Heavy Autocannon"; AC/20 are renamed "Assault Autocannon". In-character names referring to game-mechanic numbers make my teeth itch.
- All Autocannon use caseless ammo (double listed ammunition per ton), and can be unjammed following Rotary AC rules..
- HV Autocannon have a maximum RoF of 1.
- Standard, Snub and LB-X Autocannon have a maximum RoF of 2.
- Ultra Autocannon have a maximum RoF of 3.
- Rotary Autocannon have a maximum RoF of 6.
The first shot per turn is made as normal; subsequent shots jam on a to-hit roll of '2'.