It's only 1d6 per weapon, so 2d6 for the dual mount. I'd have to see your math to tell you where it went wrong. I've been through most of the Tech Manual table, and I've only found a handful of weapons I can't explain.
Looking at TW page 216 it says burst weapons use the table on page 217. Pulse lasers are burst weapons and would do 2d6 damage against infantry. There's two weapons in a dual mount so that'd be 2d6, each.
Okay found it. Missed the "To a max of 1" part for the reload factor. With that I get 3.25 damage for the Support Pulse Laser. TM lists the Support Laser as doing .81 damage. So I'm not sure what I'm doing wrong.
Here's my math for the Support Pulse Laser.
Infantry Damage Conversion Formula*:
Total Warfare Damage = [(5 x 32.5) ÷ 50] x 1
Penetration Factor = 5
Damage Factor = 5 x (3.5 + (15 ÷ 5))
Reload Factor (Support Weapon) = (13 ÷ 3), to max of 1
(Military Power Pack has 200 power Points and the Support Pulse Laser uses 7 points per shot. A burst is 15 shots)
Weight is certainly one of the differentiators. Mostly, I was trying to avoid different weapons ending up completely identical at the TW scale.
Unfortunately, I think that's what is going to happen since TW scale are scaled up versions.
I think one way to avoid them being completely identical is to include ammo even for energy weapons. That's how it is legally anyway. Plus it makes them different. Standard Laser and Chemical Lasers have the same stats except the latter use ammo. Same principle with infantry weapons. I'm of mixed feelings about heat. Currently they don't need a heat sink in small vehicles. If you did include heat in larger vehicles/mechs you could make the heat sinks dedicated and part of the same system, like an ammo bin. That would further make them different from regular energy weapons.
Outside ammo/cargo bins in Superheavy mechs the only multiple mountings I know of are XTRO:1945 weapons and Compact Heat Sinks. I want to say take the weight of a weapon and all the ammo you want to shoot and increase it 50%.Then round it off. But part of me doesn't wan't to go over .25 tons otherwise, why not multiple mount everything?