I get the funny feeling I might get flamed over some of this but never mind.
Seeing as in both DH and IH there are rather less variants of heavy weapon than there is any other weapon type I decided to have a go at filling some gaps.
These weapons are all manufactured by G.A.C. Mobile Manufactories. ( its a factory ship supported by a small fleet of mechanicus vessels, I dont know if there is any prior fluff about factory ships) They speicialise in heavy weaponry/ vehicles and the following rules are designed to represent the large two man weapons the guard minis get in 40k.
(I'll think of cooler names later)
Crew served tripod mounted Heavy Bolter:
Dam: 2d10+10 X
Rld: 3 full
Crew served tripod mounted Autocannon:
Dam: 4d10+10 I
Rld: 3 full
Crew served tripod mounted Lascannon:
Dam: 6d10+10 E
Rld: 4 full
*Crew Served: These large cumbersome weapons are not designed with mobility in mind and as such sacrifice it for higher firepower and greater capacity for sustained fire. Crew served weapons require two people to operate them at full capacity and cannot be fired whithout bracing even with the bulging biceps talent (my justification for this is that they are bloody huge). While not reloading the second crew member can fire whatever weapon they may have (no larger than basic) but cannot move away from the heavy weapon. If operated by one person an extra round is added to the reload and the weapon gains the unreliable trait. It takes a full round to pack up the heavy weapon so it can be moved and must be carried by both crew members.
Well there you go feel free to pick away at any (hopefully not too many) faults